Science
What are fossils and how are they made?
Quick answer
Fossils are the preserved remains or traces of plants and animals that lived long ago, usually found in sedimentary rock. They help scientists learn how life on Earth has changed.
In one sentence
A fossil is the remains or trace of a living thing from long ago that has been preserved in rock.
Explained
Most living things rot away after they die. But very occasionally, a plant or animal is buried quickly in mud or sand, which protects it. That is the start of a fossil.
Here's how a typical fossil forms:
- A sea creature dies and sinks to the seabed.
- The soft parts rot away, leaving hard parts like shells, bones or teeth.
- Layers of sediment pile on top, burying the remains deeper and deeper.
- Over millions of years, the layers harden into sedimentary rock. Minerals in water seep into the bones or shell and slowly replace them, turning them to stone.
- Much later, movements of the Earth lift the rock up, and wind, rain or waves wear it away until the fossil appears.
Think of it like pressing a shell into play dough, then letting the dough set hard. The shape is kept, even if the shell is gone.
Not all fossils are bones. Trace fossils show what animals did: footprints, burrows, nests and even fossilised poo, called coprolites. Insects have been preserved in amber, which is fossilised tree resin.
Fossils are one of the main kinds of evidence for evolution. Older rock layers usually lie deeper, so scientists can see how living things changed over time. The oldest fossils, made by tiny microbes, are more than 3 billion years old.
Examples
- Ammonites, coiled sea creatures, common on some beaches.
- Dinosaur bones and footprints.
- Shark teeth, often found because teeth are very hard.
- Fern leaves pressed into coal or shale.
- Insects trapped in amber.
shell
rock
leaf
Common mistakes
- "Humans and dinosaurs lived at the same time." Most dinosaurs died out about 66 million years ago, long before the first humans. Birds, though, are living dinosaurs.
- "Fossils are just old bones." They are usually rock that has replaced the bone, and they include footprints, leaves and shells.
- "Every animal that ever lived became a fossil." Fossils are rare. Most living things rot or are eaten before they can be preserved.
Quick quiz
Fossils
Check what you know with 4 quick questions.
Question 1 of 4
In which type of rock are most fossils found?
Practise it
Try it
Press a shell or leaf into clay to make a mould, then fill it with plaster for a "cast" fossil. For a story, try The Sea in the Desert.
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For grown-ups
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