Essay on fossils
Nature and mode of preservation:
The varieties in the fossils correspond to what is preserved and how it is preserved. Thus they are of the following nature:
(i) Fossils may comprise the remains of the complete animal but that is very rare. Such fossils chiefly include insects preserved in amber, animals in asphalt, and mammoths and other mammals frozen in ice. But such fossils are of rare occurrence and are of recent origin.
(ii) There may be petrified remains of hard parts of body in rocks. These are often incomplete and are found in broken fragments.
(iii) There may be just the impressions of footprints or leaf- prints and not the original part of the organism.
(iv) Fossils might be also in the form of casts or mould.
Conditions favourable for preservation:
We know that millions of animals and plants had lived, died and were destroyed without leaving a trace. But it has been observed that two factors are favourable for the preservation of organisms as fossils
(a) The possession of hard parts such as shells and bones, and
(b)Quick burials of the remains by different processes to prevent destruction by scavengers and decay.
Any animal or plant satisfying the above two conditions can be preserved as fossils under normal conditions. The condition hi which fossils occur depends on their original composition and on the material in which they are embedded.
Fossilisation may occur in several ways. Sometimes the soft parts