Fossils

A fossil is the preserved evidence of an ancient organism. Some fossils are formed from body parts such as bones or shells. Other fossils, such as footprints or burrows, are formed from traces of an organism's activities.

Fossils are typically found in sedimentary rocks. Sedimentary rocks usually form in layers. Over time, new layers are added on top of old layers in a series called a rock sequence.

The layers in an undisturbed rock sequence are in the same order as when they formed. So, the deeper layers are older than the shallower layers.The relative ages of fossils can be determined from their positions in an undisturbed rock sequence. Older fossils are usually in deeper layers, and younger fossils are usually in shallower layers.

The way an organism looks or acts is called a trait.

Scientists use fossils to learn more about the traits of ancient organisms.

Fossils can preserve the remains of body parts and activities. A fossil of a body part, such as a tail or a wing, can tell you what an organism looked like. A fossil of an organism's activities, such as a burrow or a footprint, can tell you about the organism's behavior.

An organism's fossil may not show all of the organism's traits. This is because most body parts are destroyed during fossil formation. When an organism's body turns into a fossil, only a few body parts are usually preserved.