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.

(N/A) Fossils are the preserved remains or impressions of prehistoric organisms found in the different strata of the Earth's crust.
Fossils are formed when dead organisms are not completely decomposed. When organisms get trapped in substances like tree resin,volcanic lava,or hot mud,these materials harden over time and preserve the body parts or impressions of the organism.
Two methods of determining the age of fossils:
$(a)$ Relative method: This involves estimating the age of the sedimentary rock layer where the fossil is found. Fossils found in layers closer to the surface are more recent,while those found in deeper layers are more ancient.
$(b)$ Radio-carbon dating method: This involves detecting the ratios of different isotopes of carbon (specifically $C^{14}$) present in the fossil to calculate its age.
Role of fossils in evolution: Fossils provide evidence of evolutionary history and help in identifying connecting links between different groups of organisms,such as $Archaeopteryx$,which acts as a link between reptiles and birds.