Fossils- the printed stones

When animals and plants die, their bodies may fall into sediments. Usually, they just decay. But sometimes they can become part of sedimentary rocks.

As the rock layers build up, the rock becomes solid. The minerals in the rock may replace the minerals in parts of the dead bodies. This takes place over millions of years.

These remains of living organisms that have changed to rock are called fossils.

Fossils can also be made when an animal leaves an imprint of its footprints or burrow in wet sand or mud.

When more sediment is deposited on top of the imprint and the rock hardens, there may be a mark in the rock.

Clues from fossils

A dinosaur footprint from Arizona USA.

Fossils can help us to work out how a rock formed. Limestone contains fossils from sea animals and plants.

This limestone contains fossils of delicate sea animals called crinoids.

So we know limestone was formed under the sea. Coal sometimes contain fossils of plants that look like ferns. So we know that coal was not formed under the sea.

Coal was formed when trees and other plants fell into swamps millions of years ago.

Fossils tell us about the plants and animals that lived millions of years ago. Some of them were very similar to those found today.

This tells us that those types of plants and animals have been on Earth for millions of years. But other fossils show us strange organisms that do not live on Earth today.