Among all the planets, nature has chosen to bestow gift of life on the Earth only. This life is in the highly diversified form consisting of animals and plants thronging land, water and air. It is interesting to learn how the life originated, what kind of it existed in the past and how it evolved through ages. Fossils, which are the remains of prehistoric animals and plants preserved by being buried in earth and hardened like rock, provide the basic information for recasting the past. Based on their study, it has become possible to build up the palaeoenvironment and palaeoclimate and know about the great environmental catastrophes, and understand the processes of evolution.
BEGINNING OF LIFE:
The Earth originated about 4600 million years ago. For the initial about 1100 million years, there was no life (Azoic Eon). Probably in the primordial oceans, life originated about 3500 million years ago in the form of primary protoplasm (pre¬served as a chemical fossil) in the Archaeozoic Eon.
In India the oldest fossil is known from 3200 million year old rocks of Orissa.
THE PROTEROZOIC:
During the Proterozoic Era covering the period from 2500 to 545 million years ago, life was in the form of simple vegetal and unicellular forms like algae, fungi and bacteria. Towards the end of this Era, multicellular plant life and probably some invertebrates appeared.
Ediacaran assemblages from the Bhander Group, Vindhyans of Madhya Pradesh
Stromatolites generated by algal activity during Proterozoic (Gangolihat, Uttar Pradesh)
THE PALAEOZOIC:
With the beginning of the Palaeozoic Era, 545 million years ago, life emerged with great force. Several kinds of multicellular animals with organised body structure originated and proliferated all through this Era extending from 545 to 248 million years from the present. Most of the invertebrate groups like mollusks, brachiopods, etc. originated during this period. Among the vertebrates, fishes came first about 500 million years ago. Land plants originated about 400 to 415 million years ago. At about the same time amphibians originated from fishes. Reptiles also originated about 350 million years ago from amphibians. The period between 355 and 250 million years from the present is characterised by proliferation in the variety and number of plants especially gymnosperms which thrived on marshy lands. These plants gave rise to the coal deposits in India and other countries in Southern Hemisphere.
Scenario depicting Permian (210-250 million year old) Coal-forming vegetation
Coal seam overlain by sandstone in Barakar Formation, Madalia nala section, west central part of Talcher Coalfield, Orissa
THE MESOZOIC:
During the Mesozoic Era (248 to 65 million years ago) several noteworthy changes took place. Many life forms became extinct. Several kinds of land reptiles and conifers evolved in the beginning of this Era. In the seas, several kinds of molluscs (especially ammonites) proliferated. Birds, early mammals, sev¬eral kinds of insects originated during this period. Dinosaurs having originated about 225 million years ago became very large attaining maximum length exceeding 30 metres. In India, dinosaur fossils have been found in peninsular region and these enjoyed their heyday between 70 and 65 million years ago.
A large heteromorphic ammonite - Mariella bergeri, Albian, Maruvattur, Tamil Nadu
Jurassic dinosaur bone bed, Adilabad district, Andhra Pradesh
Earliest bird, Archaeopteryx, originated about 180 mil¬lion years ago from reptiles. Before the end of the Mesozoic Era, angiosperms (flowering plants) and primates also appeared.
A composite skeleton of a dinosaur Kotasaurus yamanpalliensis Yadagiri installed in the Birla Science Centre, Hyderabad (collected near Yamanpalli village, Adilabad district, Andhra Pradesh)
Model of Indian dinosaur installed at GSI, Lucknow
Skull of a Rhynchosaur discovered in the Triassic rocks of the Pranhita-Godavari Valley.
An articulated skeleton of a Rhynchosaur discovered in the Triassic rocks of the Pranhita-Godavari Valley.
Angiospermous fossil flower from Barog, Solan Dist. (H.P.); actual size 5.5 mm, Kasauli Formation; GSI Type No. 20658
THE CENOZOIC:
The end of the Mesozoic Era witnessed the ex¬tinction of several animals, especially dinosaurs, ammonites (a kind of coiled mollusc), some types of corals, etc. due to unfavourable climatic conditions. The Cenozoic Era (65 million years ago to the present), as a result of prolific development of angiosperms coupled with changing environments, was marked by the evolution of various kinds of land mammals and birds. Several slow but important changes occurred during the Cenozoic Era. Reptiles, which ruled the earth during the Mesozoic Era, became less important and their place was taken over by mammals. The seas got dominated by bony fishes (teleosts) and cartileginous fishes (sharks). Several kinds of gastropods, lamellibranchs, echinoderms, etc. lived in the sea. So was the case with the foraminifers (protozoans). It is largely these foraminifers, which on decomposition, gave rise to oil - a source for petrol, diesel, etc. A rich mammalian fauna comprising elephants, horses, deer, camels, rhinoceroses, hippopotamids, bovids, carnivorous animals and sea mammals (sea cows, whales, etc.) originated and developed during the Cenozoic Era.
Foraminifers (highly magnified) useful in oil exploration
Evolution of Elephants & Horses
Skull and mandible of Hexaprotodon sivalensis (an extinct hippoptamid) from Toka near Talokpur, dist. Sirmaur (H.P.) Saketi Formation (Upper Siwalik) GSI Type No. 20894 (SFP/56)
Siwalik hills in northwestern India have provided one of the richest collections of vertebrate fossils (mainly mammals) in the world; these fossils range in age from 18 to 1 million years from the present.
Palate of Stegodon elephantoides with second molar on each side from Siwalik Fossil Park, Saketi, distt. Sirmaur (H.P.) Saketi Formation (Upper Siwalik) GSI Type No.21072 (SFP/46)
It is interesting to note that the Himalayan rocks which presently occupy majestic heights, sometimes even over 8000 metres, were deposited in the sea as clearly indicated by the presence of marine fossils entombed in these rocks.
Evolution of Man:
The incoming of primates including hominids and their evolution giving rise to modern man was the most interesting biotic event during the Cenozoic Era. Early ancestors of man were ape-like non-human primates. Among the earliest pri¬mates akin to hominids, was Ramapithecus, whose fossils have been found in 12 million year old rocks of Siwalik hills in India. These probably walked on their two feet for a while. However, the first definite member of human lineage known as Australopithecus appeared about 4 million years ago; these were ape-faced pre-humans who could stand erect, walk on two hind limbs and were probably the first stone tool users. Earliest human (Homo habilis) appeared about 2 million (20 lakh) years ago in Africa. In the initial stages probably, he did not look like a human. Gradually, he used tools, started living in caves, hunted animals, lived in settlements and finally became the man of the modern age.
In India the oldest fossil man (Homo erectus) has been recovered from the rocks in Narmada Valley (M.P.) which are around 0.7 million (7 lakh) years old.
The broken skull specimen of Homo erectus, first & only of its kind in India, was discovered on 5th December, 1982 in the middle of the Narmada valley in Hathnora, Madhya Pradesh.
Important stages in Evolution of man
Palaeolithic tools
Prepared by Palaeontology Division,GSI, Northern Region, Lucknow
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