What Are Fossils?

Fossils are indeed the evidence or remains of a living thing, such as a burrow, shell print in a rock, or a bone. As animals and plants long ago were buried after they died (in a sandstorm, sinking in mud, and so on), they gradually were covered by more and more sediment. The harder parts of the organisms, like teeth and bones, became encased in the sediment, and minerals replaced the chemicals in those hard parts over time to form fossils.