Fossils and deep time — Earth science, 11–13 years
A fossil is evidence of ancient life or its activity preserved in rock. Fossils and the layers around them help scientists reconstruct environments and understand that Earth’s history stretches far beyond human lifetimes.
Life leaves traces
Fossils can be bones, shells, leaf shapes, footprints or burrows, not only complete bodies. Usually, quick burial protects a trace from being destroyed, and minerals may replace or fill it over time. The rock then keeps a clue about a living thing and its surroundings.
Why do fossils matter?
The present landscape does not show every place where life once lived. Fossils solve the problem of incomplete memory: they provide physical evidence that can be compared between rocks and regions. They reveal vanished species, ancient climates and changes that took millions of years.
Using rock layers
A fossil shell is found in a lower layer, and a similar shell is found in a higher layer. If the layers have not been overturned, the lower one formed first, so that shell is older than the one above it. If scientists know the species lived for a particular period, the fossil helps match the ages of distant rocks.
A fossil is not a whole history
It is tempting to treat one fossil as a complete picture of the past, because it feels like direct evidence. But fossilisation is rare, and many environments preserve some organisms better than others. Scientists compare many fossils, rock layers and other clues before making a careful conclusion.
Reading ancient environments
Fossils help scientists decide whether a rock formed in a shallow sea, a lake, a forest or a desert. They are also used to locate useful rock layers and to understand how life responds to changing environments. Museums and field researchers use them to test stories about Earth’s past.
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