The organisms that are now fossils were alive when the rocks were being formed. They were buried and preserved as the layers of rock piled up. By studying fossils, paleontologists learn what kind of life existed in various periods of the earth's history. The fossil record shows a gradual increase in the complexity of animals and plants. This gradual change in body form is called evolution.
Paleontology is important in the study of geology.
The age of rocks may be determined by the fossils in them. Fossils also tell whether rocks were formed under the ocean or on land. Most rocks that contain marine shell fossils were formed under the ocean. Most rocks that contain land animal and land plant fossils were formed on land. The knowledge of where rocks were formed helps scientists map the world as it was millions of years ago.