Write a note on fossil evidence of evolution



Branch of science that deals with fossils is called palaeontology. Fossils are remnants of plants and animals or their parts and impressions in the form of rocks in the crust of earth. The fossils were formed in the long past when earth containing organisms was covered with rocks. The process of formation of fossils is called fossillisation or petrification.

The fossils formed at different geological times were buried in the sedimentary rocks deposited during that period. The organic materials were gradually converted into inorganic compound and ultimately changed into rocks. The earliest fossil discovered was formed 900 million years ago. They were fossils of uninucleate plants and animals.

The following is a list of different fossils and the time when they were formed.

Man - 1 million years

Bird -  150-200 million years

Mammals - 180-150 million years

Reptiles -  300-150 million years

Amphibians - 350-300 million years

Invertebrates – 460 million years

Protozoa – 900 million years

The palaeontology provides us the opportunity to enjoy the flashback scenes of the life drama that was staged on the earth in the past. Fossils of certain transitional groups relate descendants with their ancestors in a nice way. For example, fossils of Archaeopteryx and Archaeornis preserved their dual characteristics of reptiles and birds. This proved that evolution of birds have occurred from the reptiles through the Archaeopteryx stage.

From the study of fossils the following ideas are conceived:

(i) The animals and plants were changing from time to time.

(ii) Earliest organisms were the simplest forms.

(iii) Gradual complexities occurred progressively in the successive geological periods.

(iv) Occurrence of fossils of transitional forms tells about stepwise progress of evolution.

Basing on fossil records the evolutionary history of camel, horse, elephants, man, etc. have been fully unfolded.

For example, the fossil horse of Eocene, the Eohippus gave rise to Mesohippus of Oligocene.

From Mesohippus, Merychippus descended in Miocene. It had its descendent Pliohippus in Pliocene which was the ancestor of modern horse Equus.

Thus fossils are the direct proof of evolution. But unfortunately neither all the fossils have been excavated nor have all the past forms been fossilized.