Guide to Fossils -Fossilisation



Fossils are abundant in cliffs of Dover. This article is part of our Guide to Fossils.

The life which is preserved in stone and monuments is called fossils. All living organisms could leave fossils, but only the hardest parts of animals or plants can fossilise. The other internal parts which are soft and decomposable cannot be preserved as they decay rapidly. However the skeletons and bones can be fossilised. There is no record of fossils for soft organisms like worms and jellyfish.

Fossils include footprints of animals and fossilized tracks have been found in Johnson farm in St. George Utah. It is also seen that eggs, animal dung and nests with eggs have been preserved in stone.

The formation of fossils occurs in a number of ways and could be formed when an animal or plant dies in a watery environment consequently getting buried in mud and silt. Small bugs and insects can get trapped in tree sap eventually hardening to form amber which is a semiprecious material. Volcanic eruptions too could form fossils when animals get trapped in hot ash flows.


The most common fossils are the remains of shelled invertebrates such as snails, clams and corrals. These by far make the most of the fossil record. Plants could leave fossils too. The fossil record of whole forests could turn out to be coal. However, individual plant structures do not survive as the plant materials get compressed to much smaller than their original size.


Fossils of animals are rarer compared to plants as animals need to become fossilized when animals die in a watery environment getting buried in silt or mud. Therefore, most animals do not get fossilised unless they die close to a lake or stream. There are certain animals which have no fossil records which have been discovered. Thus, there is no trace of how diverse animals could be.

The creation of natural molds occur when hardened sediments form and water percolates through the ground dissolving out the remains, leaving behind a cavity within which only the form is preserved. This is what is called a natural mold. Scientists could form casts out of these when filled with plastic material. In case the molds are filled with mineral matter through subsurface water, natural casts are created. This is how insects are preserved in amber millions of years ago. It is the result of insects enveloping through sticky tree resin which has been hardened to become amber. Detailed microscopic studies could be carried out on the insect’s minute structure.