Question

What are fossils? How are fossils formed and how is their age determined? State the importance of fossils in the study of evolution.

Answer 1

Fossils are the dead remains of plants and animals that are embedded in sedimentary rocks, preserved and petrified.
When a plant or an animal dies, its remains fall on the ground. Over a period of time, its body gets covered by sediments brought by rivers, winds, etc. These sediments keep on getting accumulated for over hundreds of years and when that land gets eroded, the fossils can be seen clearly. Thus, the process of accumulation of dead remains of plants and animals for over hundreds of years results in the formation of fossils.

The age of fossils can be determined by the following ways:
(i) Radiometric dating: In this method, the age of fossils can be determined by tracing the radioactive elements present in the rocks and by examining them chemically.
(ii) Relative dating: Fossils are found in sedimentary rocks in the form of layers accumulated over a large span of time. Considering the fact that fossils found in the bottom layers are older than those found in the layers above them, geologists find the age of the fossils.

Fossils play an important role in tracing evolutionary relationships. They can help in finding the connecting links between different organisms. Also, the depth at which fossils are found tells us their age and the period in which they existed. Fossils found closer to the surface of the Earth are more recent than those present in the deeper layers.