A fossil is the preserved remains or traces of a living thing from a long time ago.

Most fossils form when living things die and are buried by sediment that hardens into rock over time.

The oldest layer can be found in the bottom layer of rock.

Bone is the animal part that is most likely to form a fossil.

Bones and teeth remain because they are hard and do not decay easily.

A trace fossil shows evidence of the activities of ancient organisms, like footprints.

Sediment is small pieces of rock, soil, and other materials that can bury living things.

A mold fossil is a hollow impression left in rock by a living thing.

A cast fossil is a solid copy of the shape of a living thing.

A carbon film fossil is a thin layer of carbon left behind from a living thing.