In order for fossils to form, there must be a way to preserve the dead remains of animals and plants for a time so that they do not decay completely. The most common way that this occurs is on the bottom of bodies of water. When an animal of plant dies and falls into the water, the remains are sometimes covered up quickly by sediments. The layers of sediment form a protective covering to slow the process of decay.
Over thousands of years, the sediments around the remains harden into rock. The dead animal or plant remains eventually decay leaving an empty space inside the sedimentary rock. Minerals filter down into this space and harden into rock forming a shape just like the animal or plant. This process is called fossilization. The mineral remains are called fossils.
Sometimes there are no minerals that filter down into the empty space in the rock. The space that is left is called an imprint. Some common fossil imprints are dinosaur tracks which are formed when the large animals left their tracks on the bottom of shallow seas or rivers.
There are other ways that fossils can be preserved. Many animals have been found preserved in ice in Siberia. Other fossils, especially Insects, are found imbedded in amber(a sticky sap from trees that covers the insects and then hardens).
