THE AGE OF THOUGHT
By: Richard J.Kosciejew
Glacier are an enduring accumulation of ice, snow, water, rock, and sediment that move under the influence of gravity, glaciers form where the temperature is low enough to allow freely hanging snow to accumulate and slowly transform into ice. This accumulation is most common in the polar regions, but can also occur at high altitudes on mountains even near the equator. Glaciers are complex systems that grow and shrink in response to the climate. At the present, glacier ice covers about 15 million sq. km (5.8 million sq. mi), or 10 percent, of Earth’s land area.
Glaciers occur on all continents except Australia. Antarctica and the North American island of Greenland have the largest continuous ice masses. Ice covers their land areas almost completely. About 80 percent of the fresh water on Earth is frozen in ice sheets and glaciers. If all of this ice melted, sea level would rise by 60 m’s (200 ft). Much of the world’s population resides in coastal areas that would be underwater. Glaciers are an intriguing part of Earth’s natural environment and their majestic beauty in wild and inaccessible mountain settings are unparalleled.
Glaciers occur in many different forms and locations, from the big ice sheet that covers the entire continent of Antarctica to the small valley glaciers that are present in many parts of the world. They are generally divided into several categories depending on their size and location. Glaciers categorized by size include ice fields, ice caps, and ice sheets. Glaciers categorized by location include alpine, valley, and Piedmont glaciers.
Ice sheets are the largest ice masses found on Earth, covering huge land areas. The ice sheet in Antarctica covers 13 million sq. km. (five million sq. mi). It is more than 4 km. (14,000 ft.) thick and its weight has depressed the continent below sea level in many places. If this weight were removed, the continent would slowly rise and readjust itself, as Europe still does after the melting of the ice sheet that covered that continent during the last ice age. Antarctica’s ice sheet and the similar but a smaller ice sheet that covers Greenland both flow slowly downslope. Embedded in these flows are fast outlet glaciers that break up when they reach the ocean, forming large icebergs. The largest outlet glacier, the Lambert Glacier in Antarctica, is 40 km. (25 mi.) wide and 400 km. (250 mi.) long, draining one million sq. km. (about 400,000 sq. mi.) of eastern Antarctica. The iceberg that sank the Titanic originated with an outlet glacier in Greenland.
Ice caps are smaller than ice sheets. They form when snow and ice fill a basin or cover a plateau to a considerable depth. There are many ice caps in the Canadian Arctic, Alaska, and other heavily glaciated areas. When these ice caps become thick enough, tongues of ice overflow the basins and discharge ice through valley glaciers.
Ice fields develop where large interconnecting valley glaciers are separated by mountain peaks and ridges that project through the ice. These exposed rock features in the surrounding ice are called nunataks, an Inuit word. Ice fields are common in Alaska, where they occupy up to 4,000 sq. km (1,500 sq. mi) each.
Valley glaciers flow from ice caps or originate in high mountain basins where snow accumulates. They can erode the landscape very effectively, producing U-shaped valleys in their descent. These U-shaped valleys are a common feature in many landscapes that were once glaciated and that remains after the glacier is gone. Some of these valley glaciers can be up to 1,000 m’s (3,000 ft) thick and 160 km (100 mi) long, but most extend only a few miles.
Alpine glaciers are also sometimes called mountain or cirque glaciers. They are found high up in the mountains and lean toward identical smaller valley glaciers. A cirque is a rounded bowl-shaped depression in which snow accumulates easily. Ice flows out over a lip in the cirque and often cascades down into valley glaciers through icefalls or stops halfway in steep hanging glaciers.
Piedmont glaciers are broad lobe-shaped ice masses that form when one or more valley glaciers flow from a confined valley and spread over low-lying slopes below the mountains. There are two good examples of Piedmont glaciers in Alaska, the Malaspina and Bering glaciers. Each covers more than 2,000 sq. km (800 sq. mi). The Malaspina glacier is larger than the state of Rhode Island.
Rock glaciers are an entirely different type of glacier in which rock, not ice, is the main material. They resemble regular glaciers in shape but no ice is visible. Ice fills the space between the rocks, however, and allows the glacier to move downslope, although only very slowly.
Glaciers wax and wane not only with long-term climate change but also on a seasonal basis. Snow falls in winter, accumulates, and slowly turns to ice when it is compressed by additional snow loads. In summer the upper snow layers thaw and meltwater runs off; this loss is called ablation. The glacier’s mass balance or budget then turns from positive to negative as it loses mass. The balance is neutral or in equilibrium from year to year if the glacier does not experience any mass loss or gain. A complex series of processes determines the glacier’s health.
Snow falls as small crystals on a glacier and accumulates if temperatures are below freezing. These snow crystals are found in an infinite variety of hexagonal shapes formed when the hydrogen and oxygen atoms of water arrange themselves in a six-sided symmetry upon freezing. Under the weight of successive snowfalls the snow is compressed. Snow crystals settle and change shape and size as the weight packs them closer and closer together. Air passages between crystals disappear and only small air bubbles remain. The snow has now turned into ice with a density of 820 kg per cu m (1,380 lb per cu yd). As snow piles up, the ice crystals that at the surface were smaller than a millimetre (0.04 in) merges, growing to three to 5 cm in size (1.2 to two in) or even larger.
Most glaciers have two parts, an accumulation surface area and the emittance or wastage area. In the accumulation area snowfall exceeds melting in each year. In the ablation area melting exceeds snowfall. The boundary between the two areas is called the annual snowline or sometimes the firn limit. In winter most glaciers are entirely snow-covered. In spring the snow cover begins to melt in the lower reaches, exposing the ice surface. As temperatures increase, the melting moves up the glacier. The snowline is the highest position the melting reaches during the year. Firn is old granular snow. The firn limit may not exactly coincide with the annual snowline since in some years rapid melting leaves behind firn patches below the snowline.
Some glaciers exhibit features called ice streams and icefalls. Ice streams are valley glaciers that form tributaries to a common compound glacier that fills a valley. The tributary glaciers do not intermix but maintain their individual streams of ice, despite compression and extension as they move along side by side. The streams can easily be recognized as individual ice streams by the deposits of boulders, gravel, sand, and mud that separate them. Icefalls occur where a glacier flows over very steep terrain that accelerates the flow. The ice is stretched and fractures into large blocks and a maze of ice pinnacles called séracs and cracks called crevasses. Icefalls are spectacular features that can extend over the entire width of the glacier and over a height of up to a kilometre (3,300 ft). Ogives, regular undulations in height on the surface of the ice, form below icefalls. Scientists believe different rates of flow in summer and winter create ogives, and that ogives therefore present some indication of annual ice movement.
Although ice is normally brittle, it can flow under pressure. The speed at which glaciers move depends on several factors, including their temperature, the meltwater at the bottom of the ice, the steepness of the slope, and the nature of the rock surface over which they move. The big ice sheets move by internal deformation as ice building up in the middle forces the edges to expand. Valley glaciers move by sliding over their rock beds. Friction with the ground produces heat that in turn melts ice and helps to lubricate the sliding. The experimental assessments of glacier activities suggest that they, in effect, displace their fastest at the midpoint of the glacier under which the ice is practically impenetrable. Valley glaciers typically sustain velocities of 30 to 60 cm (one to 2 ft) per day or 100 to 200 m’s (300 to 700 ft) per year, but some can reach speeds of three to six m’s (10 to 20 ft) per day. On the large outlet glaciers in Greenland velocities of more than 30 m (100 ft) per day have been measured. Short-term advances in so-called galloping or surging glaciers can reach 80 m’s (250 ft) per day.
As glaciers move downslope they twist and stretch. This may cause the ice to crack, forming crevasses that can be more than 30 to 40 m’s (100 to 130 ft) deep and up to tens of metres wide. Freshly formed crevasses have clean, straight sides. Over time, crevasses deform and may be covered over by snow bridges when drifting and blowing snow accumulates on their lips. Vehicles or people travailing on the snow’s surface can fall through the snow into a crevasse.
Scientists measure the thickness and movement of glaciers using a variety of methods, including conventional surveying techniques to record the movement of marker stakes drilled into the ice. The latest techniques use lasers on aircraft to figure out height changes, and satellite interferometry for movement. Ice thickness was previously measured through seismic methods in which the time it takes for a sound wave from an explosion at the surface to travel to bedrock and back was recorded. More recently radio echo sounding - bouncing radio waves from aircraft from both the surface and bedrock of the glaciers - has replaced seismic methods. Once they gather information on how the thickness and rate of movement of a glacier vary over time, scientists can calculate the glacier’s mass balance. The vast and expansive enormities of the ice sheets entrenched of Antarctica and Greenland, are, however, made by difficulties to distinguish the massive balances whose area is localized by this is the consequential aptitude of attributive climacteric orientations.
Glaciers are very effective agents in shaping Earth’s surface. Wherever glaciers flow, the topography is changed. Glaciers erode material as they move, and deposit that material farther along their paths, forming several easily recognizable features that are characteristic of areas that were once glaciated.
Glaciers typically gouge out U-shaped valleys. Glaciers sometimes create these valleys near the coast. When the ice retreats from these coastal valleys, it leaves behind fjords, narrow inlets flanked by steep mountains on either side.
Horns, arêtes, and cirques are the most common features of exposed rock seen in recently deglaciated areas. Arêtes (from the French word for fish bones) form when glaciers erode ridges separating two glaciers and produce a narrow, sharp and jagged ridge line. When four glaciers eroded a mountain on all sides a pyramidal mountain peak remains, called a horn; the best known of these is the Matterhorn in the Swiss Alps. Roches moutonnées, a nomenclature given to the French culture, literally interpreted as “fleecy rocks,” and, seemingly omit the connotation that would strictly imply the feeding or gazing of sheep, and its emergent infraction defines of large rounded bedrock when a glacier recedes. These ‘fleecy rocks’ are characterised of composites that are structurally unstable, yet, by things abounding to the nature of climactical conditions creates some rocks of grinding them down.
As glaciers recede, they leave a sharply defined boundary on the sides of valleys. These boundaries are called trim lines and are marked by sudden changes between the presence and absence of vegetation and of unweathered and weathered rock. Striations (grooves) on flat rock surfaces also appear as glaciers recede. They are produced as glaciers drag and grind rock debris over the surface of underlying bedrock. From these striations the direction of glacier movement can be deduced.
As glaciers move over bedrock they scrape and abrade its surface, producing fine-grained rock flour. Glaciers can also pluck away rocks up to boulder size and transport and deposit them along the margins of the glacier down in the valleys. The glaciers deposit these materials as till, a sediment consisting of mud, sand, gravel, and boulders. Much of this material is deposited in long mounds called moraines. Lateral moraines are formed on each side of a valley glacier where abraded sediment and plucked rocks are deposited. These moraines are often preserved when glaciers melt and can show previous glacier heights. Medial moraines separate tributary glaciers that flow into a compound valley glacier. Terminal or end moraines mark the farthest distance down a valley that a glacier has reached in its advance. Recessional moraines show to where glaciers advanced and remained stationary for some time in the past. Both terminal and recessional moraines can dam meltwater streams, forming glacial lakes. Glaciers also deposit a blanket of tills that forms a ground moraine on the surfaces over which the glacier flowed.
Material eroded by glaciers is also transported by running water and deposited on gentle slopes in front of the glacier. These slopes are called outwash plains. Occasionally large blocks of ice are left behind on the outwash plain by a retreating glacier or are washed out onto the plain by jokulhlaups, outburst floods from ice-dammed glacial lakes caused by the collapse of the ice dam. These blocks of ice slowly melt and form depressions called kettles. Another deposit called kame is formed when running water meets stagnant ice. These deposits form within cracks, holes, and crevasses. Kame terraces form between glaciers and the valley walls that enclose them and can sometimes be mistaken for lateral moraines. Running water under glaciers can erode channels that fill with sediments. When the ice melts, the deposits remain as winding ridges called eskers that can be up to 30 m’s (100 ft) high. Drumlins are clusters of elongated hills of a till, oriented parallel to the direction of ice movement and laid down near the margins of large ice sheets as they retreat.
Glaciers are very sensitive to climate change. Their size, life span, and history of growth and retreat all depends strongly on climate conditions. Since they are so sensitive to climatic changes, they also serve as good indicators of change. A galactic infraction given to lay the hidden accumulation or gainfully lose of its masses. Structural content, it has primarily independence on a differentiating climate where temperatures and on solar radiation. Its humidity plays a more common role than previously thought, in that, the wind speed alone, for instance, can localize largely and at time an enormity of snow, rock, etc. to the freedom of orientation. This sorted exposure toward glacialis importance, has to its importance the inclination for valley glaciers, least to mention, the glacially antarctic winds are presently to blow were man seldom ventures, because of the instances given to previous experimentation.
The manifestation of balance or counterbalance of a glacier’s surface reflects about how frequently and regularly the heat radiancy of omitting energy is received or perhaps lost from a glacier, and whether evaporation or melting can occur. The allotment to energy explains the quantitative indifferences that are termed the microclimate of a glacier.
The large ice sheets can provide information about climate conditions over the past several hundred thousand years. Cores drilled deep down into the ice in Greenland and Antarctica allow the reconstruction of past climates since the analysis of successively deeper layers of ice yields information such as the atmospheric temperature at the time the ice was first deposited as snow. Dust layers from known volcanic eruptions provide reliable age determinations; ice that lies beneath a known dust layer is older, while dust that lies above is younger. Analysis of the ice itself and of the air bubbles trapped in the ice allows deductions about the composition of the atmosphere at the time when the ice was deposited.
Historical climate records generally do not go back more than 2,000 years, but past climates can be reconstructed from many different sources of evidence. Tree rings, for example, can provide information on a climate during the past 1,000 years; ice cores can cover the past 100,000 years; lake sediments furnish evidence stretching back as much as a million years; and marine sediments can yield data covering the past 10 million years. Scientists have used a combination of this evidence to find that ice ages, cold periods when Earth’s temperature is about eight°C (14°F) colder than during the warm, so-called interglacial periods, occur at roughly 100,000-year intervals. They believe that cycles of changes in the distribution of sunlight due to long-term variations in Earth’s orbit and the inclination of its spin axis to the Sun cause ice ages. These cycles are known as Milankovitch cycles, named for the Serbian mathematician who first computed them.
Nonetheless, radiocarbondated sites attest to human presence in Australia/New Guinea between 40,000 and 30,000 years ago (plus the inevitable somewhat t older claims had expanded over the whole continent and adapted to its diverse habitats, from the tropical rain forests and high mountains of New Guinea to the dry interior and wet southeastern corner of Australia.
During the Ice Age, so much of the ocean’s water was locked up in glaciers that worldwide sea levels dropped hundreds of feet below their present stand. As a result t, what is now the shallow sea between Asia and the Indonesian islands of Sumatra, Borneo, Java, and Bali became dry land. (So did other shallow straits, such as the Bering Strait and the English Channel.) The edge of the Southeast Asian mainland then lay 700 miles east of its present location. Nevertheless, central Indonesian islands of Bali and Australia remained surrounded and separated by deep water channels. To reach Australia/New Guinea from the Asian mainland at that time still required crossing a minimum of eight channels, the broadest of which was at lest 50 miles wide. Moist of those channels divided islands visible from each other, but Australia itself was always invisible from even her nearest Indonesian islands, Timor and Tanimbar. Thus, the occupation of Australia/New Guinea is momentous in that it demanded watercrafts and provided by far the earliest evidence of their use in history, not until about 30,000 years later (13,000 years ago) there is now of some proof that existed of a convincingly strong provision of evidence of watercrafts anywhere else in the world, from the Mediterranean.
Initially, archaeologists considered the possibility that the colonization of Australia/New Guinea was achieved accidentally by just a few people swept to sea while fishing on a raft near an Indonesian island. However, believers in the fluke-colonization theory have been surprised by recent discoveries that still other islands, lying to the east of New Guinea, were colonized soon after New Guinea itself, by around 35,000 years ago. Those islands were New Britain and New Ireland, in the Bismarch Archipelago, and Buka, in the Solomon Archipelago. Buka lies out of sight of the closest island to the west and could have been reached only by crossing a water gap of about 100 miles. Thus, early Australia and New Guinea were probably capable of intentionally travelling over water to visible islands, and were using watercrafts sufficiently often that the colonization of even invisible distant islands was repeatedly achieved unintentionally.
Why, despite that had a start, did Europeans end up conquering Australia, than vice versa?
Within that question lay another. During the Pleistocene Ice Ages, when much ocean was what it was sequestered in continental ice sheets and sea level dropped far below its present stand, the shadow Arafura sea now separating Australia from New Guinea was low, dry land with the melting of ice sheets between around 12,000 and 8,000 years ago, sea level rose, that land became flooded, and the former continents of Greater Australia became sundered into hemi-continental of Australia and New Guinea.
The region of Southeast Asia to Australis and New Guinea are to have an authentic present coastline ground, as are the coastlines during Pleistocene times when sea level dropped too below its status - that the edge of the Asian and Greater Australian shelves at that time. New Guinea and Australia were joined in an expanded Greater Australia, while Borneo, Java, Sumatra and Taiwan were part of the Asian mainland.
Earth, least of mention, is in a warmer glacial period and ice covers only about ten percent of the land’s surface, compared with 30 percent during the last ice age. During the last ice age, however, ice covered nearly 30 percent of the land. At its peak about 18,000 years ago ice sheets a kilometre thick covered most of North America and Europe. When the ice melted sea level rose by tens of metres, flooding large areas including the Bering land bridge that had served as a migration corridor for people moving into North America from Asia. During the present warm interglacial period these two large ice sheets have slowly per-century dismissed and now smaller glaciers peak of a worldwide shrinkage, however, these infractional occurrences have uncommonly been due by angularity of momentum to Earth’s axial rotation about the Sun, causing over centuries a general decline for the inhibition to become more unduly influenced.
At the end of the last ice age, about 13,000 years ago, the climate was beginning to warm and glaciers were retreating during a period called the Bolling-Allerod when the climate suddenly plunged back to ice-age conditions. This 1,300-year-long cold period is named the Younger Dryas because the polar wildflower Dryas octopetala had a resurgence in Europe during this period. Temperatures in Greenland dropped nearly seven°C (13°F), back to full ice-age conditions, and glaciers advanced to cover the island. At the end of the Younger Dryas the climate returned to warmer and wetter interglacial conditions.
A continent is distinguished from an island or a peninsula not merely by greater size but also by geological structure and development (see below). The continents, in order of size, are Eurasia (conventionally regarded as the two continents of Europe, individually the second smallest, and Asia), Africa, North America, South America, Antarctica, and Australia.
The continental arena - all regional points of al lands arising above sea level - figures of a reasonable measure that incline to inclinations of roughly 29% of amounting to the earth's enumerate area. Other than two-thirds of the continental terrains stretch out north of the equator. In addition, the continental accumulations of land masses do include the submersed areas that are innvisalizable to the surface constructs or constructions that are structurally seeable horizons vulnerable to the continental shelves. These immersed and unseen partialities belonging to the continental shelve, under which slope gently from the ocean shores of the main land, or its basically least emergent of continents valued gradient descents to depths of about 183 m (600 ft); at roughly this point there begins the more abrupt plunge into the oceanic depression known as the continental slope. If the continental shelves are taken into account, the total continental area increases to 35% of the earth's surface. Islands standing on the continental shelf of a given continent are considered part of that continent. Prominent examples are Great Britain and Ireland in Europe; the Malay Archipelago and Japan in Asia; New Guinea, Tasmania, and New Zealand in Australasia, Greenland in North America.
In geology, continents are to the earth's crustal structure and constituency, rather than land-surface areas. Geophysicists have studied these features by using seismography records of shock waves produced by earthquakes. Their data suggest that the centre of the earth be a hot, dense, partly molten nickel-iron core more than 6000 km (more than 4000 mi) in diameter. Surrounding this core is a mantle of hot, solid rock, 3000 km (1800 mi) thick, part of which is semi-plastic. This is enclosed, in turn, by the earth's outermost shell, the crust, a layers of potentially cool rock ranging in thickness from an average of 5-10 km (3-6 mi) beneath the oceans to 40 km (25 mi), on the average, beneath the continents.
An occurring reservoir of a continuatives supply of phenomenons as for us is to discover or perhaps rediscover into some celestial continuum that heralds of profound change as pointed the construction’s that make available the vanquishing corpses of times generations, and finding our place of universal understanding into the unformidable presence awaiting to the future.
But least of another day, the acceptance of continental drift, or plate tectonics theory. Canadian geophysicist J. Tuzo Wilson, a architects of modern geologic thought, summarized compelling evidence that the earth’s crust is a dynamic assembly of moving plates whose interactions explain most geological phenomena, including volcanoes and earthquakes. Wilson explained the existence of a continuous, planetwide system of plate boundaries, evidenced by ridges on the ocean floor. As he predicted, the study of the ocean floors verified the theory of continental drift within a few years of this article. Wilson’s suggestions that slow convection currents within the earth’s interior drive the motions of the plates are still being debated.
Beneath the oceans the crust consists of a single layer of dense, dark basaltic rock made up, in large part, of iron-magnesium minerals. On the continents, this layer is buried beneath a much thicker layer of lighter coloured, less dense rocks made up of aluminosilicate minerals. Because of the difference in density, the lighter rocks “float” on the basaltic ones. By a principle known as isostasy, in those areas where the lighter rocks rise highest - such as the great mountain ranges - they also extends downward to greater depths; beneath these ranges, roots of light rocks extend downward into the dark rocks of the crust to depths that are appreciably greater than under the vast, flat plains that occupy the interior regions of most continents.
In the 1960s geologists began to uncover proof that the continents not only float—that is, move up and down within the crust—but that they also travel, or drift, laterally. The study of the history and origins of continental drift is called plate tectonics because, in charting the directions that the continents have taken, geologists discovered that the earth's crust and upper mantle are divided into several of semirigid plates, each of which has recognizable boundaries and moves as a unit. Some of these tectonic plates (the Pacific plate, for example) consist almost entirely of oceanic crust; others, such as the North American and Eurasian plates, are made up of mostly continental crust. Plate boundaries are generally moved to midocean or close offshore, but in a few places rise from the seabottom and extend across dry land. Western California, where the earthquake-prone San Andreas fault marks the boundary between the Pacific and North American plates, is one such place.
The land-sea patterns of today have evolved during hundreds of millions of years, during which time continental landmasses drifted, were united by collisions, then torn apart and recombined. These movements show no sign of slackening or abating, so the distribution of sea and dry land will continue to change for if the planet contains the heat energy required to drive the movement of its crustal plates.
Plate Tectonics, is the theoretical hypothesis acceding to advance the underlying regional orientations that state such that the outer shell of the earth is made up of thin, rigid plates that move compared with each other. The theory of plate tectonics was formulated during the early 1960s, and it revolutionized the field of geology. Scientists have successfully used it to explain many geological events, such as earthquakes and volcanic eruptions and mountain building and the formation of the oceans and continents
Plate tectonics arose from an earlier theory proposed by German scientist Alfred Wegener in 1912. Looking at the shapes of the continents, Wegener found that they fit together like a jigsaw puzzle. Using this observation, along with geological evidence he found on different continents, he developed the theory of continental drift, which states that today’s continents were once joined into one large landmass.
Geologists of the 1950s and 1960s found evidence supporting the idea of tectonic plates and their movement. They applied Wegener’s theory to various aspects of the changing earth and used this evidence to confirm continental drift. By 1968 scientists integrated most geologic activities into a theory called the New Global Tectonics, or more commonly, Plate Tectonics.
Tectonic plates are made of either oceanic or continental crust and the very top part of the mantle, a layer of rock inside the earth. This crust and upper mantle form what is called the lithosphere. Under the lithosphere lies a fluid rock layer called the asthenosphere. The rocks in the asthenosphere move in a fluid manner because of the high temperatures and pressures found there. Tectonic plates are able to float upon the fluid asthenosphere because they are made of rigid lithosphere. See also Earth: Plate Tectonics.
The earth’s solid surface is about 40 percent continental crust. Continental crust is much older, thicker and less dense than oceanic crust. The thinnest continental crust, between plates that are moving apart, is about 15 km (about 9 mi) thick. In other places, such as mountain ranges, the crust may be as much as 75 km (47 mi) thick. Near the surface, it is composed of rocks that are felsic (made up of minerals including feldspar and silica). Deeper in the continental crust, the composition is mafic (made of magnesium, iron, and other minerals).
Oceanic crust makes up the other 60 percent of the earth’s solid surface. Oceanic crust is, usually, thin and dense. It is constantly being produced at the bottom of the oceans in places called mid-ocean ridges—undersea volcanic mountain chains formed at plate boundaries where there is a build-up of ocean crust. This production of crust does not increase the size of the earth, so the material produced at mid-ocean ridges must be recycled, or consumed, somewhere else. Geologists believe it is recycled back into the earth in areas called subductions zones, where one plate sinks underneath another and the crust of the sinking plate melts back down into the earth. Oceanic crust is continually recycled so that its age is generally not greater than 200 million years. Oceanic crust averages between five and 10 km (between three and 6 mi) thick. It is composed of a top layer of sediment. A middle layer of rock called basalt, and a bottom layer of a rock-called gabbro. Both basalt and gabbros are dark-coloured igneous, or volcanic, rocks.
Currently, there are seven large and several small plates. The largest plates include the Pacific plate, the North American plate, the Eurasian plate, the Antarctic plate, and the African plate. Smaller plates include the Cocos plate, the Nazca plate, the Caribbean plate, and the Gorda plate. Plate sizes vary a great deal. The Coco’s plate is 2000 km (1400 mi) wide, while the Pacific plate is the largest plate at nearly 14,000 km (nearly 9000 mi) wide.
Geologists study how tectonic plates move compared with a fixed spot in the earth’s mantle and how they move about each other. The first type of motion is called absolute motion, and it can lead to strings of volcanoes. The second kind of motion, called relative motion, leads to different types of boundaries between plates: plates moving apart from one another form a divergent boundary, plates moving toward one another form a convergent boundary, and plates that slide along one another form a transform plate boundaries. In rare instances, three plates may meet in one place, forming a triple junction. Current plate movement is making the Pacific Ocean smaller, the Atlantic Ocean larger, and the Himalayan mountains taller.
Geologists discovered absolute plate motion when they found chains of extinct submarine volcanoes. A chain of dead volcanoes forms as a plate moves over a plume, a source of magma, or molten rock, deep within the mantle. These plumes stay in one spot, and each one creates a hot spot in the plate above the plume. These hot spots can form into a volcano on the surface of the earth. An active volcano shows a hot spot as well as the youngest region of a volcanic chain. As the plate moves, a new volcano forms in the plate over the place where the hot spot occurs. The volcanoes in the chain get progressively older and become extinct as they move away from the hot spot. Scientists use hot spots to measure the speed of tectonic plates about a fixed point. To do this, they figure out the age of extinct volcanoes and their distance from a hot spot. They then use these numbers to calculate how far the plate has moved in the time since each volcano formed. Today, the plates move at velocities up to 18.5 cm per year (7.3 in per year). On average, they move nearly four to 7 cm per year (two to three in per year).
Divergent plate boundaries occur where two plates are moving apart from each other. When plates break apart, the lithosphere thins and ruptures to form a divergent plate boundary. In the oceanic crust, this process is called seafloor spreading, because the splitting plates are spreading apart from each other. On land, divergent plate boundaries create rift valleys - deep valley depressions formed as the land slowly splits apart.
When seafloor spreading occurs, magma, or molten rock material, rises to the sea floor surface along the rupture. As the magma cools, it forms new oceanic crust and lithosphere. The new lithosphere is less dense, so it rises, or floats, higher above older lithosphere, producing long submarine mountain chains known as mid-ocean ridges. The Mid-Atlantic Ridge is an underwater mountain range created at a divergent plate boundary in the middle of the Atlantic Ocean. It is part of a worldwide system of ridges made by seafloor spreading. The Mid-Atlantic Ridge is currently spreading at a rate of 2.5 cm per year (one in per year). The mid-ocean ridges today are 60,000 km (about 40,000 mi) long, forming the largest continuous mountain chain on earth. Earthquakes, faults, underwater volcanic eruptions, and vents, or openings, along the mountain crests produce rugged seafloor features, or topography.
Divergent boundaries on land cause rifting, in which broad areas of land are uplifted, or moved upward. These uplift and faulting along the rift result in rift valleys. Examples of rift valleys are found at the Krafla Volcano rift area in Iceland as well as at the East African Rift Zone - part of the Great Rift Valley that extends from Syria to Mozambique and out to the Red Sea. In these areas, volcanic eruptions and shallow earthquakes are common.
Convergent plate boundaries occur where plates are consumed, or recycled back into the earth’s mantle. There are three types of convergent plate boundaries: between two oceanic plates, between an oceanic plate and a continental plate, and between two continental plates. Subductions zones are convergent regions where oceanic crust is thrust below either oceanic crust or continental crust. Many earthquakes occur at subductions zones, and volcanic ridges and oceanic trenches form in these areas.
In the ocean, convergent plate boundaries occur where an oceanic plate descends beneath another oceanic plate. Chains of active volcanoes develop 100 to 150 km (60 to 90 mi) above the descending slab as magma rises from under the plate. Also, where the crust slides down into the earth, a trench forms. Together, the volcanoes and trench form an intra-oceanic islands arc and trench system. A good example of such a system is the Mariana Trench system in the western Pacific Ocean, where the Pacific plate is descending under the Philippine plate. In these areas, earthquakes are frequent but not large. Stress in and behind the arc often causes the arc and trench system to move toward the incoming plate, which opens small ocean basins behind the arc. This process is called back-arc seafloor spreading.
Convergent boundaries that occur between the ocean and lands create continental margin arc and trench systems near the margins, or edges, of continents. Volcanoes also form here. Stress can develop in these areas and cause the rock layers to fold, leading to earthquake faults, or breaks in the earth’s crust called thrust faults. The folding and thrust faulting thicken the continental crust, producing high mountains. Many of the world’s large destructive earthquakes and major mountain chains, such as the Andes Mountains of western South America, occur along these convergent plate boundaries.
When two continental plates converge, the incoming plate drives against and under the opposing continent. This often affects hundreds of miles of each continent and, at times, doubles the normal thickness of continental crust. Colliding continents cause earthquakes and form mountains and plateaus. The collision of India with Asia has produced the Himalayan Mountains and Tibetan Plateau.
A transform plate boundaries. Also, known as a transform fault system, forms as plates slide past one another in opposite directions without converging or diverging. Early in the plate tectonic revolution, geologists proposed that transform faults were a new class of fault because they “transformed” plate motions from one plate boundary to another. Canadian geophysicist J. Tuzlo Wilson studied the direction of faulting along fracture zones that divide the mid-ocean ridge system and confirmed that transform plate boundaries were different from convergent and divergent boundaries. Within the ocean, transform faults are usually simple, straight fault lines that form at a right angle to ocean ridge spreading centres. As plates slide past each other, the transform faults can divide the centres of ocean ridge spreading. By cutting across the ridges of the undersea mountain chains, they create steep cliff slopes. Transform fault systems can also connect spreading centres to subductions zones or other transform fault systems within the continental crust. As a transform plate boundary cuts perpendicularly across the edges of the continental crust near the borders of the continental and oceanic crust, the result is a system such as the San Andreas transforms fault system in California.
Rarely, a group of three plates, or a combination of plates, faults, and trenches, meet at a point called a triple junction. The East African Rift Zone is a good example of a triple plate junction. The African plate is splitting into two plates and moving away from the Arabian plate as the Red Sea meets the Gulf of Aden. Another example is the Mendocino Triple Junction, which occurs at the intersection of two transform faults (the San Andreas and Mendocino faults) and the plate boundary between the Pacific and Gorda plates.
Plate movement is changing the sizes of our oceans and the shapes of our continents. The Pacific plate moves at an absolute motion rate of 9 cm per year (four in per year) away from the East Pacific Rise spreading centre, the undersea volcanic region in the eastern Pacific Ocean that runs parallel to the western coast of South America. On the other side of the Pacific Ocean, near Japan, the Pacific plate is being subducted, or consumed under, the oceanic arc systems found there. The Pacific Ocean is getting smaller as the North and South American plates move west. The Atlantic Ocean is getting larger as plate movement causes North and South America to move away from Europe and Africa. Since the Eurasian and Antarctic plates are nearly stationary, the Indian Ocean right now is not significantly expanding or shrinking. The plate that includes Australia is just beginning to collide with the plate that forms Southeast Asia, while India’s plate is still colliding with Asia. India moves north at 5 cm per year (two in per year) as it crashes into Asia, while Australia moves farther away from Antarctica each year.
Although plate tectonics has explained most of the surface features of the earth, the driving force of plate tectonics is still unclear. According to geologists, a model that explains plate movement should include three forces. Those three forces are the pull of gravity; convection currents, or the circulating movement of fluid rocky material in the mantle; and thermal plumes, or vertical columns of molten rocky material in the mantle.
Geologists believe that tectonic plates move primarily as a result of their own weight, or the force of gravity acting on them. Since the plates are denser than the underlying asthenosphere, they tend to sink. Their weight causes them to slide down gentle gradients, such as those formed by the higher ocean ridge crests, to the lower subductions zones. Once the plate’s leading edge has entered a subductions zone and penetrated the mantle, the weight of the slab itself will tend to pull the rest of the plate toward the trench. This sinking action is known as slab-pull because the sinking plate edge pulls the remainder of the plate behind it. Another kind of action, called ridge-push, is the opposite of slab-pull, in that gravity also causes plates to slide away from mid-ocean ridges. Scientists believe that plates pushing against one another also causes plate movement.
In 1929 British geologist Arthur Holmes proposed the idea of convection currents - the movement of molten material circulating deep within the earth - and the idea was modified to explain plate movement. A convection current occurs when hot, molten, rocky material floats up within the asthenosphere, then cools as it approaches the surface. As it cools, the material becomes denser and begins to sink again, moving in a circular pattern. Geologists once thought that convection currents were the primary driving force of plate movement. They now believe that convection currents are not the primary cause, but are an effect of sinking plates that contributes to the overall movement of the plates.
Some scientists have proposed the idea of thermal plumes, vertical columns of molten material, as an additional force of plate movement. Thermal plumes do not circulate like convection currents. Preferably, they are columns of material that rise through the asthenosphere and appear on the surface of the earth as hot spots. Scientists estimate thermal plumes to be between 100 and 250 km (60 and 160 mi) in diameter. They may originate within the asthenosphere or even deeper within the earth at the boundary between the mantle and the core.
Scientists have also observed tectonic activity and fracturing on several moons of other planets in our solar system. Starting in 1985, images from the Voyager probes showed that Saturn’s satellite Enceladus and Uranus’ moon Miranda also show signs of being tectonically active. In 1989 the Voyager probes sent photographs and data to Earth of volcanic activity on Neptune’s satellite Triton. In 1995 the Galileo probe began to send data and images of tectonic activity on three of Jupiter’s four Galilean satellites. The information that scientists gather from space missions such as these helps increase their understanding of the solar system and our planet. They can apply this knowledge to understand the forces better that created the earth and that continues to act upon it.
Scientists believe that Enceladus has a very tectonically active surface. It has several different terrain types, including craters, plains, and many faults that cross the surface. Miranda has fault canyons and terraced land formations that indicate a diverse tectonic environment. Scientists studying the Voyager 2 images of Triton found evidence of an active geologic past as well as ongoing eruptions of ice volcanoes.
Scientists are still gathering information from the Galileo probe of the Jupiter moon system. Three of Jupiter’s four Galilean satellites show signs of being tectonically actively. Europa, Ganymede, and Io all exhibit various features that indicate tectonic motion or volcanism. Europa’s surface is broken apart into large plates similar to the plates found on Earth. The plate movement indicates that the crust is brittle and that the plates move over the top of a softer, more fluid layer. Ganymede probably has a metallic inner core and at least two outer layers that make up a crust and mantle. Io may also have a giant iron core interior that causes the active tectonics and volcanism. It is believed that Io has a partially molten rock mantle and crust.
The theory of plate tectonics arose from several previous geologic theories and discoveries. As early as the 16th century, explorers began examining the coastlines of Africa and South America and proposed that these continents were once connected. In the 20th century, scientists proposed theories that the continents moved or drifted apart from each other. Additionally, in the 1950s scientists proposed that the earth’s magnetic poles wander, leading to more evidence, such as rocks with similar magnetic patterns around the world, that the continents had drifted. More recently, scientists examining the seafloor have discovered that it is spreading as new seafloor is created, and through this work they have discovered that the magnetic polarity of the earth has changed several times throughout the earth's history. The theory of plate tectonics revolutionized earth sciences by providing a framework that could explain these discoveries, as well as events such as earthquakes and volcanic eruptions, mountain building and the formation of the continents and oceans. See also Earthquake.
Beginning in the late 16th century and early 17th century, many people, including Flemish cartographer Abraham Ortelius and English philosopher Sir Francis Bacon, were intrigued by the shapes of the South American and African coastlines and the possibility that these continents were once connected. In 1912, German scientist Alfred Wegener eventually developed the idea that the continents were at one time connected into the theory of continental drift. Scientists of the early 20th century found evidence of continental drift in the similarity of the coastlines and geologic features on both continents. Geologists found rocks of the same age and type on opposite sides of the ocean, fossils of similar animals and plants, and similar ancient climate indicators, such as glaciation patterns. British geologist Arthur Holmes proposed that convection currents drove the drifting movement of continents. Most earth scientists did not seriously consider the theory of continental drift until the 1960s when scientists began to discover other evidence, such as polar wandering, seafloor spreading, and reversals of the earth’s magnetic field.
In the 1950s, physicists in England became interested in the observation that certain kinds of rocks produced a magnetic field. They soon decided that the magnetic fields were remnant, or left over, magnetism acquired from the earth’s magnetic field as the rocks cooled and solidified from the hot magma that formed them. Scientists measured the orientation and direction of the acquired magnetic fields and, from these orientations, calculated the direction of the rock’s magnetism and the distance from the place the rock was found to the magnetic poles. As calculations from rocks of varying ages began to accumulate, scientists calculated the position of the earth’s magnetic poles over time. The position of the poles varied depending on where the rocks were collected, and the idea of a polar wanders the path began to form. When sample paths of polar wander from two continents, such as North America and Europe, were compared, they coincided as if the continents were once joined? This new science and methodology became known as the discipline of paleomagnetism. As a result, discussion of the theory of continental drift increased, but most earth scientists remained skeptical.
During the 1950s, as people began creating detailed maps of the world’s ocean floor, they discovered a mid-ocean ridge system of mountains nearly 60,000 km (nearly 40,000 mi) long. This ridge goes all the way around the globe. American geologist Harry H. Hess proposed that this mountain chain was the place where a new ocean floor was created and that the continents moved as a result of the expansion of the ocean floors. This process was termed seafloor spreading by American geophysicist Robert S. Dietz in 1961. Hess also proposed that since the size of the earth seems to have remained constant, the seafloor must also be recycled back into the mantle beneath mountain chains and volcanic arcs along the deep trenches on the ocean floor.
These studies also found marine magnetic anomalies, or differences, on the sea floor. The anomalies are changes, or switches, in the north and south polarity of the magnetic rock of the seafloor. Scientists discovered that the switches make a striped pattern of the positive and negative magnetic anomalies: one segment, or stripe, is positive, and the segment next to it is negative. The stripes are parallel to the mid-ocean ridge crest, and the pattern is the same on both sides of that crest. Scientists could not explain the cause of these anomalies until they discovered that the earth’s magnetic field periodically reverses direction.
In 1963, British scientist’s Fred J. Vine and Drummond H. Matthews combined their observations of the marine magnetic anomalies with the concept of reversals of the earth’s magnetic field. They proposed that the marine magnetic anomalies were a “tape recording” of the spreading of the ocean floor as the earth’s magnetic field reversed its direction. At the same time, other geophysicists were studying lava flows from many parts of the world to see how these flows revealed the record of reversals of the direction of the earth’s magnetic field. These studies showed that nearly four reversals have occurred over the past five million years. The concept of magnetic field reversals was a breakthrough that explained the magnetic polarity switches seen in seafloor spreading as well as the concept of similar magnetic patterns in the rocks used to demonstrate continental drift.
The theory of plate tectonics tied together the concepts of continental drift, polar wandering, seafloor spreading, and magnetic field reversals into a single theory that completely changed the science of geology. Geologists finally had one theory that could explain all the different evidence they had accumulated to support these previous theories and discoveries. Geologists now use the theory of plate tectonics to integrate geologic events, to explain the occurrence of earthquakes and volcanic eruptions, and to explain the formation of mountain ranges and oceans.
The Ice Ages, were the periods in Earth’s history when sea ice or glaciers have covered a significant portion of the planet’s surface and significant cooling of the atmosphere has occurred. Earth has existed for about 4.5 billion years. During that time it has experienced several ice ages, each lasting tens of millions of years. The total of these episodes may account for as much as 15 to 20 percent of the planet’s history. The icy cover has ranged from about 10 percent to about 30 percent of the entire surface of the planet.
The most recent ice age, the Pleistocene Epoch, lasted from about 1.6 million years to 10,000 years before present. During that time at least 20 glaciations, or periods when the ice cover increased, occurred. Each of these periods was followed by an interglaciation, or a period when the ice cover shrank. The most recent glaciation in North America, called the Wisconsin glaciation, lasted from about 115,000 years ago to 10,000 years ago. The climate during that time was much different from what it is today, with temperatures on the continents as much as 15° C (27° F) colder. In areas that are currently occupied by subtropical deserts, cooler and wetter climates caused large lakes to form from increased rainfall and glacial runoff. The past 10,000 years have been part of a warm interglacial period. However, the presence of massive continental ice sheets on Greenland and Antarctica, along with numerous smaller glaciers in mountainous regions throughout the world, indicates that Earth is still in the grip of an ice age.
Glacial geologists can determine where ancient glaciers were located by studying the land. They examine the processes of glacial action to learn more about the impact glaciers have had, and continue to have, on Earth. Geologic features, such as glacial lakes, form when glaciers expand. Expanding glaciers also cause sea levels to decrease. Glacial erosion (wearing away) and glacial deposition (release of sediments) causes many geologic changes. Scientists study these processes, and ice cores from glaciers and sediment cores from lakes and oceans, to learn about ice ages that predate the Pleistocene Epoch. Scientists use these findings to determine what factors may influence the occurrence of future ice ages.
During an ice age several geologic changes occur. These alterations range from changes in the shape of the land to a decrease in sea level. Water freezes and settles within the growing glaciers. This process causes worldwide sea level to drop by as much as 150 m. (500 ft.) below the current sea level. When this process occurs, shallow ocean waters that cover the continental shelves, or the edges of the continents, recede and uncover the submerged land. Advancing ice sheets can block water drainage pathways and create glacial lakes. Elsewhere, rivers are diverted from their original pathways to courses along the ice margin. The added weight of glacial ice sheets causes Earth's crust to lower by as much as several hundred metres. The ground in some areas becomes frozen throughout the year and forms permafrost, or permanently frozen ground. When glaciers recede, the combined effects of rebound from crustal depression and the shifting of ice masses cause the redistribution of rivers and lakes.
Geologists study glacial erosion to determine the structure of former glaciers and to examine current glaciers. The freezing and thawing processes of glacial erosion loosen bedrock underneath and next to glaciers. The unsecured rock pieces may be carried away within the flowing ice or may be dragged along the bottom of the glacier and scratch the surface of the land. In mountainous regions, glaciers transform V-shaped river valleys into deeper and broader U-shaped valleys by erosion. Glacial erosion at the highest altitudes creates bowl-shaped hollows (cirques) at the heads of valleys. A series of peaks (horns) and narrow ridges (arêtes) are all that remain of once broad uplands.
Geologists also study features made from glacial deposits, called glacially till. Ridges made of glacial till, called moraines (from the French morena, or mound), offers the most important clues to the exact locations of former glaciers. Moraines are formed by the broken-down particles of rocks that ice flows have put into attributive significations the glacier margin (terminus), where the material is released from the ice and form deposits. When glacial ice melts, the ice flow deposits particles ranging in size from the smallest clay grains to boulders as large as 10 m (30 ft) across. The ice flows may deposit the glacial till in a thin, flat sheet beneath a glacier or into a series of elongated hills called drumlins moulded beneath the flowing ice. Moraines may be more than 100 m (300 ft) high and
5 km (3 mi) broad. As a glacier shrinks because of climatic change, recessional moraines form around each successive position of the ice margin. Other deposits include glacial outwash, composed of sand and gravel deposited by glacial runoff streams.
Geologists often examine sediment cores to learn about glaciation and climate fluctuation. These scientists take core samples to study sediment layers that provide a continuous, undisturbed record of past ice ages. They acquire these samples from the ocean floor, from lakes, or as ice cores from glaciers.
The evidence for the earliest ice age dates to about 2.3 billion years ago. The combined marine and land records indicate that several pre - Pleistocene ice ages occurred. Most features of earlier ice ages have been buried or eroded away over time by surface geologic processes. Most of the glacial landforms and deposits visible today are the results of the most recent (Wisconsin) glaciation. Some ancient glacial features partially survived erosion, and ancient glacial till deposits that also withstood erosion changed into rock. These till deposits, or tillites, provide the best evidence of the age and distribution of ancient ice ages.
Tillites from Ontario and elsewhere in North America may have been formed from the same glaciation that deposited tillites in South Africa and possibly Australia. These tillites are evidence of one of the first ice ages, which occurred more than 950 million years ago. The next ice age occurred between 950 and 600 million years ago, and included at least three separate glacial - interglacial intervals. These continental glaciations were widespread and included western North America and portions of South America, Africa, and Australia. Another expansion of continental ice, between 450 and 400 million years ago, was entered northern Africa and spread to adjacent portions of northern Europe and South America. Between 330 and 240 million years ago, an extensive glaciation affected Africa, Antarctica, Australia, Asia, and South America. Despite evidence for the widespread distribution of this glaciation, smaller, localized icecaps were probably more common than massive continental ice sheets. This is because during this time sea level fluctuated only slightly, rather than the 130 m (430 ft) or more of fluctuation that would be expected if great volumes of ice alternately formed and melted.
The record of previous glacial activity is the best indicator for future ice ages. Scientists examine the evidence for the numerous 100,000-year glacial-interglacial cycles within the present ice age to attempt a forecast of future ice ages. Since all previous ice ages lasted tens of millions of years, our present ice age will likely continue for a considerable amount of time. Each glaciation begins slowly and may take 80,000 years or more to reach its maximum extent. A rapid melting of these expanded glaciers within just a few thousand years follows. Then the next glaciation begins to build, only 10,000 to 20,000 years after the maximum of the previous glaciation occurred. Evidence from both lands and sea environments indicates that, at least before the human-induced global warming of the last two centuries, the worldwide climate has been cooling naturally for several thousand years. Ten thousand years have already passed since the end of the last glaciation, and 18,000 years have passed since the last maximum. This may indicate that Earth has entered the beginning of the next worldwide glaciation.
Several possible causes of ice ages exist. Scientists have proposed numerous theories to explain their occurrence. In the 1920s Yugoslav scientist Milutin Milankovitch proposed the Milankovitch Astronomical Theory, which state’s climatic fluctuations and the onset of glaciation can be caused by variations in Earth’s position relative to the Sun. Milankovitch calculated that this deviation of Earth’s orbit from its almost circular path occurs every 93,408 years. The movement of Earth’s crustal plates, called plate tectonics, is also linked to the occurrence of ice ages. The positions of the plates in polar regions may contribute to ice ages. Changes in global sea level may affect the average temperature of the planet and lead to cooling that may cause ice ages. Other theories explaining the causes of ice ages—such as significant variations in the heat output of the Sun, the presence of an interplanetary dust cloud that occasionally blocks some Sun's heat from reaching Earth, and meteorite impacts—have not yet been supported by any solid evidence.
The Milankovitch Astronomical Theory best explains regular climatic fluctuations. The theory is based on three variations in the position of Earth relative to the Sun: the eccentricity (elongation or circularity of the shape) of Earth's orbit, the tilt of Earth's axis toward or away from the Sun, and the degree of wobble of Earth's axis of rotation. The total effect of these changes causes one region of Earth—latitude 60° to 70° north, near the Arctic Circle—to receive low amounts of summer radiation about once every 100,000 years. These cool summer periods last several hundred to several thousand years and thus provide sufficient time to allow snowfields to expand and merge into glaciers in this area, signalling the beginning of a glaciation.
When glaciers expand during an ice age, the sea level drops because the water that forms glaciers ultimately comes from the oceans. Global sea level affects the overall temperature of the planet because solar radiation, or heat, is better absorbed by water than by land. When sea levels are low, more land surfaces becomes exposed. Since the land is not able to absorb as much solar radiation as the water can, the overall average temperature of the planet decreases, or cools, and may contribute to the onset of an ice age.
A map showing Earth during an ice age would look very different from a map of the modern world. During the Wisconsin glaciation of 115,000 to 10,000 years ago, two ice sheets, the Laurentides and the Cordilleran, covered the northern two-thirds of North America, including most of Canada, with ice. Other parts of the world, including Eurasia and parts of the North Atlantic Ocean, were also blanketed in sheets of ice
The Laurentides continental ice sheet extended from the eastern edge of the Rocky Mountains to Greenland. The separate Cordilleran Ice Sheet was composed of mountain ice caps and valley glaciers that flowed onto the surrounding lowlands in parts of northern Alaska, in parts of the Sierra Nevada, and in the Cascade Range and the Rocky Mountains as far south as New Mexico. Where the continental shelf between Alaska and Siberia was uncovered, the Bering land bridge formed. In northern Eurasia, continental ice extended from Great Britain eastward to Scandinavia and Siberia. Separate mountains, and glacial systems covered the Alps, the Himalayas, and the Andes. The extensive ice sheets on Antarctica and Greenland did not expand very much during each glaciation. Sea ice grew worldwide, particularly in the North Atlantic Ocean.
Bringing us upon the Stone Age, of which this period of human technological development characterized by using stone as the principal raw material for tools. In a given geographic region, the Stone Age normally predated the invention or spread of metalworking technology. Human groups in different parts of the world began using stone tools at different times and abandoned stone for metal tools at different times. Broadly speaking, however, the Stone Age began roughly 2.5 million years ago, ended in some parts of the world 5,000 years ago, and ended in other regions much more recently. Today only a few isolated human populations rely largely on stone for their technologies, and that reliance is rapidly vanishing with the introduction of tools from the modern industrialized world.
Human ancestors living before the Stone Age likely used objects as tools, a behaviour that scientists find today among chimpanzees. Wild chimpanzees in Africa exhibit a range of tool-using behaviours. For example, they used bent twigs to fish for termites, chewed wads of leaves to soak up liquid, and branches and stones as hammers, anvils, missiles, or clubs. However, when prehistoric humans began to make stone tools they became dramatically distinct from the rest of the animal world. Although other animals may use stone objects as simple tools, the intentional modification of stone into tools, and using tools to make other tools, is behaviour unique to humans. This stone toolmaking and tool-using behaviour became central to the way early humans adapted to their environment and almost affected human evolution
Archaeologists believe the Stone Age began in the vicinity to 2.5 million years ago because that marks the age of the earliest stone tool remnants ever discovered. The earliest recognizable stone artifacts mark the beginnings of the archaeological record—that is, material remnants of ancient human activities. As recently as 5,000 years ago all human societies on the face of the earth were essentially still living in the Stone Age. Therefore, more than 99.8 percent of humans’ time as toolmakers—from 2.5 million years ago to 5,000 years ago - took places during the Stone Age. During the Stone Age our ancestors went through many different stages of biological and cultural evolution. It was long after our lineage became anatomically modern that we began to experiment with innovations such as metallurgy, heralding the end of the Stone Age.
The term Stone Age has been used since the early 1800s as a designation for an earlier, prehistoric stage of human culture, one in which stone rather than metal tools were used. By the early 1800s various archaeological sites had been excavated in Europe that contained mysterious items from evidently earlier, prehistoric times. Christian Thomsen, curator of the National Museum in Copenhagen, Denmark, developed a classification scheme to organize the museum’s growing collections into three successive technological stages in the human past: Stone Age, Bronze Age, and Iron Age. This three-age classification was quickly adopted and spread not only among museums in Europe but also among excavators, who can identify Stone Age remnants that were found below Bronze Age remnants, which were in turn found below Iron Age remnants as they dug down through layers of deposits at their sites. The fact that Stone Age remnants were found at the bottom layers indicated that they were the oldest
The study of the Stone Age falls under the fields of anthropology, which is the study of human life and culture from the origins of human life up to the present, and archaeology, which is the study of the material remains of humans and human ancestors. Archaeologists seek out, explore, and study archaeological sites, locations around the world where historic or prehistoric people left behind traces of their activities. Archaeologists use the data collected to make theories about how human ancestors lived.
Archaeologists normally use the term artifact to refer to objects modified by human action, either intentionally or unintentionally. The term tool is used to refer to something used by a human or a human ancestor for some purpose and may be modified or not. For instance, a thrown rock is a tool, even if it were not modified. It is usually difficult to demonstrate that a particular stone artifact was used as a tool prehistorically, so in practice, archaeologists prefer to use the term artifact instead, especially in relation to the earlier stages of the Stone Age. Unused debris or waste from the manufacture of stone tools is also considered artifactual.
Stone artifacts are important to archaeologists who study prehistoric humans, because they can yield a wide range of information about ancient peoples and their activities. Stone artifacts are, in fact, often the principal archaeological remnants that persist after the passage of time and as such can give important clues as to the presence or absence of ancient human populations in any given region or environment. Careful analysis of Stone Age sites can yield crucial information regarding the technology of prehistoric toolmakers, which in turn give anthropologists insight into the levels of cognitive (thinking) ability at different stages of human evolution.
During the Stone Age, Earth experienced the most recent in a succession of ice ages, in which glaciers and sea ice covered a large portion of Earth’s surface. The most recent ice age period lasted from 1.6 million to 10,000 years ago, a period of glacial and warmer interglacial stages known as the Pleistocene Epoch. The Holocene Epoch began at the end of the ice age 10,000 years ago and continued to the present time.
Early hominids made stone artifacts either by smashing rocks between a hammer and anvil (known as the bipolar technique) to produce usable pieces or by a more controlled process termed flaking, in which stone chips were fractured away from a larger rock by striking it with a hammer of stone or other hard material. Subsequently, during the lingering existence of say 10,000 years, the diversely in techniques for producing masonry artifacts - including pecking, grinding, sawing, and boring - became additionally familiar. The best rocks for flaking tended to be hard, fine-grained, or amorphous (having no crystal structure) rocks, including lava, obsidian, ignimbrite, flint, chert, quartz, silicified limestone, quartzite, and indurated shale. Ground stone tools could be made on a wider range of raw material types, including coarser grained rock such as granite.
Flaking produces several different types of stone artifacts, which archaeologists look forward to at prehistoric sites. The parent pieces of rock from which chips have been detached are called cores, and the chips removed from cores are called flakes. A flake that has had yet smaller flakes removed from one or more edges to sharpen or shape it is known as a retouched piece. The stone used to knock flakes from cores is called a hammerstone or a precursor. Other flaking artifacts include fragments and chunks, most of which are broken cores and flakes.
The terms culture and industries both refer to a system of technology (Toolmaking technique, for example) shared by different Stone Age sites of the same broad time. Experts now prefer to use the term industry instead of culture to refer to these shared Stone Age systems.
Archaeologists have divided the Stone Age into different stages, each characterized by different types of tools or tool-manufacturing techniques. The stages also imply broad time frames and are perceived as stages of human cultural development. The most widely used designations for the successive stages are Paleolithic (Old Stone Age), Mesolithic (Middle Stone Age), and Neolithic (New Stone Age). British naturalist Sir John Lubbock in 1865 defined the Paleolithic stage as the period in which stone tools were chipped or flaked. He defined the Neolithic as the stage in which ground and polished stone axes became prevalent. These two stages also were associated with different economic and subsistence strategies: Paleolithic peoples were hunter-gatherers while Neolithic peoples were farmers. Archaeologists subsequently identified a separate stage of stone tool working in Eurasia and Africa between the Paleolithic and the Neolithic, called the Mesolithic. This period is characterized by the creation of microliths, small, geometric-shaped stone artifacts attached to wood, antler, or bone to form implements such as arrows, spears, or scythes. Microliths began appearing between 15,000 and 10,000 years ago at the end of the Pleistocene Ice Age.
The Paleolithic/Mesolithic/Neolithic division system was first applied only to sites in Europe, but is now widely used (with some modification) to refer to prehistoric human development in much of Asia, Africa, and Australasia. Different terminology is often used to describe the cultural-historical chronology of the Americas, which humans did not reach until some point between 20,000 and 12,000 years ago. However, there is a general similarity, the transitional form of flaked stone tools are associated with prehistoric hunter-gatherers to both flaked and ground stone tools associated with the rise of early farming communities. The period in the Americas up to the end of the Pleistocene Ice Age about 10,000 years ago, when most humans were hunter-gatherers, is called Paleo-Indian and the subsequent, post-glacial period is known as Archaic.
Archaeologists subdivide the Paleolithic into the Lower Paleolithic (the earliest phase), Middle Paleolithic, and Upper Paleolithic (the later phase), based upon the presence or absence of certain classes of stone artifacts The Lower Paleolithic dates from approximately 2.5 million years ago until about 200,000 years ago. It includes the earliest record of human toolmaking and documents much of the evolutionary history of the genus Homo from its origins in Africa to its spread into Eurasia. Two successive toolmaking industries characterize the Lower Paleolithic: the Oldowan and the Acheulean.
The Oldowan industry was named by British Kenyan anthropologists Louis Leakey and Mary Leakey for early archaeological sites found at Olduvai Gorge in northern Tanzania. It is also sometimes called the chopper-core or pebble-tool industry. Simple stone artifacts made from small stones or blocks of stone characterize the Oldowan industry. Mary Leakey classified Oldowan artifacts as either heavy-duty tools or light-duty tools, as both their classifications deemed to be heavy-duty tools, which include core types such as choppers, discoids, polyhedrons, and heavy-duty scrapers. Many of these cores may have been produced to generate sharp-edged flakes, but some could have been used for chopping or scraping activities as well. Light-duty tools include retouched forms such as smaller scrapers, awls (sharp, pointed tools for punching holes in animal hides or wood), and burins (chisel-like flint tools used for engraving and cutting). Oldowan techniques of manufacture included hard-hammer percussion, or detaching flakes from cores with a stone hammer; the anvil technique, striking a core on a stationary anvil to detach flakes; and bipolar technique, detaching flakes by placing the core between an anvil and the hammerstone.
Early humans probably also made tools from a wide range of materials other than stone. For example, they probably used wood for simple digging sticks, spears, clubs, or probes, and they probably used shell, hide, bark, or horn to fashion containers. Unfortunately, organic materials such as these do not normally survive from earlier Stone Age times, so archaeologists can only speculate about whether such tools were used.
Two of the oldest Oldowan sites are in Ethiopia: Gona (occupied 2.5 million years ago) and Omo (2.3 million years ago). Other well-studied Oldowan sites include Lokalalei (2.3 million years ago) and Koobi Fora (1.9 million to 1.4 million years ago), in Kenya; Olduvai Gorge (1.9 million to 1.2 million years ago), in Tanzania; Ain Hanech (perhaps 1.7 million years ago), in Algeria. The cave deposits at Sterkfontein and Swartkrans (estimated to be from 2.0 million to 1.5 million years ago), in South Africa.
Theories about the intelligence and culture of prehistoric man are beginning to be drastically revised. Accumulated evidence now depicts European men living between 100,000 and 10,000 years ago as communal men who were skilled hunters and toolmakers, who had developed formal burial rites for members of their tribes and ritual burials for animals, who had some belief in an afterlife, who took excellent care of their sick and elderly, and who, in their heyday, carried around pocket-sized calendars of their own making.
A ten-member international expedition, led by Ralph S. Solecki of Columbia University, found the bones of a dismembered deer ritually buried by Neanderthal men about 50,000 years ago. The bones of the deer's foot, jaw, and back, its shoulder blades, and the top of its skull were found buried 5 feet deep in the Nahr Ibrahim Cave, north of Beirut, Lebanon. The presence of the skull, the bed of stones on which the bones were placed, and the red-earth colouring of the bones, which was not native to the cave, indicated that a ritual known as hunters' magic was involved in the burial. Solecki interpreted the burial as an attempt "to ensure a successful hunt by the ceremonial treatment of one of the animals." Although evidence existed showing that bears were ritually treated by Neanderthal men, this was the first discovery of a lone deer buried in this manner.
An American expedition, also led by Solecki, excavated a mountain cave near Shanidar in Iraqui Kurdistan and discovered evidence that Neanderthals practiced a form of religious burial suggesting a belief in an afterlife: at least one of the nine skeletons uncovered in the cave was buried with flowers. Also found in the cave was the skeleton of a man of about 40, comparable to a modern age of 80, who had been born with a deformed right arm. A Neanderthal doctor had skilfully amputated the arm above the elbow, and judging by his death at a ripe old age, the man was carefully cared for from his boyhood until he died as a result of a rockfall inside the cave, a common peril at that time.
Recent paleontological examinations of skeletons suggest that the Neanderthals' stooped posture was the result of a vitamin D deficiency. Lack of sunlight during the Ice Age might have caused their upright posture to become deformed by rickets.
In January it was revealed that a fairly sophisticated system of notation charting the phases of the moon was used throughout most of Europe during the last Ice Age, beginning about 34,000 years ago. Marks such as scratches and notches on pieces of bones, antlers, and stone, previously regarded as decorations, were shown to be representations of the lunar calendar. Alexander Marshack, a research associate at the Peabody Museum of Archaeology and Ethnology at Harvard University, began investigating the markings in 1964 and published the results of his study this year in France. The inscribed objects he studied represented all cultural levels from 34,000 to 10,000 years ago. All were pocket-sized, and as many as 24 tools were used to cut a single sequence, some covering a year or more. This system of notation seems to anticipate the development of a calendar, the concept of number, and the use of abstract symbols. It had been thought that such cognitive abilities developed only after the start of an agricultural society, less than 10,000 years ago.
A tribe of about 24 people living a Stone Age way of life was found in the Tasaday Forest on the southern Philippines' Mindanao Island in July. Anthropologists speculate that the tribe has been cut off from the rest of the world for at least 400 years and maybe as much as 2,000 years.
The tribe was first discovered five years ago by an official conducting a census survey. He described the finding a tribe of "jungle people so mysterious that they were known only as the bird who walks the forest like the wind." A long search led to the Tasaday. Interpreters at first had trouble understanding the tribe's language, which is related to Manubo, a native Filipino tongue in the Malayo-Polynesian family.
As communication became easier, it was found that the tribe calls itself the Tasaday because "the man who owns the forest in which they live told their ancestors in a dream to call themselves Tasadays, after a mountain." When asked whether they had ever been off the island, the Tasadays replied that they did not know leaving was possible; in fact, it was found that they had never even seen the ocean. The Tasadays are monogamous in mating but communal in all other ways, have no leader, know no other tribe, have known no unfriendly people, and have never heard of fighting.
The Tasadays do not cultivate food but never ventures far from their clearing; food is easily found in the lush vegetation of the forest in which they live. The staple of their diet is the pith of the wild palm. To supplement this, they catch tadpoles and small fish with their hands from the nearby streams. Monkey meat is considered a delicacy. After the monkey's hair is singed in a fire and cut away with bamboo blades sharpened by small stones, the meat is roasted.
The group includes six families with 13 children, nine of whom are boys. All matters of mutual concern, such as food gathering, are decided in an open meeting.
New information about the Mayan civilization, the most highly developed civilization in the New World before the arrival of the white man, was gained from the discovery of a 11-page codex fragment of a Mayan calendar book. (A codex is a manuscript copy of an ancient text.) The fragment is said to be part of a larger book about 20 pages long. The three other known codices were brought to Europe during the Spanish conquest but did not emerge as important historical material until the 1900's. The newly discovered codex is the first to be found in over a century.
Composed of bark cloth, like the other three, the 11-page codex is expected to reveal "pictorial information on the Venus calendar and its influence on Mayan religion and astrology," according to Michael D. Coe, professor of anthropology at Yale University. The fragment dates to the late Mayan period, between 1400 and 1500. The new fragment reveals that the Mayans viewed all four phases of the Venus cycle as threatening. Previously, only the first phase was thought to have been considered sinister.
All four cycles of Venus as seen from the earth were measured by Mayan priests, who calculated that each cycle took 584 days to be completed. Modern astronomers calculate 583.92 days for each complete cycle. The complete 20-page codex would have covered 65 Venus cycles.
Coe believes the fragment to be authentic "because it is on bark cloth, [because of] the condition of the fragment, the fact that none of the pictorial material duplicates or imitates anything we know about the Venus calendar, and, lastly, because no forger could be clever enough to invent material displaying so much knowledge of Mayan life."
Early Slavic tribes formed an organized state in the fourth to sixth centuries, about 500 years earlier than was believed, according to evidence reported in Tass, the Soviet press agency. Arkady Bugai, the Ukrainian archaeologist credited with the discovery, based his conclusion on radiocarbon dating of charred wood found in the remains of the so-called Serpentine Wall, a 500-mile complex of defensive earthenworks that once ringed the present site of Kiev, the Ukrainian capital. The charred wood used in the radiocarbon tests was from what is believed to be the remains of trees burned to clear ground for the wall. Bugai reasoned that a highly organized state was required to move the seven billion cubic feet of earth that made up the wall, which rises to a height of 30 to 35 feet and is 50 feet wide at its base.
The Serpentine Wall, which enclosed a roughly triangular area, was assumed to have been built to defend the Kiev area from hostile tribes. Ukrainian scholars now believe that the area must have had a population of approximately one million people during the time of the construction. It was formerly believed that the first consolidation of Russian tribes occurred around the tenth century, during the rise of Kievan Russia.
An expedition bent on disproving the theory that the American man came to North America by crossing a land bridge over what is now the Bering Strait began in September. Gene Savoy, the American explorer who is known for his 1964 discovery of the ruined Inca city of Vilcabamba in Peru, believes that American man originated in the jungles east of the Andes Mountains in South America, where he thinks advanced civilizations flourished as long ago as 1500 BC. The discovery of a new species of human ancestors and of fossils of the oldest human beings yet to be found in Europe dominated the news in anthropology in 1995.
The discovery of fossils of a new species of human ancestors — Australopithecus anamensis - at sites near Lake Turkana in Kenya was announced in August. Anamensis, a small-brained upright walker resembling the famous Lucy skeleton (identified with the species’ Australopithecus afarensis), weighed about 110 pounds. The complete upper and lower jaws, a set of lower teeth, a skull fragment, the teeth of several individuals, and a shinbone were dated to between 4.1 million and 3.9 million years ago, according to Meave Leakey (wife of Richard Leakey), one of the lead researchers.
Anamensis, the researchers indicated, may be directly ancestral to later afarensis (dated at 3.6 million years old). The shinbone is the oldest direct evidence yet discovered for upright, a bipedal locomotion (the ability to walk upright on two legs), a defining trait of humans. The earliest known evidence before this was the tracks (3.7 million years old) of three humanlike individuals, probably australopithecines, who strolled across a bed of fresh volcanic ash in what is now Laetoli, Tanzania.
The relationship between anamensis (from anam, a native Kenyan term for "lake") and an even older species whose discovery was announced in 1994 was unclear. The older species, found in the Middle Awash region of Ethiopia, was first named Australopithecus ramidus. The genus name was later changed to Ardipithecus ("ground apes"). The teeth and scanty bone fragments of Ardipithecus ramidus were dated at 4.4 million years old.
Fragmentary fossil remains of at least four humans thought to be intermediate between Homo erectus and archaic forms of The Homo sapiens, the later species to which all modern humans belong, were found in caves in Atapuerca in northern Spain, according to a report published in August. Dated as at least 780,000 years old by means of a Paleomagnetic dating technique, the stone tools and skeletal fragments - including some from an adolescent and some from a child - of skulls, hands, and feet represent the oldest humans yet discovered in Europe. The researchers who found the fossils said they could possibly be distant ancestors of the Neanderthals who appeared in Europe hundreds of thousands of years later.
The Spanish fossils partly fill a gap in the history of human evolution and expansion around the world. Previously, the oldest human fossils found in Europe, dating back 500,000 years, belonged to Heidelberg man, a likely ancestor of the Neanderthals, found at the Mauer site in Germany near the French border. It is known, however, that descendants of the earliest humans had spread from Africa to Asia well more than a million years ago. Among reasons given by anthropologists for the late occupation of Europe by Homo is the harshness of Europe's Ice Age climate.
Finds of Neanderthaloid skulls and skeletons continue to be reported from widely separated areas. Digging in a cave at Mount Circeo on the Tyrrhenian sea, 50 miles south of Rome, Italy, Alberto Carlo Blanc uncovered an almost perfectly preserved Neanderthal skull, perfect except for a fracture in the right temporal region. It is the third of this type found in Italy. The two skulls previously reported were found in 1929 and 1935 in the Sacopastore region, near Rome, but in not nearly so well preserved a condition as the present find. No other human bones were found here, but the skull was accompanied by fossilized bones of elephants, rhinoceri, and giant horses, all fractured, thus giving some evidence of the mode of life of Neanderthal man. Professor Sergio Sergi, of the Institute of Anthropology at the Royal University of Rome, who has studied this skull in detail believes it to be 70,000 to 80,000 years old. He concludes also that Neanderthal man walked almost as erect as modern man and not with head thrust forward as had hitherto been assumed.
Another Neanderthal skeleton is reported to have been found in a cave in Middle Asia by A. P. Okladnikoff of the Anthropological Institute of Moscow University and the Leningrad Institute of Anthropology. The bones of the skeleton were badly shattered, but the jaw and teeth of the skull, it crushed at the back, were almost complete
Hominids that were contemporary with Oldowan sites include two major lineages. One is the robust australopithecines (so called because their cheek teeth were larger than those of other australopithecines). These robust australopithecines - such as Australopithecus aethiopicus and Australopithecus boisei in East Africa, and Australopithecus robustus in South Africa - were bipedal and had small brains, large jaws, and large molars. The other lineage is made up of bipedal, larger-brained, and smaller-toothed early members of the genus Homo, such as an a Homo habilis, Homo rudolfensis, and early Homo erectus. The oldest fossils of A Homo erectus (sometimes called Homo ergaster) found in Africa dates back to about 1.85 million years ago. This species is characterized by an even larger brain and smaller teeth than earlier hominids and by a larger body size. (In 1984 anthropologists in Kenya found a nearly complete skeleton of an adolescent Homo erectus who would have been 1.8 m (6 ft) tall as an adult.)
Experts do not know for certain that of these species were responsible for individual Oldowan sites. These species may have made and used Oldowan-style stone tools to varying degrees. However, anthropologists have long suspected that the larger-brained and smaller-toothed Homo was probably a more habitual toolmaker. It is likely that Homo erectus was responsible for many Oldowan sites more recent than 1.85 million years ago. In any case, by one million years ago, all these species but The Homo erectus had gone extinct, so researchers can be certain that at least the Homo’s lineage was involved in using and making stone tools. The Homo erectus appears to have moved out of Africa and into Eurasia sometime before one million years ago, although some anthropologists think this geographic spread of hominids may have occurred nearly two million years ago. The everyday life of Oldowan hominids is largely a matter of archaeological conjecture. Most sites in East Africa are found near lakes or along streams, suggesting that they preferred to live near water sources. Studies of rock sources suggest that Oldowan hominids sometimes transported stone several kilometres to the sites where stone artifacts are found. Well-preserved sites often have collections of stone artifacts and fragmented fossil animal bones associated together, often in dense concentrations of several thousand specimens. Scholars disagree regarding the nature of these sites. Some archaeologists interpret them as camps, home bases, or central foraging places, similar to those formed by modern hunter-gatherers during their daily activities. Others think that such sites represent scavenging stations where hominids were primarily involved in processing and consuming animal carcasses. Still others view these accumulations as stone caches where hominids collected stone in areas where such raw materials did not occur naturally.
Fossil remains from some Oldowan sites suggest that Oldowan hominids used stone tools to process meat and marrow from animal carcasses, some weighing several hundred pounds. Although some archaeologists have argued that large game hunting may have occurred in the Oldowan, many Oldowan specialists believe these early Stone Age hominids likely obtained most of their meat from large animals primarily through scavenging. The early hominids may have hunted smaller animals opportunistically, however. Modern experiments have shown that sharp Oldowan flakes are especially useful for the processing of animal carcasses—for example, skinning, dismembering, and defleshing. The bulk of early hominid diet likely consisted of a variety of plant foods, such as berries, fruits, nuts, leaves, flowers, roots, and tubers, but there are little archaeological records of such perishable foodstuffs.
The term Acheulean was first used by 19th-century French archaeologist Gabriel de Mortillet to refer to remnants of a prehistoric industry found near the town of Saint-Acheul in northern France. The distinguishing feature of this site is an abundance of stone hand axes, tools more sophisticated than those found at Oldowan sites. The term Acheulean is now used to refer to hand axe industries in Africa, the Near East, Europe, and Asia dating from 1.5 million years ago to 200,000 years ago and spanning human evolution from A Homo erectus to early archaic Homo sapiens.
The characteristic Acheulean hand axe is a large, pointed or oval-shaped form. These hand axes were often made by striking a blank (a rough chunk of rock) from a larger stone and then shaping the blank by carefully removing flakes around its perimeter. Usually, both sides, or faces, of the blank were flaking, a process called bifacial flaking. Later Acheulean hand axes may have been produced by the soft-hammer technique, in which a softer hammer of stone, bone, or antler produced thinner, more carefully shaped forms. Other associated forms include cleavers, bifacial artifacts with a sharp, guillotine-like bit at one end; and thick, pointed artifacts known as picks. Simpler, typical Oldowan artifacts are usually also found at Acheulean sites, and a range of retouched flake tools such as scrapers. Experiments have demonstrated that Acheulean hand axes and cleavers are excellent tools for heavy-duty butchery activities, such as severing animal limbs. Some archaeologists, however, believe they may have served other functions, or perhaps were general, all-purpose tools.
Acheulean tools did not entirely replace Oldowan tools. Archaeologists have discovered numerous sites where Oldowan tools were used throughout the Acheulean time, sometimes in the same geographic region as Acheulean industries. Interestingly, the Acheulean might be especially restricted to Africa, Europe, and western Asia, with few sites in East Asia of stone industries with typical Acheulean hand axes and cleavers during the Lower Paleolithic. Most of the industries found in East Asia tend to be simpler, Oldowan-like technologies that can be seen at sites at Nihewan and the cave of Zhoukoudian in northern China.
Well-studied Acheulean sites include those at Olduvai Gorge and Isimila, in Tanzania; Olorgesailie, in Kenya; Konso Gardula and Melka Kunture, in Ethiopia; Kalambo Falls, in Zambia; Montagu Cave, in South Africa; Tabun and Gesher Benot Ya'aqov, in Israel; Abbeville and Saint-Acheul, in France; Swanscombe and Boxgrove, in England; and Torralba and Ambrona, in Spain.
Most anthropologists think that Acheulean populations of The Homo erectus and early Homo sapiens were probably more efficient hunters than Oldowan hominids. Recently discovered wooden spears from about 400,000 years ago at Schöningen, Germany, and a 300,000-year-old wooden spear tip from Clacton, England, suggest that the hominids who made these implements may have hunted game extensively.
Experts disagree about whether Acheulean hominids and their contemporaries harnessed the use of fire. Archaeologists have found evidence such as apparent burnt bone and stone, discoloured sediment, and the presence of charcoal or ash at most sites, including Cave of Hearths, in South Africa; Zhoukoudian, in China; and Terra Amata, in France. Discrete fireplaces (hearths), however, may be quite rare. Similarly, there is only questionable evidence of huts or other architectural features.
The Middle Paleolithic extends from around 200,000 years ago until about 30,000 years ago. It is also called the Mousterian Industry in Europe, the Near East, and North Africa and called the Middle Stone Age in sub-Saharan Africa.
Toolmakers in the Middle Paleolithic used a range of retouched flake tools, especially side-scrapers, serrated scrapers, backed knives (blade tools with the nonblade side dulled to fit comfortably in the hand), and points. Experts believe these tools were used to work animal hides, to shape wood implements, and as projectile points. This period is also characterized by specially prepared cores. Using the disc core method, a circular core could produce numerous flakes to serve as blanks for retouched tools. With the Levallois method (named after a suburb of Paris, France, where the first such artifacts were discovered), flakes of a predetermined shape were removed from specially prepared cores. This process resulted in oval-shaped flakes or large, triangular points, depending on the type of Levallois core. Levallois core and flakes are first seen at some late Acheulean sites but become much more common in the Middle Paleolithic/Middle Stone Age.
Some regional variation can be seen among Middle Paleolithic industries. A North African variant known as Aterian produced tools and point characterized by tangs (stems projecting from the base of the tool or point, to allow the tool to be attached to a handle or shaft). In Eastern Europe, a variant called Szeletian produced two-sided, leaf-shaped points, a style not usually seen elsewhere until the Upper Paleolithic. In Central Africa, a variant called the Sangoan produced a range of heavy-duty picks and axes.
Middle Paleolithic/Middle Stone Age archaeological sites are often found in the deposits of caves and rock shelters. Well-studied caves include Pech de l'Aze, Combe Grenal, La Ferrassie, La Quina, and Combe Capelle, in France; Tabun, Kebara, Qafzeh, and Skhul, in Israel; Shanidar, in Iraq; Haua Fteah, in Libya; and Klasies River Mouth, in South Africa. In East Asia, sites that are contemporary with the Middle Paleolithic often exhibit a simpler toolmaking technology, without as much standardization of the flake tool forms as in much of the rest of Eurasia and Africa.
Hominids associated with the Middle Paleolithic include Neanderthals and other archaic Homo sapiens (Homo sapiens predating anatomically modern humans, who lived from about 200,000 to 35,000 years ago). In Europe, the Middle Paleolithic is associated with Homo sapiens neanderthalensis, or Neanderthals, who lived from about 200,000 to 35,000 years ago. Neanderthals were short, robust humans with fully modern cranial capacity. They had more jutting faces, more prominent brow ridges, thicker cranial bones, and larger nose cavities than modern humans. Skeletal remains show that Neanderthals were very robust and muscular. Healed injuries to some skeletons suggest that Neanderthals led stressful, rigorous lives. Famous Neanderthal discoveries include Neander Valley, in Germany; La Chapelle-aux-Saints and La Ferrassie, in France; Krapina, in Croatia; Monte Circeo and Saccopastore, in Italy; Shanidar, in Iraq; and Tabun and Amud, in Israel. Fossils of an archaic Homo sapiens from this time have been found at sites such as Dali and Maba, in China and at Florisbad, in South Africa, and Ngaloba, in Tanzania. In addition, fossils interpreted as early anatomically modern humans have been found at some Middle Paleolithic/Middle Stone Age sites in parts of Africa and the Near East, such as at Qafzeh and Skhul, in Israel, and Klasies River Mouth, in South Africa.
Middle Paleolithic hominids appear to have been more successful hunters than their predecessors. Abundant animal remains suggest that these hominids ate many kinds of large mammals. It is unknown, however, how much of the meat consumed was obtained through hunting, as opposed to scavenging. Accumulations of remains at some sites show that some animals were of a common species and were adults in their prime, which some researchers suggest is an indication of efficient hunting behaviour. Several sites in Europe that contain the carcass of one or more large animals are believed to be butchery sites, where early humans processed the spoils of kills. Some archaeologists have also argued that some Middle Paleolithic stone points were probably attached to spears, a development in hunting technology. At Klasies River Mouth Cave in South Africa, archaeologists discovered a buffalo vertebra with a broken tip of what was probably a spearhead embedded in it, which could be evidence that the large mammal was hunted or trapped by hominids.
Middle Paleolithic hominids tend to show more behavioural complexity than their predecessors. For example, although most of the stone found at most Middle Paleolithic sites are local—its sources within a few kilometres of a site - an increasing percentage is exotic stone, transported from its sources tens of kilometres away. Simple hearths at many Middle Paleolithic sites suggest habitual fire use and possible firemaking as well. Evidence of housing is still quite uncommon, but is present at some sites. For example, at Molodovo, Ukraine, a circle of mammoth bones has been interpreted as a hut structure. Microscopic studies of residues on Middle Paleolithic scraper tools suggest that they may have been used for woodworking and to work animal hides for use as clothing or in shelters.
Over the Middle Paleolithic, hominids spread across much of Eurasia. The use of fire and clothing and the ability to build more substantial shelters may have helped them survive in cold regions, such as the central Asian steppe. By 40,000 years ago, near the end of the Middle Paleolithic, humans entered Australia, which apparently would have required traversing some distance of open ocean, probably in some form of craft. Some Middle Paleolithic sites have skeletal remains interpreted as simple burials. No representational art is known from this period, although occasional ornaments such as beads have been found at late Middle Paleolithic/Middle Stone Age sites.
Opinion is divided among anthropologists about whether Neanderthals and other archaic Homo sapiens had fully modern cognitive abilities, particularly the ability to recognize and communicate with symbols, a skill required to form modern languages. On one hand, the large cranial capacities of these populations might suggest modern human cognitive and behavioural capabilities. On the other hand, their technological development was very slow, and they left behind no trace of the use of symbols, such as representational cave paintings. Archaeologists have found much greater evidence of symbolism and cultural complexity during the Upper Paleolithic.
The Upper Paleolithic extends from approximately 40,000 years ago until the end of the last ice age, about 10,000 years ago. This era is known as the Paleo - Indian period in the Americas, and as the Later Stone Age in a sub - Saharan Africa, where it extended much longer, even to historical times in parts of the continent. In the Upper Paleolithic, standardized blade industries appear and become much more widespread than in previous times. The first of these industries to appear in the Near East and Europe is known as Aurignacian. Later Upper Paleolithic industries include the Perigordian, Solutrean, and Magdalenian. The Upper Paleolithic is usually characterized by specially prepared cores from which blades (flakes at least twice as long as they are wide) were struck off with a bone or antler punch. Upper Paleolithic humans also developed new forms of scrapers, backed knives, burins, and points. Beautifully made, two - sided, leaf - shaped points are also common in some Upper Paleolithic industries. Toward the end of the Upper Paleolithic, microliths (small, geometric - shaped blade segments) became increasingly common in many areas.
By the end of the Upper Paleolithic period and the end of the last ice age about 10,000 years ago, human populations had spread to every continent except Antarctica. Humans had effectively adapted to the northern latitudes of Eurasia and had dispersed into the American continents. The earliest well - documented occupation of the Americas appears to have been during the late ice age, about 12,000 to 10,000 years ago. The first recognized Paleo - Indian industry is known as Clovis, which was followed by Folsom. These industries produced delicately crafted, bifacial points fluted, meaning that the base of the point is thinned by removing a large flake from one or both sides. Fluted Clovis points have been found at mammoth kill sites, while Folsom points are associated with bison kills, mammoths being extinct by that time.
Famous Upper Paleolithic occupation sites include Laugerie Haute, La Madeleine, Abri Pataud, and Pincevent, in France; Castillo, Altamira, and El Juyo, in Spain; Dolní Vestonice, in the Czech Republic; Mezhirich, in Ukraine; Sungir and Kostenki, in Russia; Ksar Akil, in Lebanon; Kebara, in Israel; Zhoukoudian Upper Cave, in China; Haua Fteah, in Libya; and Taforalt, in Morocco. Well - known Later Stone Age sites in sub - Saharan Africa includes Lukenya Hill, in Kenya; Kalemba, in Zambia; and Rose Cottage Cave, Wilton Cave, Nelson Bay Cave, and Boomplaas in South Africa. The most famous Paleo - Indian sites are those moved to the United States near the eastern New Mexico towns of Clovis and Folsom, which gave the industries their names.
Human fossils associated with the Upper Paleolithic, Paleo - Indian, and Later Stone Age are usually those of anatomically modern humans, or The Homo sapiens. In the 19th century, Homo sapiens skeletal remains were found associated with early Upper Paleolithic artifacts at the rock shelter of Cro - Magnon in southern France. The term Cro - Magnon Man has thus sometimes been used to refer to anatomically modern humans from the Upper Paleolithic. Not all humans were anatomically modern in this period, however. In the early stages of the Upper Paleolithic, the sites that make up the Chatelperronian industry are associated with late Neanderthals, possibly influenced by modern humans arriving with Aurignacian technology.
During the Upper Paleolithic, tools of bone, antler, and ivory become common for the first time. These tools include points, barbed harpoons, spear throwers, awls, needles, and tools interpreted as spears - shaft straighteners. The presence of eyed needles indicates the use of sewn clothing (presumably of hide and possibly early textiles) or hide coverings for tents or shelters. In some carvings from this period, human figures are depicted wearing hooded parkas or other vestments. Other technological innovations include lamps (in hollowed out stones filled with flammable substances such as oil or animal fat) and probably the bow and arrow (small projectile points have been interpreted as arrowheads). Many Upper Paleolithic artifacts might be evidence of composite technology, in which multiple components were combined to form one tool or process. For example, spear tips were attached with binding material to spear shafts, which were flung using spear throwers (sometimes called atlatls). A spear thrower usually took the form of a length of wood or bone with a handle on one end and a peg or socket at the other to hold the butt of a spear or dart. When swung overhand together, the spear thrower provided greater thrust on the spear.
Upper Paleolithic populations appear to have been competent-hunter -gatherers. The use of mechanical devices such as spear throwers and, probably, arm bows and an arrowed weapon allowed them to increase the velocity, penetrating force, and distance of projectiles. Many Upper Paleolithic sites contain large quantities of mammal bones, often with one species predominating, such as red deer, reindeer, or horse. It is believed that many of these Upper Paleolithic hunter-gatherers could effectively predict the timing and location of seasonal resources, such as reindeer migrations or salmon runs.
Many Upper Paleolithic sites feature elements interpreted as evidence of housing. These are commonly patterns of bone or stone concentrations that seem to delineate hut or tent structures. At the sites of Étiolles and Pincevent, in France, the distribution of stone artifacts, animal bones, hearths, and postholes has been interpreted as evidence of clearly defined huts. At Mezhirich, in the Ukraine, and Kostenki, in Russia, hut structures were found made of stacked or aligned mammoth bones. Distinctive hearths, often lined or ringed with rocks, is much more common in the Upper Paleolithic than in earlier times.
Stone for tools was often obtained from more distant sources, sometimes in larger quantities than seen previously in the Stone Age. Occasionally, stone was traded or carried over several hundred kilometres. It seems likely, therefore, that trade and transport routes were more formalized than they had been in earlier times. The Upper Paleolithic also documents the trade of exotic materials - such as marine shells or semiprecious stones—for personal ornamentation as beads or on necklaces.
In the Upper Paleolithic, evidence of human burial is much more common. In addition, burials tend to be more elaborate than in Neanderthal times, often associated with rich grave goods. For example, at Sungir, in Russia, three individuals were buried with ivory spears, pendants and necklaces of shells and animal teeth, and thousands of ivory beads that had apparently been sewn into their clothing.
The earliest representational art—in the form of painting, sculpture, and engraving—dates back to approximately 32,000 years ago. Sites in Europe are famous for their artwork, but prehistoric Stone Age art has also been richly documented in Africa, Australia, and other parts of the world. Animals are common subjects of Upper Paleolithic art, and human figures and abstract elements such as lines, dots, chevrons, and other geometric designs are also found.
Early humans around the world used natural materials such as red and yellow ochre, manganese, and charcoal to create cave art. Among the hundreds of European sites with Upper Paleolithic cave paintings, some best known are Altamira, in Spain, and Lascaux and the more recently discovered (and archaeologically oldest) Chauvet, in France. Animals such as bison, wild cattle, horses, deer, mammoths, and woolly rhinoceroses are represented in European Upper Paleolithic cave art, with human figures relatively uncommon. Later Stone Age paintings of animals have been found at sites such as in Apollo 11 Cave, in Namibia; and stylized engravings and paintings of circles, animal tracks, and meandering patterns have been found in Australia’s Koonalda Cave and Early Man Shelter.
Many small sculptures of human female forms (often called Venus figurines) have been found in numerous sites in Europe and Asia. Small, stylized ivory animal figures made more than 30,000 years ago were discovered in Vogelherd, Germany, and clay sculptures of bison were found in Le Tuc d̀Audoubert, in the French Pyrenees. In addition, many utilitarian objects—such as spear throwers and batons—were superbly decorated with engravings, sculptures of animals, and other motifs.
The earliest known musical instruments also come from the Upper Paleolithic. Flutes made from long bones and whistles made from deer foot bones have been found at a number of sites. Some experts believe that Upper Paleolithic people may have used large bones or drums with skin heads as percussion instruments.
The archaeological record of the Upper Paleolithic shows a creative explosion of new technological, artistic, and symbolic innovations. There is little doubt that these populations were essentially modern in their biology and cognitive abilities and had fully developed language capabilities. There is a much greater degree of stylistic variation geographically (Some archaeologists have suggested that this be evidence of the emergence of ethnicity) and a more rapid developmental pace during the Upper Paleolithic than in any previous archaeological period. Anthropologists hotly debate whether these new Upper Paleolithic patterns are due to biological transition or whether they are simply the products of accumulated cultural knowledge and complexity through time.
The Mesolithic (also known as the Epipaleolithic) extends from the end of the Pleistocene Ice Age, about 10,000 years ago, until the period when farming became central to a peoples’ livelihood, which occurred at different times around the world. The term Mesolithic is generally applied to the period of post - Pleistocene hunting and gathering in Europe and, sometimes, parts of Africa and Asia. In the Americas, the post - glacial hunters - a gatherer stage that predates the dominance of agriculture is usually called the Archaic. In the rest of the world, Mesolithic sites are usually characterized by microliths. Microlithic blade segments were commonly retouched into a range of shapes, including crescents, triangles, rectangles, trapezoids, and rhomboids, and thus the tools are often called geometric microliths. These forms often have multiple sharp edges. Many of these microliths probably served as elements of composite tools, such as barbed or a knife edge - tipped spears or arrows, or wooden - handled knives. The microliths were likely inserted into shafts or handles of wood or antler and reinforced with some type of adhesive.
The end of the ice age brought rapid environmental change in much of the world. With the warmer, post - glacial conditions of the Holocene Epoch, ice sheets retreated and sea levels rose, inundating coastal areas worldwide. Temperate forests spread in many parts of Europe and Asia. As these climatic and vegetative changes occurred, large herds of mammals, such as reindeer, were replaced by more solitary animals, such as a red deer, roe deer, and wild pig. Cold - adapted animals, such as the reindeer, elk, and bison, retreated to the north, while others, such as the mammoth, giant deer, and woolly rhinoceros, went extinct. The rich artistic traditions of Upper Paleolithic Western Europe declined markedly after the end of the ice age. This may in part be because the changing environment made the availability of food and other resources less predictable, requiring populations to spend more time searching for resources, leaving less time to maintain the artistic traditions.
Well - studied Mesolithic/Archaic sites include Star Carr, in England; Mount Sandel, in Ireland; Skara Brae, in Britain’s Orkney Islands; Vedbæk, in Denmark; Lepenski Vir, in Serbia; Jericho, in the West Bank; Nittano, in Japan; Carrier Mills, in Illinois; and Gatecliff Rockshelter, in Nevada. In the sub - Saharan Africa, many Later Stone Age sites of the Holocene Epoch could broadly be termed Mesolithic, due to their geometric microliths and bow and arrow technology.
During the Mesolithic, human populations in many areas began to exploit a much wider range of foodstuffs, a pattern of exploitation known as broad spectrum economy. Intensively exploited foods included wild cereals, seeds and nuts, fruits, small game, fish, shellfish, aquatic mammals and birds, tortoises, and invertebrates such as snails. Dogs were domesticated in this period, probably for use in hunting. Some Mesolithic hunter-gatherers, such as the Natufian of the Near East, appear to have lived in small settlements based on an economy involving gazelle hunting and the harvesting of wild cereals using sickles with flint blade segments inset in bone handles. In the Near East and North Africa, Mesolithic populations processed wild plant foods using grinding stones.
Other Mesolithic technological innovations include the adz and axe (woodworking tools consisting of flaked stone blades set in bored antler sleeves and fastened to wooden handles), fishing weirs and traps, fishhooks, the first preserved bows and arrows, baskets, textiles, sickles, dugout canoes and paddles, sledges, and early skis. The Jomon culture of Japan produced pottery by 10,000 years ago, as did the Ertebølle culture of Scandinavia moderately later.
The development of broad spectrum economies in the post - glacial Mesolithic/Archaic period laid the foundations for the domestication of plants and animals, which in turn led to the rise of farming communities in some parts of the world. This development marked the beginning of the Neolithic.
Farming originated at different times in different places—as early as about 9,000 years ago in some parts of the world. In some regions, farming arose through indigenous developments, and in others it spread from other areas. Most archaeologists believe that the development of farming in the Neolithic was one of the most important and revolutionary innovations in the history of the human species. It allowed more permanent settlements, much larger and denser populations, the accumulation of surpluses and wealth, the development of more profound status and rank differences within populations, and the rise of specialized crafts.
Neolithic Toolmaking generally shows an advanced portion of technological continuity with the Mesolithic, however, Neolithic industries often include blade and bladelet (small blades) technologies, and sometimes in the accompaniment with microliths. A vast horizon widened by a range-over of retouched tools, including endscrapers (narrower scrapers for working hides). Moreover, be in the back blades or bladelets (some of which were set into handles and used as sickles), and a widen range of activated points. In addition, ground and polished axes and adzes—which would have been used for forest clearance to plant crops, and for woodworking activities—are characteristic of the Neolithic. Such tools, although labour - intensive to manufacture, has a tendency to last a long time without requiring resharpening and consequently were highly prized by these early farmers. Large - scale trade networks of axes and stone are documented in the Neolithic, with artifacts sometimes found hundreds of miles from their sources. Other technological developments in the Neolithic include grinding stones, such as mortars and pestles, for the processing of cereal foods, the widespread use of pottery for surplus food storage and cooking, the construction of granaries for storage of grains, the use of domesticated plant fibres for textiles, and weaving technology.
Archaeologists have several theories to explain why humans began farming. The reasons probably differed moderately from one region to another. Some theories maintain that population pressure or changes in environment may have forced humans to find new economic strategies, which led to farming. Another theory maintains that a population of humans may have lived in a region where domesticating wild plants and animals was relatively easy, making the development of agriculture essentially a historical accident. Still another theory proposes that the rise of farming may have varied with social change, as individuals began to use agriculture as a means to acquire wealth as food surpluses.
Different plant crops were cultivated in different places, depending on what wild plants grew naturally and how well they responded to cultivation. In the Near East, important crops included wheat, barley, rye, legumes, walnuts, pistachios, grapes, and olives. In China, millet and rice predominated. In Africa, millet, sorghum, African rice, and yams were commonly grown. Rice, plantains, bananas, coconuts, and yams were important in Southeast Asia. Finally, in the Americas, corn, squash, beans, potatoes, peppers, sunflowers, amaranths, and goose - foots were commonly grown.
Domesticated animals also varied from one region to another according, again, to availability and their potential to be domesticated. In Eurasia, Neolithic people domesticated dogs, sheep, goats, cattle, pigs, chickens, ducks, and water buffalo. In the Americas, domesticated animals included dogs, turkeys, llamas, alpacas, and guinea pigs. In Africa, the primary domesticated animals - cattle, sheep, and goats - probably spread from the Near East.
Well - studied early farming sites in Eurasia include Jericho, in the West Bank; Ain Ghazal, in Jordan; Ali Kosh, in Iran; Mehrgarh, in Pakistan; Banpocun (Pan - p’o - ts’un), in China; and Spirit Cave, in Thailand. Important African sites include Adrar Bous in Niger, Iwo Eleru in Nigeria, and Hyrax Hill and Lukenya Hill in Kenya. In the Americas, sites showing early plant domestication include Guila Naquitz, in Mexico, and Guitarrero Cave, in Peru.
Larger Neolithic settlements show a variety of new architectural developments. For instance, in the Near East, conical beehive - shaped houses or rambling, connected apartments - style housing was often constructed with mud bricks. In Eastern Europe, houses were made with wattle and daub (interwoven twigs plastered with clay) walls, and, in later times, longhouses were constructed with massive timbers. In China, some settlements contain semisubterranean houses dug into clay, with evidence of walls and roofs made out of thatch or other materials and supported by poles.
The domestication of plants and animals led to profound social change during the Neolithic. Surpluses of food, such as stored grain or herds of livestock, could become commodities of wealth for some individuals, leading to social differentiation within farming communities. Trade of raw materials and manufactured products between different areas increased markedly during the Neolithic, and many foreign or exotic goods appear to have developed special symbolic value or status. Some Neolithic graves contain rich stores of goods or exotic materials, revealing differentiations in terms of wealth, rank, or power
In certain areas, notably parts of the Near East and Western Europe, Neolithic peoples erected massive ceremonial complexes, efforts that would have required extensive, dedicated work forces. Large earthworks and megalithic (“giant stone”) monuments from the Neolithic (including the Avebury stone circle and the earliest stages of Stonehenge, in England, and the monuments of Carnac, in France), suggest more highly organized political structures and more complex social organization than among most hunters - gatherer populations. In the Americas, sites such as the mounds of Cahokia, in Illinois, also indicate a more complex, organized political and social order. The technological innovations and economic basis established and spread by Neolithic communities ultimately set the stage for the development of complex societies and civilizations around the world.
Humans produced metal tools and ornaments from beaten copper as early as 12,000 years ago in some parts of the world. By 6,000 years ago, early experiments in metallurgy, particularly extracting metals from copper ore (smelting), were being conducted in some parts of Eurasia, notably in Eastern Europe and the Near East. By 5,000 years ago, copper and tin ores were being smelted and alloyed in some regions, marking the dawn of the Bronze Age. Casting of bronze tools - such as axes, knives, swords, spearheads, and arrowheads - became increasingly common over time. At first, copper and bronze tools were rare and stone tools were still very common, but as time went on, metal tools gradually replaced stone as the principal raw material for edged tools and weapons.
In Eurasia and parts of Africa, the rise of metallurgical societies appears to coincide with the rise of the earliest state societies and civilizations, such as ancient Egypt, Sumer, Minoan Culture, Mycenae, and China. In the Americas, parts of sub-Saharan Africa, Australia, and the Pacific Islands, societies continued to use stone and other nonmetal materials as the principal raw materials for tools up to the time of European contact, starting in the 15th century ad. Although, technically, populations in these areas could have been said to be Stone Age groups, many had become agricultural societies and had formed flourishing civilizations.
Stone technology enjoyed a brief resurgence within iron-using societies with the advent of flintlock firearms, beginning in the 17th century. Carefully shaped flints—reminiscent of the geometric microliths of the Mesolithic and early Neolithic-were struck against steel to create a spark to ignite the firearm. By the end of the 20th century few human groups had a traditional stone technology, although a few groups on the island of New Guinea still relied on the use of stone adzes. Tools of metal, plastic, and other materials had replaced stone technologies virtually everywhere.
Cave Dwellers, is the term used to designate an ancient people who occupied caves in various parts of the world. Cave dwellers’ date generally from the Stone Age period known as the Paleolithic, which began as early as 2.5 million years ago. Caves are natural shelters, offering shade and protection from wind, rain, and snow. As archaeological sites, caves are easy to locate and often provide conditions that encourage the preservation of normally perishable materials, such as bone. As a result, the archaeological exploration of caves has contributed significantly to the reconstruction of the human past.
Cave Painting, of Lascaux, France where some Palaeolithic artists painted scenes in caves more than 15,000 years ago, such as the one here found in Lascaux, France. The leaping cow and group of small horses were painted with red and yellow ochre that were either blown through reeds onto the wall or mixed with animal fat and applied with reeds or thistles. It is believed that prehistoric hunters made these paintings to gain magical powers that would ensure a successful hunt.
Wherever caves were available, prehistoric nomadic hunters and gatherers incorporated them into the yearly cycle of seasonal camps. Most of their activities took place around campfires at the cave mouth, and some caves contain stone walls and pavements providing additional protection from winds and dampness. Hunting, particularly of reindeer, horse, red deer, and bison, was important; many caves are situated on valley slopes providing views of animal migration routes.
Stone Toolmaking Humans first made tools of stone at least 2.5 million years ago, initiating the so-called Stone Age. The Stone Age advanced through three stages over time - the Paleolithic (which is subdivided into Lower, Middle, and Upper periods), Mesolithic, and Neolithic. Blade toolmaking, as demonstrated in this video, was a development of the Upper Paleolithic, which began about 40,000 years ago. This technique produced a far greater variety and higher quality of tools than did earlier methods of toolmaking.
Artifacts have been found in caves in France, Spain, Belgium, Germany, Italy, and Great Britain. The association of these remains with the bones of extinct animals, such as the cave bear and saber-toothed tiger, indicates the great antiquity of many cave deposits. A variety of stone and bone points discovered in excavated caves documents the importance of spears until the bow and arrow appeared in the late Paleolithic era. Other common tools included stone scrapers for working hides and wood, burins for engraving, and knives for butchering and cutting. Throughout the Paleolithic period such tools became increasingly diverse and well made. Bone needles, barbed harpoons, and spear-throwers were made and decorated with carved designs. Evidence of bone pendants and shell necklaces also exists. Among the caves that have yielded relics of early humans are the Cro-Magnon and Vallonnet in France.
Wall paintings and engravings have been found in more than 200 caves, largely in Spain and France, dating from 25,000 to 10,000 years ago. Frequently found deep inside the caves, and the paintings depict animals, geometric signs, and occasional human figures. In the cave of La Colombière in France, a remarkable series of sketches engraved on bone and smoothed stones was unearthed in 1913. In caves such as Altamira in Spain and Lascaux in France, multicolored animal figures were drawn using mineral pigments mixed with animal fats. Some paintings adorn walls of large chambers suitable for ritual gatherings; others are found in narrow passages accessible only to individuals. Hunting and fertility seems to have been important artistic themes. The ritual gatherings themselves promoted communication and intermarriage among the normally scattered small groups. Chinese caves contain some earliest evidence of human use of fire
On every continent, prehistoric foragers used caves. In the Zhoukoudian (Chou-k'ou-tien) Cave near Beijing, China, remains of bones and tools of A Homo erectus (Peking Man) have been discovered. Chinese caves contain some earliest evidence of human use of fire, approximately 400,000 years ago. In the Shânîdâr Cave in Iraq, 50,000-year-old Neanderthal skeletons were unearthed in 1957. Ancient pollen buried with them has been interpreted as evidence that these cave dwellers had developed funeral rituals. In the western deserts of North America, caves have been located that contain plant foods, woven sandals, and baskets, representing the desert culture of a belated 9000 years ago. Early inhabitants of Australia, the Middle East, and the Peruvian Andes have also left remains in caves.
Gradually people learned to grow food, rather than forage for it. This was the beginning of the Neolithic age, which, although ending in western Europe some 4500 years ago, continued elsewhere in the world until modern times. Once agriculture became important, people established villages of permanent houses and found new uses for caves, mainly as hunting and herding campsites and for ceremonial activities. In Europe, Asia, and Africa caves continued to be used as shelters by nomadic groups.
Cave Dwellings These cave dwellings are located in the Cappadocia region of Central Anatolia Göreme, Turkey. Known as ”fairy chimneys,“ they were carved into soft volcanic rock by anchorite (hermitic) Christian monks in the 4th century AD. Many of these dwellings are still occupied by Göreme Turks, who consider them to be healthy and inexpensive places to live Arcaid/Nick Meers
In dry caves, preservation is often excellent, due to moistureless air and limited bacterial activity. Organic remains such as charred wood, nutshells, plant fibres, and bones are sometimes found intact. In wet caves, artifacts and other remains are often found encrusted with, or buried beneath, calcareous deposits of dripstone. The collected evidence of human habitation on the cave floor was often buried under rockfalls from the ceilings of caverns. Intentional burials have also been found in several cave sites.
Because of the unusual preservative nature of caves and the great age of many remains found in them, the fallacious belief has arisen that a race of cave people existed. Most cave sites represent small, seasonal camps. Because prehistoric people spend a copious measurement of the year in open-air camps, the caves contain the remains of only part of a group’s total activities. Also, the cultural remains outside caves were subject to greater decay. Thus, the archaeological record of remote times is better seen in cave deposits.
Caves have been systematically excavated during the past one hundred years. Since they often contain the remains of repeated occupations, caves can document changing cultures. For example, the economic transition from food collecting to agriculture is demonstrated by finds in highland Mexico and in Southeast Asia. Some caves in the Old World continued to be inhabited even after the close of the Stone Age; relics from the Bronze and Iron ages have been found in cave deposits. On occasion, material dating from the time of the Roman Empire has been recovered. The famous Dead Sea Scrolls, discovered in 1947, were preserved in caves.
In 1935 Doctor F. Kohl-Larsen discovered fragments of two skulls in the gravels at the northeast end of Lake Eyassi, Tanganyika Territory, Africa, in association with fossilized bones of antelopes, pigs, and hyenas resembling types of animals now living in that area. The two hundred fragments of the skulls have been painstakingly assembled by Doctor Hans Weinert of Kiel, Germany, so that there are now available for study the skull cap of one individual and part of the face of another. Though critical study of these East African finds is still far from completion, their closest resemblance may be to Pithecanthropus erectus, the famous Java ape man. These remains have been tentatively dated as 100,000 years ago.
Doctor Robert Broom of the Transvaal Museum, Pretoria, has continued his study of the human-like ape remains found in South Africa. He believes the Australopithecus skulls to be the most definitely ape-like, except their teeth, which show a closer similarity to those of man than of the gorilla or chimpanzee, and therefore that they are not actual ancestors of man, but rather, survivors of a possible ape-like ancestral stock that existed before Ice Age times.
The distal end of a humerus, the proximal ends of an ulna, and the distal phalanx of a toe of Paranthropus robustus, and the distal ends of a femur of Plesianthropus were excavated in the Pleistocene bone breccia of Kromdrai, near Krugersdorp, South Africa, under the direction of Doctor Broom, thus suggesting that this early type of ape-man walked erect, and making a distinct departure from previous assumptions as to posture of this species.
Professor Raymond Dart of Witwatersrand University (South Africa), the discoverer of the controversial Taungs skull (Australopithecus africanus) states that a high culture existed in the present habitat of the Bantu-speaking peoples of South Africa in the Late Stone Age before their advent in that part of Africa. Skeletons associated with the Mapungobwa finds appear to indicate that the civilization cantering to this place was associated with a race said to be intermediate between, and possibly a hybrid of, Cro-Magnon and Neanderthal types, which as known in Europe, are distinct races
Finds of Neanderthaloid skulls and skeletons continue to be reported from widely separated areas. Digging in a cave at Mount Circeo on the Tyrrhenian sea, 50 miles south of Rome, Italy, Alberto Carlo Blanc uncovered an almost perfectly preserved Neanderthal skull, perfect except a fracture in the right temporal region. It is the third of this type found in Italy. The two skulls previously reported were found in 1929 and 1935 in the Sacopastore region, near Rome, but in not nearly so well preserved a condition as the present find. No other human bones were found here, but the skull was accompanied by fossilized bones of elephants, rhinoceri, and giant horses, all fractured, thus giving some evidence of the mode of life of Neanderthal man. Professor Sergio Sergi, of the Institute of Anthropology at the Royal University of Rome, who has studied this skull in detail believes it to be 70,000 to 80,000 years old. He concludes also that Neanderthal man walked almost as erect as modern man and not with head thrust forward as had hitherto been assumed.
Another Neanderthal skeleton is reported to have been found in a cave in Middle Asia by A. P. Okladnikoff of the Anthropological Institute of Moscow University and the Leningrad Institute of Anthropology. The bones of the skeleton were badly shattered, but the jaw and teeth of the skull, such as for themselves were crushed at the back, were almost complete.
The famous Chokoutien site near Peking, China, the home of ancient Peking man (Sinanthropus) previously reported, now proves also to have yielded additional more modern type skeletons studied by Doctor Franz Weidenreich and Doctor W. C. Pei, the leaders in research at this site. In the portion of the site known as the upper cave were found the remains of a relatively advanced culture suggesting a resemblance to the Late or Upper Paleolithic in Europe, thus implying an age of 100,000 to 200,000 years. These cultural remains were accompanied by skeletons of bear, hyena, and ostrich, long extinct forms, and tiger and leopard that longs since disappeared from this part of Asia. The three human skulls in condition good enough for detailed study indicate that they probably belong to three different racial groups. Of the two female skulls studied, one bears close resemblance to the skulls of modern Melanesians, with frontal deformation; the second to Eskimo skulls. The brain case of the male skull is in some respects very primitive, almost in the Neanderthaloid stage, but in other features is reminiscent of Upper Paleolithic Man. The face, is similar to, though not identical with, recent Mongolians. From this evidence it seems that racial mixture is no product of modern times, but has its roots in extreme antiquity. It should be noted also that though Mongolian types resembling the modern population of North China were not found in the upper cave, it does not necessarily mean that they were nonexistent during that period. It has been suggested that the population represented in the upper cave may have been a migrating group. Historic and prehistoric American Indian skulls resembling Melanesian, Eskimo, or more primitive types have been reported from time to time in America, so that it would appear from the present finds at Chokoutien that long before migrations from Asia to America are assumed to have taken place, types similar to those composing the native American populations were living permanently, or at least moving around in Eastern Asia
In America, the search for additional evidence of Folsom Man continues. Near Fort Collins, Colorado, Doctor Frank H. H. Roberts, Jr., continued excavation at a camp site, uncovering a variety of tools and weapons, and the first known decorated objects from any Folsom site, two decorated beads. This earliest American. Folsom Man, may have lived contemporaneously with Old World Cro-Magnon Man, or some 25,000 years ago. This tentative date was assigned recently by Doctors Kirk Bryan and Louis L. Ray of Harvard University based on studies made at the Folsom camp site, known as the Lindenmeier site, in northeastern Colorado. Many stone points, identified as typically Folsom were found in an earth stratum above the floor of an ancient valley that is traceable to a terrace on a local stream. The terrace has been dated as of the late Ice Age. The dating is based on the assumed correlation between this late Ice Age stage with the Mankato of the Middle West and the Pomeranian of Europe. From this it appears that the culture-bearing layer of the Lindenmeier site was developed at the end of the glacial advance, or 25,000 years ago.
An attempt has been made to adapt the method of dating ruins by analysis of tree rings, so successfully carried out in America, specifically in Southwestern United States, to Viking ruins in Southern Norway. E. de Geer, who has been carrying on this work, reports, that, from a study of the remaining timbers in a wooden burial chamber in a Viking mound, it was constructed in 931 ad. A Swedish fort in Gotland was found by the same method to have been built in five Ad.
The Homo habilis, is an extinct primate classified in the subfamily Homininae, a group that includes humans. Scientists believe this species lived in Africa between two million and 1.5 million years ago. H. habilis are the earliest known member of the genus Homo, the branch of Hominines believed to have evolved into modern humans. The term Homo habilis means handy man, a name selected for the deposits of primitive tools found near H. habilis see fossils.
Scientists distinguish H. habilis from australopithecines, the more primitive Hominines from which it evolved, by analysing key physical characteristics. H. habilis had a larger brain than australopithecines. The braincase of H. habilis measured at least 600 cubic centimetres
(37 cu inches) compared with the 500 cu cm (31 cu in) typical of australopithecines. Australopithecines had long arms and short legs, similar to the limbs of apes. The overall body form of australopithecines was also apelike in having large body bulk relative to its height. Proportionally, H. habilis resembled modern humans with its limbs and small body bulk relative to its height. H. habilis had smaller cheek teeth (molars) and a less protruding face than earlier Hominines. H. habilis were taller than australopithecines, but shorter than Homo erectus, a later, more humanlike species.
The use of primitive tools implies that H. habilis had developed a different way of gathering food than earlier Hominines, which fed only on vegetation. H. habilis probably ate meat plus fruits and vegetables. Anthropologists disagree on whether H.habilis obtained this meat through hunting, scavenging, or a combination of both techniques
British-Kenyan anthropologist Louis Leakey discovered the first fossil evidence of H. habilis at Olduvai Gorge in northern Tanzania in 1960. Other anthropologists have since discovered specimens in northern Kenya, South Africa, and Malawi. Although all these specimens had a larger brain than australopithecines, some had especially large brains (almost 800 cu cm or 49 cu in) and more modern skeletons. However, their large and slightly protruding faces seem more primitive than those of other H. habilis specimens. Most scientists now believe that these fossils represent a distinct species named Homo rudolfensis. Scientists debate over which of these two species evolved into the later, even larger-brained H. erectus. Many consider H.rudolfensis the more likely candidate because of its large brain and more modern skeleton. For anthropology, the science of man, 1964 was an eventful and exciting year. Perhaps the most important development of 1964 was the discovery in Africa of a new humanlike, tool-using species, possibly a direct ancestor of man. This was not the only remarkable thing. The new species, named Homo habilis, was very old, probably 1.75 million years old, which makes him nearly twice as old as any previously known tool-using animal. The appearance of Homo habilis on the scene caused great excitement between paleontologists and physical anthropologists and has led many of them to a major reconsideration of much of man's biological history
The new discovery, like so many other important finds of recent years, was made by the top fossil finder of the 20th century, Louis S. B. Leakey, curator of the Coryndon Museum Centre for Prehistory and Paleontology, Nairobi, Kenya. Professor Leakey's work is invariably done with his wife. Mary, a geologist, and their three sons, who have also recovered important fossil materials. The finds were made in the incredibly fossil-rich Olduvai Gorge, an arid chasm in the Serengeti Desert of mainland Tanzania (formerly Tanganyika). The section of Olduvai Gorge excavated by the Leakeys is the most spectacular single prehistoric site in the world. The gorge cuts directly through four main stratigraphic levels, or beds, and in these four beds there are undisturbed paleontological and archaeological deposits covering a time span of nearly two million years. The gorge contains the stratified records of the development of stone tools from the most simple beginnings to elaborately fashioned hand axes; it contains fossil evidence of four major types of men or near-men; and it is rich in fossil remains of ancient fauna, including insects, fish, reptiles, birds, and mammals of the lower and middle Pleistocene periods.
The Homo habilis excavations were announced by Dr. Leakey at the National Geographic Society in Washington, D.C., and in the Apr. 4, 1964, issue of Nature. The Olduvai fossil remains are being studied by Professor Phillip Tobias, University of Witwatersrand, Johannesburg, and Dr. John R. Napier, Royal Free Hospital School of Medicine, London.
The Leakeys found bones and teeth representing 16 hominid individuals in beds’ I and II (the two lowest beds) of Olduvai Gorge. One of these was the well-known Zinjanthropus, which is placed roughly in the genus Australopithecus. The australopithecines were a genus of near-men living about one million years ago, perhaps a little earlier. They were originally considered close to the direct line of man's ancestry, but this is now in doubt. All of the other finds are considered by Leakey, Tobias, and Napier to represent Homo habilis, a more advanced hominid with a size and shape intermediate between Australopithecus and Homo, the genus that includes modern man and his immediate ancestors of the past 500,000 years. The specific name habilis are from the Latin and means "able, handy, mentally skillful, vigorous."
Not all of the 206 bones making a complete skeleton of Homo habilis have yet been discovered. The recovered parts, however, are numerous enough to give a good picture of his anatomy and, by inference, of his behaviour. The recovered parts include the remains of two or three skulls, three mandibles (jawbones), about 40 teeth, parts of a hand and foot, the bones of a lower leg, a collarbone, and some rib fragments.
Some features distinguishing modern man from his ancestors of earlier epochs include legs and feet adapted for upright posture and bipedal gait; hands adapted for tool use rather than locomotion; teeth and jaws adapted for an omnivorous rather than a purely herbivorous diet; a brain adapted for good hand-eye coordination in tool manufacture and use; and the ability to communicate with language of the human sort. Except language, the foot, hands, jaws, teeth, and brain case of Homo habilis indicate his close relatives crossed the line between the prehumans and human grades.
The fossil foot is nearly complete, lacking only the back part of the heel and the toes. The foot bones are within the range of variation of Homo sapiens. The large toe is stout and carried parallel to the other toes; the longitudinal and transverse arch system is like ours. The bones of the foot and leg show the adult Homo habilis had an upright posture and bipedal locomotion, a slender body build, and a stature of about four feet.
The hands are not entirely apelike, nor are they typically human. The hand bones are heavier than ours, and the finger bones are curved inward. The tips of the fingers and thumb are broad, stout, and covered by flat nails, as our modern man's. Probably Homo habilis could not oppose his thumb and fingertips in the precision, pen-holding grip of modern man, but his hand can make stone tools.
The jaws are smaller than those of Australopithecus; the front of the lower jaw is retreating, with no development of an external bony chin. The incisor teeth are relatively large, the canines are large relative to the premolars, and the premolars and molars are narrow in the tongue-to-cheek dimension. Both the manlike proportions of the teeth and the remains of fish, reptiles, birds, and small mammals found in his living sites show that Homo habilis had an omnivorous diet.
The skull is intermediate in shape between Australopithecus and modern man. The mass of the facial relative to the cranial part of the skull is reduced and is thus more like the advanced forms. The greatest breadth of the skull is high on the vault. The curvature of the parietal bones is intermediate; that of the occipital bone resembles Homo sapiens.
The brain case of the Olduvai specimen known as No. 7 has an estimated endocranial volume of 680 cc. The endocranial volume for australopithecines ranges from 435 to 600 cc., that of pithecanthropines from 775 to 1,225 cc., and that of modern man from about 1,000 to 2,000 cc., with an average of about 1,350 cc. Thus, the brain of Homo habilis, although both absolutely and relatively larger than any of the australopithecines, were not large, either absolutely or relatively, contrasted with that of modern man. A typical adult Homo habilis had a body weight of about 75 pounds and a brain weight of a little more than one pound, whereas a modern man of 150 pounds has a brain weight of about 3 pounds. In the period following Homo habilis, hominid body weight doubled, but the weight of the brain tripled.
The stone tools found in association with Homo habilis are typical of the Oldowan industry first recognized by Leakey 30 years ago. Similar tools are found elsewhere in East Africa, and in South Africa, Angola, and North Africa. These tools are commonly called pebble tools because most of them are made from waterworn pebbles. Most of the Oldowan choppers are worked on both faces to produce a sharp but irregular cutting edge.
These rough choppers made from potato-sized pieces of stone are the earliest known stone tools; they date from the very beginning of the Pleistocene. There is abundant evidence from Olduvai Gorge showing that the great hand ax or Chelles-Acheul culture evolved directly from the Oldowan stone industry.
Oldowan pebble tools and the skeletal remains of Homo habilis are associated in six sites. At some East and South African sites, pebble tools are also found in association with Australopithecus, but Homo habilis are, according to Professor Tobias, always associated with Oldowan tools, whereas Australopithecus is not. The evidence from the six sites certainly shows that early hominids regularly manufactured tools of a set design before they developed hands or brains like those of modern man.
The age of Homo habilis is as new and unexpected as the fossils themselves. Before these new finds most anthropologists thought the earliest toolmakers lived less than one million years ago. The potassium-argon process of dating had more than doubled the age of known tool manufacture.
The principle of the potassium-argon technique is simple. The radioactive isotope potassium 40 (K40) found in volcanic rock is known to disintegrate into calcium 40 and argon 40 (A40), an inert gas. The rate of transmutation is constant and very slow; one half the K40 atom changes to A40 atoms each 1.3 billion years. The phosphorus-containing mineral anorthoclase is found in the volcanic deposits of Olduvai Gorge. While the lava was in a molten state beneath the earth, no A40 accumulated in the mineral because the gas boiled away. After the lava erupted and cooled, however, nearly all newly formed A40 atoms were imprisoned in the crystalline structure of the anorthoclase. By removing the mineral at a low temperature and then heating it, scientists have succeeded in collecting the released A40 atoms to be counted in a mass spectrometer. Because no A40 was initially present and because the rate of accumulation is also known, this count gives an estimate of the age of the rock. Several samples give age estimates ranging from 1.57 to 1.89 million years, or an average of 1.75 for Bed I in Olduvai, where Homo habilis were found and where the first tools of hominid manufacture appear.
Homo erectus is an extinct primate classified in the subfamily Homininae and the genus Homo, which include humans. Scientists learn about extinct species, such as Homo erectus, by studying fossils—petrified bones buried in sedimentary rock. Based on their analysis of these fossils, scientists believe that Homo erectus lived from about 1.8 million to 30,000 years ago. Until recently, Homo erectus was considered an evolutionary ancestor of modern humans, or Homo sapiens.
The anatomical features of Homo erectus are more humanlike than those of earlier Hominines, such as australopithecines and Homo habilis. Homo erectus had a larger brain, measuring up to 1150 cc, and a rounder cranium - the portion of the skull that covers the brain - than earlier Hominines. Homo erectus was also taller, with a flatter face and smaller teeth. Large differences in body size between males and females, characteristic of earlier hominine species, are less evident in Homo erectus specimens.
This larger brain and more modern body-enabled Homo erectus to do many things its hominine ancestors had never done. Homo erectus appears to have been the first hominine to venture beyond Africa. It was the first hominine capable of systematic hunting, the first to make anything resemble home bases (campsites), and the first to use fire. Evidence suggests that the childhood of Homo erectus was longer than that of earlier Hominines, providing an extended period in which to learn complex skills. These skills are reflected in the relatively sophisticated stone tools associated with Homo erectus fossils. Although still primitive compared with the tools made by early Homo sapiens, the tools made by Homo erectus are much more complex than the simple, small pebble tools of earlier Hominines. The most characteristic of these tools was a teardrop-shaped hand ax, known to archaeologists as an Acheulean ax.
Scientific study of Homo erectus began in the late 19th century. Excited by Charles Darwin‘s theory of evolution and fossil discoveries in Europe, scientists began to search for the fossilized remains of “the unknown factor,” the evolutionary ancestor of both human beings and modern apes. In 1891 Dutch anthropologist Eugene Dubois travelled to Java, Indonesia, where he unearthed the top of a skull and a leg bone of an extinct hominine. Measurements of the skull indicated that the creature had possessed a large brain, measuring 850 cc, while the leg-bone anatomy suggested that it had walked upright. In recognition of these characteristics, Dubois named the species Pithecanthropus erectus, or “erect ape-man.”
Canadian anthropologist Davidson Black found similar fossils in China in the late 1920s. Black named his discovery Sinanthropus pekinensis, or “Peking Man.” Later studies by Dutch scientist G. H. von Koenigswald and German scientist Franz Weidenreich showed that the fossils discovered by Dubois and Black came from the same species, which was eventually named Homo erectus.
Since these earliest discoveries, Homo erectus fossils have been found in East Africa, South Africa, Ethiopia, and various parts of Asia. Kenyan fossil hunter Kamoya Kimeu discovered an almost complete Homo erectus skeleton, known as the Turkana boy, near Lake Turkana in northern Kenya in 1984. The oldest known specimen, dated at almost two million years old, also comes from northern Kenya. Recently developed dating methods have shown that Homo erectus also lived in Java almost two million years ago
Scientific assumptions about Homo erectus have changed dramatically since the early 1990s. Anthropologists long assumed that the species spread from Africa to parts of Asia and Europe and that these dispersed populations gradually evolved into Homo sapiens, or modern humans. Most anthropologists now think it more likely that Homo sapiens originated from a small population in Africa within the past 200,000 years. According to this theory, descendants of this African population of Homo sapiens spread throughout the eastern hemisphere, replacing populations of more ancient Hominines, perhaps with limited interbreeding.
Many anthropologists now believe that some Homo erectus specimens should be classified as a separate species named Homo ergaster. According to this view, Homo ergaster appeared first in East Africa and quickly spread into Asia, where it evolved into Homo erectus. Homo sapiens arose in Africa from a population descended from Homo ergaster. Until recently, Homo erectus was thought to have died out about 300,000 years ago. Recent studies of Homo erectus populations in Java suggest that they may have lived until as recently as 30,000 years ago, long after the evolution of modern humans.
Anthropologists also debate whether Homo erectus used language. Some scientists argue that the brain size of Homo erectus, the shape of its vocal structures, and the complexity of its behaviour indicate that it had a capacity for spoken language far beyond the rudimentary vocalizations of apes. Other anthropologists reject this conclusion. They point out that the first evidence of artistic expression, a trait closely linked with language, appears only about 40,000 years ago. These skeptics also point to the primitive quality of the tools associated with Homo erectus. Some anatomical evidence also suggests that Homo erectus lacked language abilities. The spinal column of early Homo erectus was significantly narrower than that of modern humans. This anatomical characteristic implies that Homo erectus had fewer nerves to control the subtle movements of the rib cages that are required for the production of spoken language. This question may remain unanswered, because, unlike stone tools, spoken words never become part of the archaeological record.
The skulls and teeth of early African populations of middle Homo differed subtly from those of later H. erectus populations from China and the island of Java in Indonesia. H. ergaster makes a better candidate for an ancestor of the modern human line because Asian H. erectus has some specialized features not seen in some later humans, including our own species. H. heidelbergensis has similarities to both H. erectus and the later species H. neanderthalensis, although it may have been a transitional species between middle Homo and the line to which modern humans belong.
The Homo’s ergaster probably first evolved in Africa around two million years ago. This species had a rounded cranium with a brain size of between 700 and 850 cu cm (49 to 52 cu in), a prominent brow ridge, small teeth, and many other features that it shared with the later H. erectus. Many paleoanthropologists consider H. ergaster a good candidate for an ancestor of modern humans because it had several modern skull features, including relatively thin cranial bones. Most H. ergaster fossils come from the time range of 1.8 million to 1.5 million years ago.
The most important fossil of this species yet found is a nearly complete skeleton of a young male from West Turkana, Kenya, which dates from about 1.55 million years ago. Scientists determined the sex of the skeleton from the shape of its pelvis. They also determined from patterns of tooth eruption and bone growth that the boy had died when he was between nine and 12 years old. The Turkana boy, as the skeleton is known, had elongated leg bones and arm, leg, and trunk proportion that essentially match those of a modern humans, in sharp contrast with the apelike proportions of H. habilis and Australopithecus afarensis. He appears to have been quite tall and slender. Scientists estimate that, had he grown into adulthood, the boy would have reached a height of 1.8 m (6 ft) and a weight of 68 kg (150 lb). The anatomy of the Turkana boy indicates that H. ergaster was particularly well adapted for walking and perhaps for running long distances in a hot environment (a tall and slender body dissipates heat well) but not for any significant amount of tree climbing
The oldest humanlike fossils outside of Africa have also been classified as H. ergaster, dated around 1.75 million year’s old. These finds, from the Dmanisi site in the southern Caucasus Mountains of Georgia, consist of several crania, jaws, and other fossilized bones. Some of these are strikingly like East African H. ergaster, but others are smaller or larger than H. ergaster, suggesting a high degree of variation within a single population.
H. ergaster, H. rudolfensis, and H. habilis, in addition to possibly two robust Australopiths, all might have coexisted in Africa around 1.9 million years ago. This finding goes against a traditional paleoanthropological view that human evolution consisted of a single line that evolved progressively over time—an australopith species followed by early Homo, then middle Homo, and finally H. sapiens. It appears that periods of species diversity and extinction have been common during human evolution, and that modern H. sapiens has the rare distinction of being the only living human species today.
Although H. ergaster appears to have coexisted with several other human species, they probably did not interbreed. Mating rarely succeeds between two species with significant skeletal differences, such as H. ergaster and H. habilis. Many paleoanthropologists now believe that H. ergaster descended from an earlier population of Homo - perhaps one of the two known species of early Homo - and that the modern human line descended from H. ergaster.
Sophisticated dating techniques combined with new fossil discoveries suggest that skeletal remains unearthed in Africa in 1995 come from the earliest known human ancestors to walk upright, according to a report published in the journal Nature on May 7, 1998.
Researchers said the new findings indicated that Bipedalism (walking on two legs) emerged 4.07 million to 4.17 million years ago, about 500,000 years earlier than was previously believed. Experts said the new research had important implications for the study of human origins because Bipedalism is widely considered a key evolutionary adaptation that set the human lineage apart from that of other primates.
The new findings are based on fossils found three years ago in northern Kenya near Lake Turkana. Scientists identified the fossils as belonging to a newly discovered prehumans species, Australopithecus anamensis, a creature with apelike teeth and jaws, long arms, and a small brain.
Initial efforts to determine the age of the sediments in which the fossils were discovered failed, raising doubts about the fossils' antiquity. In addition, a lower-leg bones provide for critical evidence of Bipedalism was found in a different sedimentary layer, suggesting the bone could be younger or from a different species.
Nevertheless, a new dating effort, led by anthropologist Meave G. Leakey of the National Museums of Kenya, used an argon-dating analysis technique that examined crystals in sedimentary volcanic ash. Researchers said the technique showed the lower-leg bone to be a “little” younger than the other fossils that were dated at 4.07 million to 4.17 million years ago. This finding indicated the remains belonged to the same species. The dating analysis was further supported by the subsequent discovery of dozens of new fossils in the area, the researchers said.
Before the discovery of Australopithecus anamensis, the earliest known bipedal human ancestor was Australopithecus afarensis, the famous “Lucy” skeleton discovered in Ethiopia in 1974 and estimated to be three million to 3.7 million years old. Based on the new findings, some scientists believe that A. anamensis may be the most ancient species of australopithecine.
One of the earliest defining human traits, Bipedalism - walking on two legs as the primary form of locomotion - evolved more than four million years ago. Other important human characteristics - such as a large and complex brain, the ability to make and use tools, and the capacity for language - developed more recently. Many advanced traits - including complex symbolic expression, such as art, and elaborate cultural diversity - emerged mainly during the past 100,000 years.
Few books have rocked the world the way that. On the Origin of Species did. Influenced in part by British geologist Sir Charles Lyell’s theory of a gradually changing earth, British naturalist Charles Darwin spent decades developing his theory of gradual evolution through natural selection before he published his book in 1859. The logical - and intensely controversial - extension of Darwin’s theory was that humans, too, evolved through the ages. For people who accepted the biblical view of creation, the idea that human beings shared common roots with lower animals was shocking. In this excerpt form. On the Origin of Species, Darwin carefully sidesteps the issue of human evolution (as he did throughout the book), focussing instead on competition and adaptation in lower animals and plants
Humans are primates. Physical and genetic similarities show that the modern human species, Homo sapiens, has a very close relationship to another group of primate species, the apes. Humans and the so-called great apes (large apes) of Africa - chimpanzees (including bonobos, or so-called pygmy chimpanzees) and gorillas - share a common ancestor that lived sometime between eight million and six million years ago. The earliest humans evolved in Africa, and much of human evolution occurred on that continent. The fossils of early humans who lived between six million and two million years ago come entirely from Africa. Humans and great apes of Africa share a common ancestor that lived between eight million and five million years ago.
Most scientists distinguish among 12 to 19 different species of early humans. Scientists do not all agree, however, about how the species are related or which ones simply died out. Many early human species—probably the majority of them - left no descendants. Scientists also debate over how to identify and classify particular species of early humans, and about what factors influenced the evolution and extinction of each species.
Tree of Human Evolution Fossil evidence indicates that the first humans evolved from ape ancestors at least six million years ago. Many species of humans followed, but only some left descendants on the branch leading to Homo sapiens. In this slide show, white skulls represent species that lived during the time indicated; gray skulls represent extinct human species.
Early humans first migrated out of Africa into Asia probably between two million and 1.7 million years ago. They entered Europe in some respects later, generally within the past one million years. Species of modern humans populated many parts of the world much later. For instance, people first came to Australia probably within the past 60,000 years, and to the Americas within the past 35,000 years. The beginnings of agriculture and the rise of the first civilizations occurred within the past 10,000 years.
The scientific study of human evolution is called Paleoanthropology. Paleoanthropology is a subfield of anthropology, the study of human culture, society, and biology. Paleoanthropologists search for the roots of human physical traits and behaviour. They seek to discover how evolution has shaped the potentials, tendencies, and limitations of all people. For many people, Paleoanthropology is an exciting scientific field because it illuminates the origins of the defining traits of the human species, as well as the fundamental connections between humans and other living organisms on Earth. Scientists have abundant evidence of human evolution from fossils, artifacts, and genetic studies. However, some people find the concept of human evolution troubling because it can seem to conflict with religious and other traditional beliefs about how people, other living things, and the world came to be. Yet many people have come to reconcile such beliefs with the scientific evidence.
Modern and Early Humans have undergone major anatomical changes over the course of evolution. This illustration depicts Australopithecus afarensis (centre), the earliest of the three species; Homo erectus (left), an intermediate species; and Homo sapiens (right), a modern human. H. erectus and modern humans are much taller than A. afarensis and have flatter faces and much larger brains. Modern humans have a larger brain than H. erectus and almost flat face beneath the front of the braincase. National Geographic Society/John Sibbick
All species of organisms originate through the process of biological evolution. In this process, new species arise from a series of natural changes. In animals that reproduce sexually, including humans, the term species refers to a group whose adult members regularly interbreed, resulting in fertile offspring—that is, offspring themselves capable of reproducing. Scientists classify each species with a unique, two-part scientific names. In this system, modern humans are classified as Homo sapiens.
The mechanism for evolutionary change resides in genes—the basic units of heredity. Genes affect how the body and behaviour of an organism develop during its life. The information contained in genes can be change—a process known as mutation. The way particular genes are expressed - how they affect the body or behaviour of an organism - can also change. Over time, genetic change can alter a species’s overall way of life, such as what it eats, how it grows, and where it can live.
Genetic changes can improve the ability of organisms to survive, reproduce, and, in animals, raise offspring. This process is called adaptation. Parents pass adaptive genetic changes to their offspring, and ultimately these changes become common throughout a population—a group of organisms of the same species that share a particular local habitat. Many factors can favour new adaptations, but changes in the environment often play a role. Ancestral human species adapted to new environments as their genes changed, altering their anatomy (physical body structure), physiology (bodily functions, such as digestion), and behaviour. Over long periods, evolution dramatically transformed humans and their ways of life.
Geneticists estimate that the human line began to diverge from that of the African apes between eight million and five million years ago (paleontologists have dated the earliest human fossils to at least six million years ago). This figure comes from comparing differences in the genetic makeup of humans and apes, and then calculating how long it probably took for those differences to develop. Using similar techniques and comparing the genetic variations among human populations around the world, scientists have calculated that all people may share common genetic ancestors that lived sometime between 290,000 and 130,000 years ago.
Humans belong to the scientific order named Primates, a group of more than 230 species of mammals that also includes lemurs, lorises, tarsiers, monkeys, and apes. Modern humans, early humans, and other species of primates all have many similarities as well as some important differences. Knowledge of these similarities and differences helps scientists to understand the roots of many human traits, as well as the significance of each step in human evolution.
The origin of our own species, Homo sapiens, is one of the most hotly debated topics in Paleoanthropology. This debate centers on whether or not modern humans have a direct relationship to H. erectus or to the Neanderthals, a well-known, more modern group of humans who evolved within the past 250,000 years. Paleoanthropologists commonly use the term anatomically modern Homo sapiens to distinguish people of today from these similar predecessors.
Traditionally, paleoanthropologists classified as Homo sapiens any fossil human younger than 500,000 years old with a braincase larger than that of H. erectus. Thus, many scientists who believe that modern humans descend from a single line dating back to H. erectus use the name archaic Homo sapiens to refer to a wide variety of fossil humans that predate anatomically modern H. sapiens. The term archaic denotes a set of physical features typical of Neanderthals and other species of late Homo before modern Homo sapiens. These features include a combination of a robust skeleton, a large but low braincase (positioned reasonably behind, than over, the face), and a lower jaw lacking a prominent chin. In this sense, Neanderthals are sometimes classified as a subspecies of archaic H. sapiens - H. Sapiens neanderthalensis. Other scientists think that the variation in archaic fossils existently falls into clearly identifiable sets of traits, and that any type of human fossil exhibiting a unique set of traits should have a new species name. According to this view, the Neanderthals belong to their own species, H. neanderthalensis.
The Neanderthals lived in areas ranging from western Europe through central Asia from about 200,000 to about 28,000 years ago. The name Neanderthal (sometimes spelled Neanderthal) comes from fossils found in 1856 in the Feldhofer Cave of the Neander Valley in Germany (tal - a modern form of thal - means “valley” in German). Scientists realized several years later that prior discoveries - at Engis, Belgium, in 1829 and at Forbes Quarry, Gibraltar, in 1848 - also represented Neanderthals. These two earlier discoveries were the first early human fossils ever found. In the past, scientists claimed that Neanderthals differed greatly from modern humans. However, the basis for this claim came from a faulty reconstruction of a Neanderthal skeleton that showed it with bent knees and a slouching gait. This reconstruction gave the common but mistaken impression that Neanderthals were dim-witted brutes who lived a crude lifestyle. On the contrary, Neanderthals, like the species that preceded them, walked fully upright without a slouch or bent knees. In addition, their cranial capacity was quite large at about 1,500 cu cm (about 90 cu in), larger on average than that of modern humans. (The difference probably relates to the greater muscle mass of Neanderthals as compared with modern humans, which usually correlates with a larger brain size.)
Compared with earlier humans, Neanderthals had a high degree of cultural sophistication. They appear to have performed symbolic rituals, such as the burial of their dead. Neanderthal fossils - including a number of fairly complete skeletons—are quite common compared with those of earlier forms of Homo, in part because of the Neanderthal practice of intentional burial. Neanderthals also produced sophisticated types of stone tools known as Mousterian, which involved creating blanks (rough forms) from which several types of tools could be made.
Along with many physical similarities, Neanderthals differed from modern humans in several ways. The typical Neanderthal skull had a low forehead, a large nasal area (suggesting a large nose), a forward-projecting nasal and cheek region, a prominent brow ridge with a bony arch over each eye, a nonprojecting chin, and obvious space behind the third molar (in front of the upward turn of the lower jaw).
Neanderthal and Modern Human Skulls the skull of Homo neanderthalensis (left) differs considerably from that of anatomically modern humans, or Homo sapiens (right). Neanderthals had thick-walled skulls, sloping foreheads, and heavy brow ridges. This contrasts with the thin-walled skulls, high foreheads, and flat faces of modern humans. Neanderthals also had more pronounced and powerful jaws but less of a chin than do modern humans.
Neanderthal also had a more heavily built and large-boned skeleton than do modern humans. Other Neanderthal skeletal features included a bowing of the limb bones in some individuals, broad scapulae (shoulder blades), hip joints turned outward, a long and thin pubic bone, short lower leg and arm bones relative to the upper bones, and large surfaces on the joints of the toes and limb bones. Together, these traits made a powerful, compact body of short stature—males averaged 1.7 m (5 ft 5 in) tall and 84 kg (185 lb), and females averaged 1.5 m (5 ft) tall and 80 kg (176 lb).
The short, stocky build of Neanderthals conserved heat and helped them withstand extremely cold conditions that prevailed in temperate regions beginning about 70,000 years ago. The last known Neanderthal fossils come from western Europe and date from approximately 36,000 years ago.
At the same time as Neanderthal populations grew in number in Europe and parts of Asia, other populations of nearly modern humans arose in Africa and Asia. Scientists also commonly refer to these fossils, which are distinct from but similar to those of Neanderthals, as archaic. Fossils from the Chinese sites of Dali, Maba, and Xujiayao display the long, low cranium and large face typical of archaic humans, yet they also have features similar to those of modern people in the region. At the cave site of Jebel Irhoud, Morocco, scientists have found fossils with the long skull typical of archaic humans but also the modern traits modern of measure have higher forehead and flatter midface. Fossils of humans from East African sites older than 100,000 years - such as Ngaloba in Tanzania and Eliye Springs in Kenya - also seem to show a mixture of archaic and modern traits.
Ancient Human Footprints the oldest known footprints of an anatomically modern human are embedded in rock north of Cape Town, South Africa. Geologist David Roberts and paleoanthropologists Lee Berger announced the discovery of the footprints in August 1997. A human being made the footprints about 117,000 years ago by walking through wet sand, which eventually hardened into rock.
The oldest known fossils that possess skeletal features typical of modern humans date from between 130,000 and 90,000 years ago. Several key features distinguish the skulls of modern humans from those of archaic species. These features include a much smaller brow ridge, if any; a globe-shaped braincase; and a flat or only projecting face of reduced size, located under the front of the braincase. Among all mammals, only humans have a face positioned directly beneath the frontal lobe (forward-most area) of the brain. As a result, modern humans tend to have a higher forehead than did Neanderthals and other archaic humans. The cranial capacity of modern humans ranges from about 1,000 to 2,000 cu cm (60 to 120 cu in), with the average being about 1,350 cu cm (80 cu in).
Scientists have found both fragmentary and nearly complete cranial fossils of early anatomically modern Homo sapiens from the sites of Singha, Sudan; Omo, Ethiopia; Klasies River Mouth, South Africa; and Skhûl Cave, Israel. Based on these fossils, many scientists conclude that modern H. sapiens had evolved in Africa by 130,000 years ago and started spreading to diverse parts of the world beginning on a route through the Near East sometime before 90,000 years ago.
The 1994 discovery in Sierra de Atapuerca, Spain, of well-preserved hominid bones pushed back the date for the arrival in Europe of our early human ancestors to 800,000 years ago. Anthropology professor Brian Fagan discusses these and other recent findings about the first members of the human family to live in Europe, and he dispels the widespread myth that Neanderthals were dumb and brutish.
Paleoanthropologists are engaged in an ongoing debate about where modern humans evolved and how they spread around the world. Differences in opinion rest on the question of whether the evolution of modern humans took place in a small region of Africa or over a broad area of Africa and Eurasia. By extension, opinions differ as to whether modern human populations from Africa displaced all existing populations of earlier humans, eventually resulting in their extinction. Those who think modern humans originated only in Africa and then spread around the world support what is known as the out of Africa hypothesis. Those who think modern humans evolved over a large region of Eurasia and Africa support the so-called multi-regional hypothesis.
Researchers have conducted many genetic studies and carefully assessed fossils to determine which of these hypotheses agrees more with scientific evidence. The results of this research do not entirely confirm or reject either one. Therefore, some scientists think a compromise between the two hypotheses is the best explanation. The debate between these views has implications for how scientists understand the concept of race in humans. The question raised is whether the physical differences among modern humans evolved deep in the past or relatively recently.
Scientists reported in the May 16, 1996, issued of the journal Nature that later Neanderthals likely interacted, perhaps even traded goods, with Cro-Magnons, their anatomically modern human neighbours. Researchers in Arcy-sur-Cure, France, 35 km (22 mi) southeast of Auxerre, said they found hominid fossils alongside bone and ivory jewellery nearly identical to artifacts attributed to anatomically modern humans.
The fossils were found in Arcy-sur-Cure long ago, but scientists could not determine to which human species the bones belonged. The shape of the inner ear gave anthropologists a clue that the 34,000-year-old fossil remains found decades ago were from a Neanderthal, not a modern human. The ear morphology may also shed light on the relationship of Neanderthals to humans of today.
The ornaments found at the Arcy site included a bone ring, grooved animal teeth, and animal claws with small holes made at one end, presumably so they could be strung on a cord and hung around the neck. They resemble jewellery found at sites in northern Spain and central and southwestern France where Cro-Magnons lived. Anthropologists Jean-Jacques Hublin of the Musée de l'Homme in Paris, France, and Fred Spoor of University College in London, England, the coauthors of the report, concluded that the presence of jewellery at the Arcy site nearly identical to jewellery at the Cro-Magnon sites indicated that Neanderthals probably traded with Cro-Magnons rather than imitated the style of their contemporary neighbours. The resemblance was too close in appearance to nearby Cro-Magnon finds for imitation, they believe. Anatomically modern humans first arrived in Europe about 40,000 years ago.
The relationship of Neanderthals to modern humans has long been a topic of scientific debate. The fossil record suggests Neanderthals disappeared from 30,000 to 40,000 years ago. Neanderthals characteristics differ most obviously from anatomically modern humans in the formation of the skull and face. The Neanderthal had a sloping forehead, no chin, protruding browridges, large teeth, and strong jaw muscles. The brains of Neanderthals were larger than those of modern humans. Aside from the face, the Neanderthals had thicker bones and larger musculature, long bodies and short legs. Some of the Neanderthal's features, especially body proportion, were cold-weather adaptations similar to those developed by modern people living in arctic conditions, such as the Inuit.
Hublin and Spoor used high-resolution, computerized X rays to scrutinize a temporal (side) bone from the skull of a one-year-old Neanderthal. They found that the ear canals-known as the labyrinth-within the bone was distinctly different in size and location from the same bone in Homo erectus, an early human ancestor, and anatomically modern humans. The labyrinth consists of three hollow rings and is involved in maintaining balance.
Some scientists classify the Neanderthal as a separate species, Homo neanderthalensis. Because the features of the Neanderthal's labyrinth do not exist in modern humans, the scientists believe that the muscular hominid belongs to a separate species, or at least is not an ancestor of modern humans. Some experts believe that Neanderthals evolved from archaic Homo sapiens into an evolutionary dead end. Other researchers have speculated that later Neanderthals may have interbred with Cro-Magnons, but Hublin argues that his new evidence does not support that theory. In their report to Nature, Hubin and Spoor said their findings did not show any trend toward more modern human characteristics.
Archives consist of articles that originally appeared in Collier's Year Book because they were published shortly after events occurred, they reflect the information available at that time. Cross references refer to Archive articles of the same year. Archaeology Top stories in archaeology in 1995 included new dates for the Neanderthals and the discovery of the frozen bodies of a Scythian equestrian and an Inca woman. Last Neanderthals. New dates from Zafarraya Cave in southern Spain suggest that Neanderthals were alive millennia after scholars assumed they had become extinct. The dates also suggest that Neanderthals coexisted with modern humans in Western Europe for 10,000 years or more, rather than being replaced quickly by overwhelmingly superior modern groups, as many archaeologists have argued. Samples of animal bones and teeth found with Neanderthal remains and artifacts were subjected to both carbon and thorium/uranium testing, producing dates of around 30,000 years ago. In northern Spain stone tools of a type generally associated with modern humans appeared between 40,000 and 38,000 years ago. Elsewhere in Europe, Neanderthal and modern human populations mixed, but in southern Spain, Neanderthals survived without strong biological or cultural interaction with the newcomers, probably because they were isolated. The existence of a Neanderthal population in southern Spain long after modern humans arrived in the north makes it unlikely that modern humans reached Western Europe from Africa via the Strait of Gibraltar. Frozen Bodies. A frozen Scythian equestrian, dated to around 500 Bc, was found in Siberia's Altai Mountains. The man, 25-30 years of age, was buried with his horse, bow and arrows, an ax, and a knife. He was wearing a thick wool cap, high leather boots, and a coat of marmot and sheepskin. On his right shoulder is a large tattoo of a stag. The horse's harness was decorated with wood carvings of griffins and animals covered in gold foil. The horseman's body, like the body of a richly attired woman discovered in the same area in 1993, had been buried in a log-lined chamber under more than 2 metres (7 feet) of permafrost. The horseman's mummy was moved to a Moscow lab for preservation. In southern Peru the frozen body of an Inca woman of 12-14 years of age, probably a sacrificial victim, was found near the summit of a 6,300-metre (20,700-foot) peak. The remains, dated around Ad. 1500, were discovered 60 metres (200 feet) below a stone sanctuary. The peak is usually ice-covered, but the recent eruption of a nearby volcano had blanketed it with ash. The dark-coloured ash absorbed the sun's warmth instead of reflecting it as the ice had, and the ice melted. Two more bodies were later found farther down the slope, along with the remains of a camp used by the sanctuary's builders and priests. Several small figurines of gold, silver, gold-copper alloy, and oyster-like shell were found near the girl's body, and two had been wrapped in the layers of wool and cotton cloth in which it was bundled. The body had an elaborate feather headdress. The most important aspect of the find is that the bodies were frozen, providing an opportunity to study Inca diet and health. Early Bone Points From Africa. Archaeologists dated barbed bone points found in eastern Zaire to 90,000 years or older. The ability to make such tools at this early date supports an African origin of behaviourally as well as biologically modern humans, the archaeologists said. Barbed points do not occur before 14,000 to 12,000 years ago at sites in Eurasia. The barbed points, and unbarbed points and a flat dagger-shaped object with rounded edges, came from three sites at Katanda in the Semliki River valley. Dating of the immediately overlying sands and hippo teeth found in them suggests an age of 80,000 to 90,000 years ago for the site. The barbed points were found with mammal and fish remains, of which catfish were most abundant. The catfish were probably caught during the rainy season when they spawned on the inundated floodplain and were easy to catch. The Katanda sites indicate that a complex bone industry and seasonal use of aquatic resources had developed by 90,000 years ago, following a specialized subsistence pattern most often associated in Europe with the end of the Ice Age nearly 80,000 years later. Earliest Weaving. Impressions of woven fabric on four fragments of clay from Pavlov I, an Upper Paleolithic site in the Czech Republic, have proved to be the earliest evidence of weaving ever found. The fragments were carbon dated in 1995 to between 26,980 and 24,870 years ago. The dates are at least 7,000 to 10,000 years earlier than those of any other evidence of weaving. Two of the better-preserved specimens show tightly spaced rows characteristic of a finely woven bag or mat. The fineness and the method of weaving used, known as twining, suggested that the material may have been produced using a loom and that the weavers were accomplished and not experimenting with a new technology. This means that the actual advent of weaving may be even earlier than the date of the Pavlov specimens. The impressions from Pavlov I show that a wide range of items, such as baskets, nets, and snares, were likely to have been available to the hunter-gatherers of the Upper Paleolithic. Chauvet Art. The spectacular decorated Grotte Chauvet in southern France, whose discovery was announced in January, has proved to have the world's oldest known cave paintings, carbon dated to more than 30,000 years ago. The cave also contains human and bear footprints, flints, bones, and hearths. Submarines and Archaeology. The Confederate vessel Hunley, the first submarine ever to sink a warship in combat, was discovered in May off the coast of Charleston, SC. Famous for its attack on the U.S.S. Housatonic during the American Civil War, the submarine went down shortly after sinking the ship on February 17, 1864. The Hunley was made from an iron locomotive boiler and carried a copper canister filled with 40 kilograms (90 pounds) of black powder at the end of a long spar. Manned by volunteers who powered its hand-cranked propeller, the Hunley placed its charge alongside the target and then backed up, detonating the explosive with a long cord that triggered the firing mechanism. The U.S. Navy announced in 1995 that the NR-1, a formerly classified submarine, would be used to search the Mediterranean seafloor for ancient shipwrecks. The submarine's windows and extensive light and sonar arrays make it perfect for searching for ancient wrecks, and its remote-controlled arm can retrieve objects. The NR-1, the world's smallest nuclear submarine, will enable archaeologists to study the open-water trade routes of antiquity, not just the coastal routes. Its first archaeological mission will be to explore the trade route between Carthage, on the North African coast, and Rome. The discovery in 1995 of the Japanese submarine I-52, which was sunk on June 23, 1944, deepened concerns about the growing accessibility of the deep oceans. American and British treasure hunters were in a race to find the sub and its cargo, 2 metric tons of gold. Both groups hired Russian research vessels with sophisticated sonar and photographic capabilities. In May the American group found the submarine 5,000 metres (17,000 feet) down in the mid-Atlantic. The discoverer stated that the gold, valued at $25 million, would be recovered with the least disturbance possible to the vessel, which may still hold the remains of 109 men. The Japanese government may retain title to both vessel and contents. Nonetheless, the implications are clear: anyone with sufficient financial backing can locate and, if the person is unscrupulous, pillage shipwrecks - ancient, medieval, or modern. Egyptian Tombs. Important discoveries were made in 1995 at both well-known and newly found cemeteries in Egypt. At Saqqara, near Cairo, French archaeologists discovered the necropolis of three queens of the Sixth Dynasty Pharaoh Pepi I (2332-2283 Bc). A pyramid 45 metres (150 feet) high found buried in sand at Saqqara is the tomb of Queen Meretites, a descendant of Pepi I. It may provide information on a turbulent period at the end of the dynasty when powerful governors paid only nominal allegiance to the pharaoh. Egyptian and Canadian archaeologists located a vast pre-dynastic cemetery at Tell Hassan Dawoud, 100 kilometres (60 miles) east of Cairo, dating to 3000 Bc or earlier. Many of the tombs yielded gold, marble, and ceramic artifacts. Not all of the burials had grave offerings, however, suggesting that Egypt's society was strongly stratified 500 years before the pharaohs. The largest tomb ever found in Egypt's Valley of the Kings was partly explored in 1995. The tomb was the burial place of many of the 100 or more offspring of Rameses II, who reigned around 1279-1212 Bc. Artifacts recovered from the tomb bear the names of at least four of his sons, and the name of the firstborn, Amon-her-khepeshef, are painted on a wall. Until this discovery little was known about most of the pharaoh's offspring. The tomb is unlikely to hold any great treasure, since a papyrus in Turin records its robbery in 1150 Bc. Its chief importance is the information it may yield about family burials and tomb plans of New Kingdom royalty. Syrian Bronze Age Cemetery. Archaeologists working at Tell es-Sweyhat on the Euphrates River in northern Syria discovered an intact tomb in what may be an unplundered cemetery containing up to 150 such tombs. Investigation of a number of tombs could provide a sample of human remains large enough to determine biological relationships and social organization of the people through DNA analysis. A large sample would also allow study of diet and disease in the population. The tomb, dated around 2500-2250 Bc, held the remains of several individuals. More than 100 ceramic vessels were in the tomb, along with incised bone, beads, and shells. Copper and bronze objects included daggers, axes, and a javelin. Bones of numerous pigs, sheep, goats, and cows in the tomb are the remains of funerary offerings. Bird eggs had been placed in the eye sockets of one animal skull
Still, it was the Primates, of whom are an order of mammals that includes humans, apes, which are the closest living relatives to humans, monkeys, and some less familiar mammals, such as tarsiers, lorises, and lemurs. Humans and other primates share a common evolutionary descent. For this reason, primates have always fascinated scientists because their physical features, social organization, behavioural patterns, and fossil remains provide clues about our earliest human ancestors.
Primates evolved from tree-dwelling ancestors. Although some species, such as humans, have since taken to the ground, all primates’ share features that are related to their tree-climbing ancestry. These include arms and legs that can move more freely than those of most other mammals, flexible fingers and toes, forward-facing eyes that can judge distances accurately - a vital aid when moving about high above the ground - and large brains.
Primates live in a wide range of habitats but are restricted by their need for warmth. Most primates live in tropical jungles or dry forests, but some live in dry grasslands, and others have settled in cold, mountainous regions of China and Japan. The world's most northerly primate, the Japanese macaque, has learned to bathe in hot springs to survive through the winter snows. In parts of the tropics, monkeys can be seen within a few miles of busy city centers, but despite this adaptability, the majority of the world’s primates retain a close dependence on trees. Apart from humans, baboons are the only primates that have fully made the transition to life out in the open, and even they instinctively climb to safety if danger threatens.
Some primates, especially the smaller species, are active only at night, or nocturnal, while others are diurnal, active during the day. Most primate species - particularly monkeys - are highly sociable animals, sometimes living in troops of more than 100 members. Smaller primates, especially nocturnal ones, tend to be solitary and secretive.
Primates range in size from quite small to quite large. The world's largest species, the lowland gorilla at 200 kg (400 lb) is more than 6,000 times the weight of the smallest primate, the pygmy mouse lemur from Madagascar. Measuring just 20 cm (8 in) from nose to tail, and weighing about 30 g (1 oz), this tiny animal was first identified about two centuries ago, but was later assumed to be extinct until its rediscovery in 1993.
There are about 235 species of primates. Scientists use more than one way to classify primates, and one system divides the order into two overall groups, or suborders: the prosimians and the anthropoids.
The prosimians, or "primitive primates," make up the smaller of these two groups, with about 60 species, and include lemurs, pottos, galagos, lorises, and, in some classification systems, tarsiers. Lemurs are only found on the islands of Madagascar and Comoros, where they have flourished in isolation for millions of years. Pottos and galagos are found in Africa, while lorises and tarsiers are found in southeast Asia. Typical prosimians are small to medium-sized mammals with long whiskers, pointed muzzles, and well-developed senses of smell and hearing. Most prosimians are nocturnal, although in Madagascar some of the larger lemurs are active by day.
In the past, tree shrews were often classified as primates, but their place in mammal classification has been the subject of much debate. Today, based on reproductive patterns and on new fossil evidence, most zoologists classify them in an order of their own, the Scandentia.
The remainder of the world's primates makes up the anthropoid, or “humanlike” suborder, which contains about 175 species. This group consists of humans, apes, and monkeys. Most anthropoids, apart from baboons, have flat faces and a relatively poor sense of smell. With a few exceptions, anthropoids are almost always active during the day, and they find their food mainly by sight.
Evolution has had a marked effect on the thumbs and big toes of primates. In most mammals, these digits bend in the same plane as the other fingers and toes. Nevertheless, in many primates, the thumbs or big toes are opposable, meaning that they are set apart in a way that permits them to meet the other digits at the tips to form a circle. This enables primates to grip branches, and equally importantly, pick up and handle small objects. Instead of having claws, most primates have flat nails that cover soft, sensitive fingertips—another adaptation that helps primates to manipulate objects with great dexterity.
Primate skulls show several distinctive features. One of these is the position of the eyes, which in most species is on the front of the skull looking forward, rather than on the side of the skull looking to the side as in many other mammals. The two forward-facing eyes have overlapping fields of view, which give primates stereoscopic vision. Stereoscopic vision permits accurate perception of distance, which is helpful for handling food or swinging from branch to branch high above the ground. Another distinctive feature of primate skulls, in anthropoids particularly, is the large domed cranium that protects the brain. The inside surface of this dome clearly shows the outline of an unusually large brain - one of the most remarkable characteristics of this group. The shapes of anthropoid brains are different from other mammals; the portion of the brain devoted to vision is especially large, while the portion devoted to smell is comparatively small.
The primate order includes a handful of species that live entirely on meat (carnivores) and a few that are strict vegetarians (herbivores), but it is composed chiefly of animals that have varied diets (omnivores). The carnivorous primates are the four species of tarsiers, which live in Southeast Asia. Using their long back legs, these pocket-sized nocturnal hunters leap on their prey, pinning it down with their hands and then killing it with their needle-sharp teeth. Tarsiers primarily eat insects but will also eat lizards, bats, and snakes.
Other prosimians, such as galagos and mouse lemurs, also hunt for insects, but they supplement their diet with different kinds of food, including lizards, bird eggs, fruit, and plant sap. This opportunistic approach to feeding is seen in the majority of monkeys and in chimpanzees. Several species of monkeys, and chimpanzees, but not the other apes, have been known to attack and eat other monkeys. Baboons, the most adept hunters on the ground, often eat meat and sometimes manage to kill small antelope.
Primates display a wide range of mating behaviours. Solitary primates, such as aye-ayes and orangutans, have relatively simple reproductive behaviour. Within the territory that each male controls, several females live, each with their own territory. The male mates with any females within his territory that are receptive. Other species, such as gibbons, form small family groups consisting of a monogamous pair and their young. Gorillas form harems, in which one adult male lives with several adult females and their young. Among social primates, breeding can be complicated by the presence of many adults. Males may cooperate in defending their troop's territory, but they often fight each other for the chance to mate. In some species, only the dominant male mates with the females in the group. Chimpanzee females mate promiscuously with several adult males, although they usually pair up with one of the high-ranking males during the final few days of estrus, spending all of their time together and mating together exclusively.
Primates have the most highly developed brains in the animal kingdom, rivalled only by those of dolphins, whales, and possibly elephants. Anthropoid primates in particular are intelligent and inquisitive animals that are quick to learn new patterns of behaviour. This resourcefulness enables them to exploit a wide range of foods and may help them to escape attacks by predators.
Many zoologists believe that primates' large brains initially evolved in response to their tree-dwelling habits and their way of feeding. Anthropoid primates, which have the largest brains, live in a visual world, relying on sight to move about and to locate and manipulate food. Unlike smell or hearing, vision generates a large amount of complex sensory information that has to be processed and stored. In primate brains, these operations are carried out by a portion of the brain called the cerebral cortex, which evolved into such a large structure that the rest of the brain is hidden beneath it. Some unrelated mammals, such as squirrels, also live in trees, but they have less-developed eyesight and much smaller brains.
Increased brainpower has had impressive effects on the way primates live. It has helped them to move about and find food as well as enabled them to develop special skills. One of the most remarkable of these is toolmaking, seen in chimpanzees and, to a far greater extent, in humans. Toolmaking, as opposed to simple tool use, involves a preconceived image of what the finished tool should look like - something that is only possible with an advanced brain.
The intelligence of primates is also evident in their social behaviour. For species that live in groups, daily life involves countless interactions with relatives, allies, and rivals. Mutual cleaning and grooming of the fur, which removes parasites, helps to reinforce relationships, while threats - sometimes followed by combat - maintain the hierarchy of dominance that permeates typical primate troops.
Primates use a variety of methods to communicate. In solitary prosimians, when animals are not within sight of each other, communication is often accomplished by using scents. Such animals use urine, faeces, or special scent glands to mark territory or to communicate a readiness to mate. In social anthropoids, visual and vocal signals are much more important. Most monkeys and apes communicate with a complex array of facial expressions, some of which are similar to the facial expressions used by humans
The earliest fossils of primates that have been discovered date from the end of the Cretaceous Period, about 65 million years ago. These early fossils include specimens of a species called Notharctus, which resembles today's lemurs and had a long pointed snout. The ancestors of another prosimian group, the tarsiers, are known from fossils that date back to the early Eocene Epoch, about 50 million years ago. In 1996 researchers in China recovered fossil bones of a primitive primate no bigger than a human thumb. The animal, named Eosimias, lived 45 million years ago. Many scientists believe that Eosimias is an example of a transitional animal in the evolution of prosimians to anthropoids
The origin of anthropoids has proven to be difficult to pin down. A single anthropoid fossil has been found that may come from the Eocene Epoch, but conclusive fossil evidence of anthropoids does not appear until the Oligocene Epoch, which began 38 million years ago. These early anthropoids belonged to a lineage that led to the catarrhine primates - the Old World monkeys, apes, and humans. The platyrrhine primates, which include all New World monkeys, are presumed to have diverged from the Old World monkeys during the Eocene Epoch. They evolved in isolation on what was then the island continent of South America. Genetic analysis shows that New World monkeys clearly share a common ancestry with the catarrhines, which means that they must have reached the island continent from the Old World. Exactly how they did this is unclear. One possibility is that they floated across from Africa on logs or rafts of vegetation, journeying across an Atlantic Ocean that was much narrower than it is today
Of all primate groups, the apes and the direct ancestors of humans have been the most intensively studied. One key question concerns when the two groups diverged. Based on the comparisons of genes and the structure of body parts, scientists think that the line leading to the orangutan diverged from the one leading to humans about 12 million years ago. The ancestral line leading to chimpanzees did not diverge until more recently, probably between 5 and 7 million years ago. This evidence strongly suggests that chimpanzees are our closest living relatives. Apes and monkeys also play an important role in the field of medical research. Because their body systems work very much like our own, new vaccines and new forms of surgery are sometimes tried on apes and monkeys before they are approved for use on humans. Species that are most often used in this way include chimpanzees, baboons, and rhesus monkeys. This kind of animal experimentation has undoubtedly contributed to human welfare, but the medical use of primates is an increasingly controversial area, particularly when it involves animals captured in the wild.
The species most under threats are those that have been affected by deforestation. This has been particularly severe in Madagascar, the only home of the lemurs, and it is also taking place at a rapid rate in Southeast Asia, threatening gibbons and orangutans. The almost total destruction of Brazil's Atlantic rainforest has proved catastrophic for several species, including the lion tamarins, which are found only in this habitat. Primates are also threatened by collection for the pet trade and by hunting. Illegal hunting is the chief threat facing the mountain gorilla, a rare African subspecies that lives in the politically volatile border region straddling Uganda, Rwanda, and the Democratic Republic of the Congo.
In the face of these threats, urgent action is currently underway to protect many of these endangered species. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) currently forbids the export of many primates, although not all countries have chosen to follow this law. More direct methods of species preservation include habitat protection and captive breeding programs. In some cases - for example, the lion tamarin - these programs have met with considerable success. However, without the preservation of extensive and suitable natural habitats, many primate species are destined for extinction.
Our closest living relative are three surviving species of great apes: the gorilla, the common chimpanzee, And the pygmy chimpanzee (also known as bonobo0). Their confinement to Africa, along with abundant fossil evidence, strongly suggests that they also played the earliest stages of human evolution out in Africa, human history, as something separate from the history of animals, occurring about seven million years ago (estimates range from five to nine million years ago). Around that time, a population of African apes broke off into several populations, of which one preceded to evolve into modern gorillas, a second into the two modern chimps, and the third into humans. The gorilla line apparently split slightly before the split between the chimp and the human lines.
The primate, is the order of mammals that includes humans, apes, which are the closest living relatives to humans, monkeys, and some less familiar mammals, such as tarsiers, lorises, and lemurs. Humans and other primates share a common evolutionary descent. Consequently, primates have always fascinated scientists because their physical features, social organization, behavioural patterns, and fossil remains provide clues about our earliest human ancestors.
Primates evolved from tree-dwelling ancestors. Although some species, such as humans, have since taken to the ground, all primates’ share features that are related to their tree-climbing ancestry. These include arms and legs that can move more freely than those of most other mammals, flexible fingers and toes, forward-facing eyes that can judge distances accurately - a vital aid when moving about high above the ground - and large brains.
Primates live in a wide range of habitats but are restricted by their need for warmth. Most primates live in tropical jungles or dry forests, but some live in dry grasslands, and others have settled in cold, mountainous regions of China and Japan. The world's most northerly primate, the Japanese macaque, has learned to bathe in hot springs to survive through the winter snows. In parts of the tropics, monkeys can be seen within a few miles of busy city centres, but despite this adaptability, most of the world’s primates retain a close dependence on trees. Apart from humans, baboons are the only primates that have fully made the transition to life out in the open, and even they instinctively climb to safety if danger threatens.
Some primates, especially the smaller species, are active only at night, or nocturnal, while others are diurnal, active during the day. Most primate species - particularly monkeys - are highly sociable animals, sometimes living in troops of more than 100 members. Smaller primates, especially nocturnal ones, tend to be solitary and secretive.
Primates range in size from quite small to quite large. The world's largest species, the lowland gorilla at 200 kg. (400 lb.) is more than 6,000 times the weight of the smallest primate, the pygmy mouse lemur from Madagascar. Measuring only 20 cm. (8 in.) from nose to tail, and weighing about 30 g. (1 oz.), this tiny animal was first identified about two centuries ago, but was later assumed to be extinct until its rediscovery in 1993.
There are about 235 species of primates. Scientists use more than one way to classify primates, and one system divides the order into two overall groups, or suborders: the prosimians and the anthropoids.
The prosimians, or "primitive primates," make up the smaller of these two groups, with about 60 species, and include lemurs, Pontos, galagos, lorises, and, in some classification systems, tarsiers. Lemurs are only found on the islands of Madagascar and Comoros, where they have flourished in isolation for millions of years. Pontos and galagos are found in Africa, while lorises and tarsiers are found in southeast Asia. Typical prosimians are small to medium-sized mammals with long whiskers, pointed muzzles, and well-developed senses of smell and hearing. Most prosimians are nocturnal, although in Madagascar some larger lemurs are active by day.
In the past, tree shrews were often classified as primates, but their place in mammal classification has been the subject of much debate. Today, based on reproductive patterns and on new fossil evidence, most zoologists classify them in an order of their own, the Scandentia.
The remainder of the world's primates makes up the anthropoid, or “humanlike” suborder, which contains about 175 species. This group consists of humans, apes, and monkeys. Most anthropoids, apart from baboons, have flat faces and a poor sense of smell. With a few exceptions, anthropoids are usually active during the day, and they find their food mainly by sight.
Apes are found only in Africa and Asia. They have no tails, and their arms are longer than their legs. Monkeys from Central and South America, known as New World monkeys, have broad noses and nostrils that open sideways. They are called platyrrhine, which means broad-nosed. Monkeys from Africa and Asia, known as Old World monkeys, have narrow noses and nostrils that face downward - a characteristic also seen in apes and humans. Old World Monkeys are called catarrhine, which means downward-nosed.
During evolution, primates have kept several physical features that most other mammals have lost. One of these is the clavicle, or collarbone. In primates, the clavicle forms an important part of the shoulder joint. It helps to stabilize the shoulder, permitting a primate to support its weight by hanging from its arms alone - something that few other mammals can do. Some primates, particularly gibbons and the siamang, use this ability to move through the trees from one branch to another by swinging from arm to arm. This type of locomotion is called the brachiation.
During evolution, many mammals have gradually lost limb bones as they have adapted to different ways of life: horses, for example, have lost all but a single toe on each foot. Nearly all primates, by contrast, have retained a full set of five fingers and toes, and usually these digits have become increasingly flexible as time has gone through. In the aye-aye, a prosimian from Madagascar, the third finger on each hand is long and thin with a special claw at the end. Aye-ayes use these bony fingers to extract insect grubs from bark.
Evolution has affected the thumbs and big toes of primates. In most mammals, these digits bend in the same plane as the other fingers and toes. However, in many primates, the thumbs or big toes are opposable, meaning that they are set apart in a way that permits them to meet the other digits at the tips to form a circle. This enables primates to grip branches, and equally importantly, pick up and handle small objects. Instead of having claws, most primates have flat nails that cover soft, sensitive fingertips—another adaptation that helps primates to manipulate objects with great dexterity.
Tails are absent in humans and apes, but in most monkeys and prosimians, the tail plays a special role in maintaining balance during movement through the treetops. Many New World monkeys have prehensile tails, which can be wrapped around branches, gripping them like an extra hand or foot.
Primate skulls show several distinctive features. One of these is the position of the eyes, which in most species is on the front of the skull looking forward, rather than on the side of the skull looking to the side as in many other mammals. The two forward-facing eyes have overlapping fields of view, which give primates stereoscopic vision. Stereoscopic vision permits accurate perception of distance, which is helpful for handling food or swinging from branch to branch high above the ground. Another distinctive feature of primate skulls, in anthropoids particularly, is the large domed cranium that protects the brain. The inside surface of this dome clearly shows the outline of an unusually large brain - one of the most remarkable characteristics of this group. The shapes of anthropoid brains are different from other mammals: The portion of which the distributive contribution whereby the brain is enwrapped to the visual modalities is especially large, while the compensable portion of attribution to smell is comparatively small.
The primate order includes a handful of species that live entirely on meat (carnivores) and a few that are strict vegetarians (herbivores), but it is composed chiefly of animals that have varied diets (omnivores). The carnivorous primates are the four species of tarsiers, which live in Southeast Asia. Using their long back legs, these pocket-sized nocturnal hunters leap on their prey, pinning it down with their hands and then killing it with their needle-sharp teeth. Tarsiers primarily eat insects but will also eat lizards, bats, and snakes.
Other prosimians, such as galagos and mouse lemurs, also hunt for insects, but they supplement their diet with different kinds of food, including lizards, bird eggs, fruit, and plant sap. This opportunistic approach to feeding is seen in most of monkeys and in chimpanzees. Several species of monkeys, and chimpanzees, but not the other apes, have been known to attack and eat other monkeys. Baboons, the most adept hunters on the ground, often eat meat and sometimes manage to kill small antelope.
Most apes and monkeys eat a range of plant-based foods, but a few specialize in eating leaves. South American howler monkeys and African colobus monkeys eat the leaves of many different trees, but the proboscis monkey on the island of Borneo is more selective, surviving largely on the leaves of mangroves. These leaf-eating monkeys have modified digestive systems, similar to cows, which enable them to break down food that few other monkeys can digest. Other apes and monkeys eat mostly fruit, while some marmosets and lemurs depend on tree gum and sap.
Compared with many other mammals, primates have few young, and their offspring take a long time to develop. The gestational period, the time between conception and birth, is remarkably long compared with other mammals of similar size. A tarsier, for example, gives birth to a single young after a gestational period of nearly six months. By contrast, a similarly sized rodent will often give birth to six or more young after the gestational period lasting just three weeks. Most primates usually give birth to a single baby, although some species, such as dwarf lemurs, usually have twins or triplets.
Once the young are born, the period of parental feeding and protection can be even more drawn out. In small prosimians the young are often weaned after about five weeks, but in apes they are often fed on their mother's milk for three or four years, and they may continue to rely on her protection for six or more years. This long childhood - which reaches its extreme in humans - is a crucial feature of a primate's life because it enables complex patterns of behaviour to be passed on by learning.
Some primates have fixed breeding seasons, but many can breed anytime of the year. In many species, females signal that they are in estrus - receptive and ready to mate - by releasing special scents. In other species, females develop conspicuous swelling around their genitals to signal their readiness for mating. Such swelling is especially noticeable in chimpanzees. While most copulation occurs when the females are receptive, in some species, such as humans and pygmy chimpanzees, copulation frequently occurs even if the female is not in estrus.
Primates display a wide range of mating behaviours. Solitary primates, such as aye-ayes and orangutans, have simple reproductive behaviour. Within the territory that each male control, his imperative territorial rights are in assess of several females live, each with their own territory. The male mates with any females within his territory that are receptive. Other species, such as gibbons, form small family groups consisting of a monogamous pair and they’re young. Gorillas form harems, in which one adult male life with several adult females and they’re young. Among social primates, breeding can be complicated by the presence of many adults. Males may cooperate in defending their troop's territory, but they often fight each other for the chance to mate. In some species, only the dominant male mates with the females in the group. Chimpanzee females mate promiscuously with several adult males, although they usually pair up with one high-ranking male during the final few days of estrus, spending all of their time together and mating together exclusively.
Primates have the most highly developed brains in the animal kingdom, rivalled only by those of dolphins, whales, and possibly elephants. Anthropoid primates in particular are intelligent and inquisitive animals that are quick to learn new patterns of behaviour. This resourcefulness enables them to exploit a wide range of foods and may help them to escape attacks by predators.
Many zoologists believe that primates' large brains initially evolved in response to their tree-dwelling habits and their way of feeding. Anthropoid primates, which have the largest brains, live in a visual world, relying on sight to move about and to find and manipulate food. Unlike smell or hearing, vision generates a large amount of complex sensory information that has to be processed and stored. In primate brains, these operations are carried out by part of the brain called the cerebral cortex, which evolved into such a large structure that the rest of the brain is hidden beneath it. Some unrelated mammals, such as squirrels, also live in trees, but they have less-developed eyesight and much smaller brains.
Increased brainpower has had important effects on the way primates live. It has helped them to move about and find food and enabled them to develop special skills. One of the most remarkable of these is Toolmaking, seen in chimpanzees and, to a far greater extent, in humans. Toolmaking, as opposed to simple tool use, involves a preconceived image of what the finished tool should look like - something that is only possible with an advanced brain.
The intelligence of primates is also evident in their social behaviour. For species that live in groups, daily life involves countless interactions with relatives, allies, and rivals. Mutual cleaning and grooming of the fur, which removes parasites, helps to reinforce relationships, while threats
- sometimes followed by combat - maintain the hierarchy of dominance that permeates typical primate troops.
Primates use a variety of methods to communicate. In solitary prosimians, when animals are not within sight of each other, communication is often accomplished by using scents. Such animals use urine, faeces, or special scent glands to mark territory or to show a readiness to mate. In social anthropoids, visual and vocal signals are much more important. Most monkeys and apes speak with a complex array of facial expressions, some of which are similar to the facial expressions used by humans.
Primates also talk with a repertoire of sounds. These range from the soft clicks and grunts of the colobus to the songs of the gibbon and the roaring of the howler monkey, which can sometimes be heard more than 3 km. (2 mi.) away. Far-carrying calls are used in courtship, both to keep group members from getting separated and to mark and maintain feeding territories. Some primate utterances convey more precise messages, often denoting specific kinds of danger. In the wild, researchers have observed that chimpanzees run through as much as 34 different calls, and evidence suggests that they can pass on information-such as the location of food-using this form of communication.
Comparatively, little in effect is known about the origins of primates compared with many other groups of mammals, because primates have left relatively few fossil remains. The chief reason for the scarcity of fossils is that forests, the primary home for most early primates, do not create good conditions for fossilization. Instead of being buried by sediment, the bodies of early primates were more likely to have been eaten by scavengers and their bones dispersed.
The earliest fossils of primates discovered dates from the end of the Cretaceous Period, about 65 million years ago. These early fossils include specimens of a species called Notharctus, which resembles today's lemurs and had a long pointed snout. The ancestors of another prosimian group, the tarsiers, are known from fossils that date from the early Eocene Epoch, about 50 million years ago. In 1996 researchers in China recovered fossil bones of a primitive primate no bigger than a human thumb. The animal, named Eosimias, existed in as much as 45 million years ago. Many scientists believe that Eosimias is an example of a transitional animal in the evolution of prosimians to anthropoids.
The origin of anthropoids has been difficult to pin down. A single anthropoid fossil has been found that may come from the Eocene Epoch, but conclusive fossil evidence of anthropoids does not appear until the Oligocene Epoch, which began 38 million years ago. These early anthropoids belonged to a lineage that led to the catarrhine primates - the Old World monkeys, apes, and humans. The platyrrhine primates, which include all New World monkeys, are presumed to have diverged from the Old World monkeys during the Eocene Epoch. They evolved in isolation on what was then the island continent of South America. Genetic analysis shows that New World monkeys clearly have the same ancestry with the catarrhines, which means that they must have reached the island continent from the Old World. Exactly how they did this is unclear. One possibility is that they floated across from Africa on logs or rafts of vegetation, journeying across an Atlantic Ocean that was much narrower than it is today.
Of all primate groups, the apes are the direct ancestors of humans that bring on the most provocative of studies. One distinguishing query that finds of its vexation is that of two groups diverging. Based on the comparisons of genes and the structure of body parts, scientists think that the line leading to the orangutan diverged from the one leading to humans about 12 million years ago. The ancestral line leading to chimpanzees did not diverge until more recently, probably between five and seven million years ago. This evidence strongly suggests that chimpanzees are our closest living relatives.
The word primate means "the first.” When it was originally coined more than two centuries ago, it conveyed the widely held idea that primates were superior to all other mammals. This notion has since been discarded, but nonhuman primates still generate great interest because of their humanlike characteristics.
In scientific research, much of this interest has focussed on primate behaviour and its correspondence with human behaviour. Attempts have been made to train chimpanzees and orangutans to mimic human speech, but differences in anatomy make it very difficult for apes to produce recognizable words. A more revealing series of experiments has involved training chimpanzees, and later gorillas, to understand words and to respond using American Sign Language. In the late 1960s, a chimp named Washoe learned more than 130 signs. In the 1970s and 1980s, a gorilla named Koko learned to use more than 500 signs and to recognize an additional 500 signs. One outcome of these long-running experiments was that the chimps or gorillas occasionally produced new combinations of signs, suggesting that the animals were not simply repeating tricks that they had learned. More recently, chimps have been trained to talk with humans by using coloured shapes or computer keyboards. They too have shown an ability to associate abstract symbols with objects and ideas - the underlying basis of language.
Apes and monkeys also play an important role in the field of medical research. Because their body systems work very much like our own, new vaccines and new forms of surgery are sometimes tried on apes and monkeys before they are approved for use on humans. Species that are most often used in this way include chimpanzees, baboons, and rhesus monkeys. This kind of animal experimentation has undoubtedly contributed to human welfare, but the medical use of primates is an increasingly controversial area, particularly when it involves animals captured in the wild.
According to figures published by the World Conservation Union (IUCN), more than 110 species of primates - nearly half the world's total - are currently under threat of extinction. This makes the primates among the most vulnerable animals on earth.
The species most under threats are those affected by deforestation. This has been particularly severe in Madagascar, the only home of the lemurs, and it is also taking place at a rapid rate in Southeast Asia, threatening gibbons and orangutans. The almost total destruction of Brazil's Atlantic rainforest has proved catastrophic for several species, including the lion tamarins, which are found only in this habitat. Primates are also threatened by collection for the pet trade and by hunting. Illegal hunting is the chief threat facing the mountain gorilla, a rare African subspecies that lives in the politically volatile border region straddling Uganda, Rwanda, and the Democratic Republic of the Congo.
In the face of these threats, urgent action is currently underway to protect many of these endangered species. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) currently forbids the export of many primates, although not all countries have chosen to follow this law. More direct methods of species preservation include habitat protection and captive breeding programs. Sometimes - for example, the lion tamarin—these programs have met with considerable success. However, without the preservation of extensive and suitable natural habitats, many primate species are destined for extinction.
Humans as primates, have themselves of a physical and genetic similarities showing that the modern human species, Homo sapiens, has a one and the same close relationship to another group of primate species, the apes. Humans and the so-called great apes (large apes) of Africa - chimpanzees (including bonobos, or so-called pygmy chimpanzees) and gorillas - have the same ancestor that lived sometime between eight million and six million years ago. The earliest humans evolved in Africa, and much of human evolution occurred on that continent. The fossils of early humans who lived between six million and two million years ago come entirely from Africa.
Humans and great apes of Africa have the same ancestor that lived between eight million and five million years ago. Most scientists distinguish among 12 to 19 different species of early humans. Scientists do not all agree, however, about how the species are related or which ones simply died out. Many early human species - probably most of them - left no descendants. Scientists also debate over how to identify and classify particular species of early humans, and about what factors influenced the evolution and extinction of each species.
The tree of Human Evolution Fossil evidence shows that the first humans evolved from ape ancestors at least six million years ago. Many species of humans followed, but only some left descendants on the branch leading to The Homo sapiens. In this slide show, white skulls represent species that lived during the period shown; gray skulls represent extinct human species.
Early humans first migrated out of Africa into Asia probably between two million and 1.7 million years ago. They entered Europe much later, generally within the past one million years. Species of modern humans populated many parts of the world much later. For instance, people first came to Australia probably within the past 60,000 years, and to the Americas within the past 35,000 years. The beginnings of agriculture and the rise of the first civilizations occurred within the past 10,000 years.
The scientific study of human evolution is called Paleoanthropology. Paleoanthropology is a subfield of anthropology, the study of human culture, society, and biology. Paleoanthropologists search for the roots of human physical traits and behaviour. They seek to discover how evolution has shaped the potentials, tendencies, and limitations of all people. For many people, Paleoanthropology is an exciting scientific field because it illuminates the origins of the defining traits of the human species, and the fundamental connections between humans and other living organisms on Earth. Scientists have abundant evidence of human evolution from fossils, artifacts, and genetic studies. However, some people find the concept of human evolution troubling because it can seem to conflict with religious and other traditional beliefs about how people, other living things, and the world developed. Yet many people have come to reconcile such beliefs with the scientific evidence.
Modern and Early Humans have undergone major anatomical changes during evolution. This illustration depicts Australopithecus afarensis, the earliest of the three species, the Homo erectus, an intermediate species, whereby the Homo sapiens, a modern human, and Homo’s ergaster. The modern humans are much taller than A. afarensis and have flatter faces and a considerable brawny brain. Modern humans have a larger brain than H. erectus and almost flat face beneath the front of the braincase.
All species of organisms originate through the process of biological evolution. In this process, new species arise from a series of natural changes. In animals that reproduce sexually, including humans, the term species refers to a conjunctive organization into groups whose adult members regularly interbreed, resulting in fertile offsprings that are, offsprings themselves capable of reproducing. Scientists classify each species with a unique, but two-part scientific names. In this system, modern humans are classified as Homo sapiens.
The mechanism for evolutionary change resides in genes—the basic units of heredity. Genes affect how the body and behaviour of an organism develop during its life. The information contained in genes can change - a process known as mutation. The way particular genes are expressed - how they affect the body or behaviour of an organism - can also change. Over time, genetic change can alter a species’s overall way of life, such as what it eats, how it grows, and where it can live.
Genetic changes can improve the ability of organisms to survive, reproduce, and, in animals, raise offspring. This process is called adaptation. Parents pass adaptive genetic changes to their offspring, and ultimately these changes become common throughout a population - a group of organisms of the same species that share a particular local habitat. Many factors can favour new adaptations, but changes in the environment often play a role. Ancestral human species adapted to new environments as their genes changed, altering their anatomy (physical body structure), physiology (bodily functions, such as digestion), and behaviour. Over long periods, evolution dramatically transformed humans and their ways of life.
Geneticists estimate that the human line began to diverge from that of the African apes between eight million and five million years ago (paleontologists have dated the earliest human fossils to at least six million years ago). This figure comes from comparing differences in the genetic makeup of humans and apes, and then calculating how long it probably took for those differences to develop. Using similar techniques and comparing the genetic variations among human populations around the world, scientists have calculated that all people may share common genetic ancestors that lived sometime between 290,000 and 130,000 years ago.
Humans belong to the scientific order named Primates, a group of more than 230 species of mammals that also includes lemurs, lorises, tarsiers, monkeys, and apes. Modern humans, early humans, and other species of primates all have many similarities plus some important differences. Knowledge of these similarities and differences helps scientists to understand the roots of many human traits, and the significance of each step in human evolution.
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