Fossils
Fossils all over the world are usually formed when animails die and get layered by sand or mud. When people find them they are usually 50-150 years old, you can tell what animail it is if you look closely at the bones.
Fossil Fuels
Fossil fuels are substances made deep within the earths surface from the remains of animals and plants. Over time they heat up and pressure turns constantly. Fossil fuels are sometimes part of fossils.