Fossils tell of past life — Earth science, 7–10 years
A fossil is a trace or remains of living things preserved in rock. Fossils let us investigate life that existed long before people.
What a fossil is
A fossil can be a bone, shell, tooth, footprint or even a tunnel left in old sediment. Usually, the soft parts disappear and minerals slowly fill or replace the hard parts. The rock keeps a clue about a living thing that existed long ago.
Why fossils matter
Scientists needed evidence to learn about creatures and environments that no person had seen alive. Fossils solve this problem by preserving clues in layers of rock. A shell high in a mountain can also show that the area was once under the sea.
Reading a fossil clue
A rock contains a three-toed footprint. Step 1: scientists measure it, perhaps 24 centimetres long. Step 2: they compare its shape with footprints made by known animals. Step 3: if the rock layer is 120 million years old, they infer that a three-toed animal walked there then. The print is evidence, not a perfect photograph.
The common mix-up
It is easy to think every old bone is a fossil, because both are hard and may lie in the ground. A fossil has been preserved by natural processes, often inside rock, over a very long time. A recent bone can still be a normal bone even if it is dirty, dry or buried.
Fossils outside school
Palaeontologists use fossils to reconstruct ancient animals, plants and habitats. Museum displays, natural-history documentaries and some discoveries at building sites all depend on this evidence. Fossils can also help scientists compare rock layers in different places, but they do not answer every question alone.
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