How fossils show what lived in the past — Science, 7–10 years

A fossil is preserved evidence of ancient life, such as a bone, shell, leaf or footprint. Fossils help us learn about living things and places from long before people kept records.

The idea

When a living thing dies, its remains usually rot or are broken apart. Sometimes mud, sand or ash covers them quickly, and minerals slowly replace or preserve parts of them. The result can be a fossil, including a shape left in rock by a shell, leaf or footprint.

Why it matters

People wanted to know what Earth was like before humans could observe it or write about it. Fossils provide clues instead of guesses: they can show an animal's shape, what it ate, or whether a place was once muddy, dry or under the sea. Scientists compare many clues before drawing conclusions.

A worked example

Imagine finding a three-toed footprint in a slab of rock. First, you record its length, about 24 centimetres, and its shape. Next, you find several similar prints in a line, showing that an animal walked there. Finally, you compare them with known tracks; the rock may once have been soft mud on land.

The common trap

It is easy to think a fossil is simply an old bone, because dinosaur bones are famous examples. But fossils can be impressions, casts, shells, pollen or tracks, and many are from plants or small sea creatures. Also, a fossil does not show every detail of the original living thing.

Where it is used

Fossils are used in museums and field research to reconstruct ancient environments and life. A fossil shell high in a mountain can suggest that the rock formed under water long ago. Fossils also help scientists compare layers of rock and decide which ones formed earlier.

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