Fossils are the geological remains of impressions or traces of organisms that existed in the past. They were preserved in the rocks of earth. Their structure and nature give an idea of organic evolution such as:
1. How the organisms have gradually evolved from their ancestors.
2. The time of evolution of organisms.
3. They give an idea of gradual evolution of a given animal from a primitive stock. E.g., Modern horse from Hyracotherium.