What Are Fossils?

A fossil is the preserved remains or trace of a living thing from long, long ago. Fossils can be bones, teeth, shells, or even footprints left in rock! They are like clues that tell us what ancient animals and plants looked like. The oldest fossils are billions of years old! Fossils are usually found in sedimentary rocks — rocks made from layers of sand and mud that piled up over millions of years.