Fossils are the remains of animals and plants left in the earth before people lived in the world.
They are most often found in rocks that were once soil that has hardened and become rock over time. The earth is very old. It has been here for a much longer time than people have lived on it. Therefore, we have no record written down by people of what the world was like in those long ago times. Paleontologists study the evidence contained in the earth as fossils in order to know what it was like then.