Question

What are fossils? How are they formed? Describe in brief two methods of determining the age of fossils. State any one role of fossils in the study of the process of evolution.
                                     OR
What are fossils? How are they formed? List two methods of determining the age of fossils. Explain in brief the importance of fossils in deciding the evolutionary relationships.

Answer 1

Fossils are dead remains of animals and plants from remote past.
Fossils are formed when dead organisms are not completely decomposed. The organisms may get trapped in resins of tree, lava of volcanoes or hot mud, which when hardens retains the animal's parts thus forming fossils.
Two methods of determining the age of fossils are:
(a) Relative method: By estimating the age of the layer of earth's crust where the fossil is found. Fossils near the surface are recent and those in the deeper layers are more ancient.
(b) Radio-carbon dating method: By detecting the ratios of different isotopes of carbon in the fossils.
Fossils play the following roles:
(i) By determining the age of fossils we come to know the type of earth strata present at that time.
(ii) We can also know the type of animals and plants present on the earth at that time.
(iii) They help in establishing evolutionary relationship by providing connecting links.

Answer 2

Fossils are the preserved traces of the organisms that once existed and now they are extinct. Fossils are formed because some organisms failed to decay completely and have remained preserved till today.

The age of the fossils can be determined by the following way:

1. Radiometric dating :

In this method, the age of the fossil can be determined by tracing the radioactive elements present in the rocks and examining it chemically.

2. Relative dating :

The fossils are found in the sedimentary rocks in the form of layers accumulated over large span of time. So, using this fact, the geologist find the age of fossils in the way that the fossil found at the bottom of those layers are found to be older than that found above those.

• Fossils have a significant role in evolution as they help in creating evolutionary relationships with the earlier organisms and the present day organisms.