What Is a Fossil?

A fossil is a part of an animal or plant that has been preserved in rock. A few living things have been trapped in ice or tar or sticky sap from trees called amber, but most fossils were formed in wet mud and sand. We call that mud and sand “sediment.” As the sediment dries, the trapped, once-living thing becomes part of the rock layers of the earth.

Fossil Butte, National Monument, Wyoming, USA