Why Fossils Form

A fossil is a record of past life. Under most circumstances, there are two requirements before a plant or animal can become a fossil: hard parts and a rapid burial. Shells, bones, and teeth are hard parts that preserve well. But it´s not enough to have hard parts - those bones or teeth, left on the surface of the Earth, decay until nothing is left. However, if a dead animal or plant is buried quickly, for example, if it falls into a deep, muddy swamp or is buried during a sandstorm, there is less opportunity for the parts to decay, and a better chance to form a fossil.