B.A. / B.Sc. (Honours) 4th Semester (Theory)

Transcription

1 Course Name: PREHISTORIC ARCHAEOLOGY Paper No. & Title: B.A. / B.Sc. (Honours) 4th Semester (Theory) Topic No. & Title: (4/17) Geological time scale and Appearance of Man The history of the earth is a very complex and vast subject which deals with the appearance of all the living and non living matter. The formation of rocks, minerals and different geomorphological features besides birth and evolution of simple unicellular microorganism to modern human being are subject matter of the history of the earth. Similarly the formation and development of vegetation from simple lichen like forms to woodland through ages also form an inseparable part of it. The occurrence and development of particular rock strata and corresponding life forms together with associated environment are different events in the history of the earth considered for chronological succession in the event of impossibility of devising a time frame with calendrical accuracy. Thus the geological time scale provides a system of chronological measurement relating stratigraphy to time that is used by geologists, paleontologists and other scientists to describe the timing and relationship between events that have occurred during the history of the Earth. British geologists were responsible for the grouping of periods into Eras and the subdivision of Tertiary and quaternary periods into epoch. William Smith (1915) and Charles Lyell (1930) first recognized that rock strata represented successive time periods, time scales could be estimated only very imprecisely since various kinds of rates of change used in

2 estimation were highly variable. While creationists had been proposing duties of around six or seven thousands years for the age of the Earth based on Bible, early geologists were suggesting millions of years for geologic period with some even suggesting a virtually infinite age for the Earth. Geologists and paleontologists constructed the geologic label based on the relative position of different strata and fossils, and estimated the time scale based on studying rates of various kinds of weathering erosion, sedimentation and lithification. Until the discovery of radioactivity in 1896 and development of its geological application through radiometric dating during the first half of the 20 th the century (pioneered by such geologists as Arthur Holmes) which allowed for more precise absolute dating of rocks, the ages of various rocks starter the age of the Earth were the subject of considerable debate. The first geological time scale was eventually published in 1913 by the British geologist Arthur Holmes. He greatly furthered the newly created discipline of geochronology and published the world renowned book The Age of the Earth in which he estimated the Earth s age to be at least 1.6 billion years. The study of Earth from the beginning of time to the present has been the task of geologists who attempt to unravel the events that have shaped our planet as it is today. The Earth carries the history of geological events in its rock layers. It follows that the oldest layers are at the bottom and the youngest are at the top. With this understanding geologists are able to determine the ages of rock relative to one another. By assembling all these layers together, scientists have worked out what is known as the stratigraphic column or record of the various ages of rocks. The record spans the 4.6 year record of Earth s history. In order to simplify the huge amount of geological information; geologists have broken down Earth s history into sections which are called geological eras, periods and epochs. Fossil records have shown that life existed for about 3,800 million years. Their fossil record allows geologists to date and compare rocks across geological time. For example, dinosaur fossils are only found during the Mesozoic era some million years ago. In 1977 the Global commission of Stratigraphy (now the International commission on Stratigraphy) started an effort to define global reference called Global Boundary Staratotype Sections and Points (GSSP) for geologic periods and faunal stages. On the basis of worldwide data a standard chart has been prepared to understand the geological time scale. This list is divided first into the geologic eras of the Phanerozoic (the Cenozoic, the Mesozoic, and the Paleozoic) and then into the geologic periods of each era. Each period has its own table, in which it is subdivided into epochs and stages. Each stage is assigned an age in mya an acronym for million years ago, which is the age at which it began. Most of these ages are derived from astronomical cycles in sediments, magnetic data, bio-stratigraphic data and radiometric dating methods. The GSSP assigned to each stage is that stage's lower boundary and oldest point. Table 1. Era Period Epoch Pivotal Events Cenozoic Era The Age of Mammals Holocene 10,000 ya to day Human civilization

3 65 m ya through today Quaternary period The Age of Man 1.8 mya to today Tertiary period 65 to 1.8 mya Neogene mya Paleogene mya Pleistocene The last Ice Age mya Pliocene mya Miocene 24-5 mya Oilgocene mya Eocene mya Paleocene mya The first human (Hamo sapiens) evolved. Mammoth, mastodons, saber-toothed cuts, giant ground sloths and other pleistocene mega fauna First Hominids (Australo pithecines) Modern form of whale More mammals, including the horses, dogs and bears, modern birds, south American monkey apes in southern Europe. Ramapithecus Starts with a minor extinction (36 mya) many new mammals (pigs, deer, eats, rhinos etc.) Mammals abound, Rodents appear, primitive whale appear First large mammals and primitive primate, plesiadaptiformsc * mya = million years ago Recent human activity, including stunning population growth, sprawling megacities, increased use of fossil fuels, global climate change and sharp increase in plant and animal extinctions have changed the planet to such an extent that we are entering what they called the Anthropocene (New Man) Epoch. The world wide geological community is formally considering whether the Anthropocene should join other more familiar units on the Geological time scale. The Anthropocene represents a new phase in the history of both human kind and of the Earth, when natural forces and human forces became intertwined, so that the fate of one determines the fate of the other. Geologically, this is a remarkable episode in the history of this planet. Start date of the new Epoch may be considered to have started in the late 18 th century when the activities of human first began to have a significant global impact on the Earth s climate and ecosystems (commercialization of the steam engine), others link it to earlier events, such as the rise of agriculture. An epoch is a division of the geological timescale. Epochs are sub-divisions of periods and are themselves subdivided into ages. The time span of an epoch can differ but is usually between 50 and 5 million years. The youngest epochs of the geologic time scale are even shorter,

4 the Pliocene and Pleistocene epochs lasted less than 3 million years and the Holocene epoch last only 10,000 years (Table 1). The earliest ancestors of humans were members of the genus Australopithecus who were intermediate between apes and people. Both Australopithecines and humans are biologically similar enough to be classified as members of the same biological tribe-the Hominini. All people, past and present along with the australopithecines are hominin. We share in common not only the fact that we evolved from the same ape ancestors in Africa but that both genera are habitually bipedal or two footed, upright walkers. By comparison, chimpanzees, bonobos and gorillas are primarily quadrupedal or four footed. Over the last decade, there have been a number of important fossils discoveries in Africa of what may be very early transitional ape hominin or proto hominin. These creatures lived just after the divergence from our common hominid ancestor with Chimpanzees and bonobos, during the late Miocene and early Pliocene Epochs. The fossils have been tentatively classified as members of three distinct genera Sahelanthropus, Orrorin and Ardipithecus. Sahelanthropus was the earliest, dating 7-6 million years ago. Orrorin lived about 6 million years ago, while Ardipithecus remains have been dated to million years ago. At present, the vote is still out as to whether any of these three primates were in fact true hominin and if they were our ancestor. The classification of Sahelanthropus has been the most in question. The earliest australopithecines very likely did not evolve until 5 million years ago or shortly thereafter (during the beginning of the Pliocene Epoch) in East Africa. The primate fossil record for this crucial transitional period leading to australopithecines is still scanty and somewhat consuming. However, by about 4.2 million years ago, unquestionable australopithecines were present. By 3 million years ago, they were common in both East and South Africa. Same have been found dating to this period in North Central Africa also. As the Australopitecines evolved, they exploited more types of environments. Their early proto hominin ancestors had been predominantly tropical forest animals. However, African forests were progressively giving way to sparse woodlands and dry grasslands or savannas. The australopithecines took advantage of these new conditions. In the more open environments, bipedalism would very likely have been an advantage. By 2.5 million years ago, there were at least 2 evolutionary lines of hominin descended from the early australopithecines. One line apparently was adapted primarily to the food resources in lake margin grassland environments and had omnivorous diet that increasingly included meat. Among them were our early human ancestors who started to make stone tools by this time. The other line seems to have lived more in mixed grassland and woodland environments, like the earlier australopithecines, and was primarily vegetarian. This second, more conservative line of early hominin died out by 1 million years ago or shortly before then. It is likely that all of the early hominin, including humans supplemented their diets with protein and fat rich termites just as some chimpanzees do today. The evolutionary surge that led to Homo Habilis began towards the end of the Pliocene Epoch around 2.5 million years ago when climates were becoming cooler and drier. The evolution of Homo erectus and later species of humans occurred during the Pleistocene Epoch

5 (18,00,000-10,000years ago). The Pleistocene was generally a time of more extreme world cooling and recurrent glaciations (ice age). Scientific evidences indicate that humans evolved into their present form during the Pleistocene. In the beginning of the Pleistocene Paranthropus species are still present as well as early human ancestors but during the lower Paleolithic they disappeared and the only hominid species found in fossil record is Homo erectus for much of the Pleistocene. The middle and late Paleolithic show the appearance of new types of humans as well as the development of more elaborate tools than found in previous eras. According to mitochondrial timing techniques, modern humans migrated from Africa after the Riss glaciations in the middle Paleolithic during the Eamian stage, spreading all over the ice-free world during the late Pleistocene. Homo erectus moved from scavenging to hunting, developing the hunting gathering life style that would remain dominant throughout the Paleolithic into the Mesolithic. The unlocking of the new niche of hunting gathering subsistence drove a number of further changes, behavioural and physiological leading to the appearance of Homo Heidelbergensis by some 6,00,000 years ago. Homo erectus migrated out of Africa and dispersed throughout Eurasia. Stone tools in Malaysia have been dated to be 1.83 million years old. The Peking man fossil discovered in 1929 is roughly 70,000 years old. In Europe, the Oldowan tradition (known in Europe as Abbevillian) split into two parallel traditions, the Clactonian, a flake tradition and the Acheulean, a hand axe tradition. The Levallois technique for knapping flint developed during this time. The Carrier species from Africa to Europe undoubtedly was Homo erectus. This type of human is more clearly linked to the flake tradition, which spread across southern Europe through the Balkans to appear relatively densely in South East Asia. Many Mousterian finds in the middle Paleolithic have been knapped using a Levallois technique, suggesting that Neanderthals evolved from Homo erectus. Due to lack of written record from this time middle Paleolithic, nearly all of our knowledge of Paleolithic human culture and way of life comes from archaeology and ethnographic comparisons to modern hunter gatherer cultures such as the Kung san who live similarly to their Paleolithic predecessors. The economy of typical Paleolithic society was a hunter gatherer economy. Humans hunted wild animals for meat and gathered food, firewood, and materials, for their tools, clothes or shelters. At the end of Paleolithic, specifically the Middle and or Upper Paleolithic, humans began to produce works of art such as cave paintings, rock art and jewellery and began to engage in religious behavior such as burial and ritual. Palaeolithic groups such as the Neanderthals who had a middle Paleolithic level of technology appear to have hunted large game just as well as upper Paleolithic modern humans and the Neanderthals in particular may have likewise hunted with projectile weapons. Neanderthal use of projectile weapon in hunting occurred very rarely and the Neanderthal hunted large game animals mostly by ambushing them and attacking them with Melee weapons such as thrusting spears rather than attacking them from a distance with projectile weapons. According to Bischoff and others (2003) the first proto Neanderthal traits appeared in Europe as early as 600, ,000 years ago. Several cultural assemblages have been linked to the Neanderthals in Europe. The earliest, the Mousterian stone tool culture, dates to about 300,000 years ago. Later Mousterian culture is also seen in Asia and in Africa dated after

6 150,000 years ago at the Jebel Irhoud site located 620 km south of Gibraltar. Late Mousterian artifacts were found in Gorham s cave on the remote south facing coast of Gibraltar. Other tool cultures associated with Neanderthal include Aurignacian, Gravettian developed with gradual continuity not distributed by population change. Early Neanderthal lived in Last glacial age for a span of about 100,000 years. Because of the damaging effects the glacial period had on the Neanderthal sites, not much is known about the early species. Countries where their remains are known include most of Europe south of the line of glaciations, roughly along the 50 th parallel north, including most of Western Europe, including the south coast of Great Britain, Central Europe and Balkans. Some sites are also reported from Ukraine and in Western Russia and East of Europe in Siberia to the Atlantic Mountains and southwest Asia upto the Indus River. The Neanderthals disappeared from the fossil record after about 25,000 years ago. The last traces of Mousterian culture (without human specimens) have been found in Gorham s cave on the remote south facing coast of Gibraltar dated 30,000 to 24,000 years ago. The Possible causes of extinction as evident from the discussion of scholars like Diamond (2009), Robin (1992) etc. are 1. Neanderthals were a separate species from modern humans and became extinct (due to climate change or interaction with humans) and were replaced by Homo sapiens moving into its habital beginning about 80,000 years ago. Competition from Homo sapiens probably contributed to Neanderthal extinction. 2. Neanderthals were a contemporary subspecies that bred with Homo sapiens and disappeared through absorption. 3. A campanian ignimbrite volcanic super-eruption around 40,000 years ago followed by a second one a few thousand years later, has been hypothesized as having contributed to the demise of Neanderthal based on evidence from Mezmaiskaya cave in the Caucasus Mountains of Southern Russia. There is a longer certainty regarding the identity of the human who produced the Aurignacian culture, even though the presumed westward spread of anatomically modern humans across Europe is still based on the controversial first dates of the Aurignacian. Currently the oldest Europe anatomically modern Homo sapiens is represented by a robust modern human mandible discovered at Pestera cu Oase (South west Romania) dated to 34,000 36,000 years ago. Human skeletal remains from the German site of Vogelherd, so far regarded as the best association between anatomically modern Homo sapiens and Aurignacian culture, were revealed to represent intrusive Neolithic burials into the Aurignacian levels and subsequently all the key Vogelherd fossils are now dated to 3,900 5,000 years ago instead. Homo sapiens are the only living species in the Homo genus. Anatomically modern human originated in Africa about 20,000 years ago, reaching full behavioural modernity around 50,000 years ago. Anatomically modern humans evolved from archaic Homo sapiens in Africa in

7 the middle Paleolithic about 200,000 years ago. By the beginning of Upper Paleolithic period full behavioural modernity, including language, music and other cultural universals had developed. Conclusion: The term human in the context of human evolution refers to the genus Homo, but studies of human evolution usually include other hominids, such as Australopithecines, from which the genus Homo diverged by about 2.3 to 2.4 million years ago in Africa. Scientists have estimated that human branched off from their common ancestors with chimpanzees about 5-7 million years ago. Several species and subspecies of Homo evolved and are now extinct. Examples include Homo erectus, Neanderthals, Archaic Homo sapiens, the forerunner of anatomically modern humans evolved between 400,000 and 250,000 years ago. With the help of geological time scale the various stages of human species can be studied properly.