Fossils are what is left of plants and animals from long ago. Fossils are found in rock. Bones can become fossils. Shells and leaves can become fossils too. There are two kinds of fossils: body fossils and trace fossils. Footprints and feather or skin prints can be trace fossils. Fossils tell us which plants and animals lived long ago. We know dinosaurs lived because we find their fossils.

Most animals and plants that die rot away and do not become fossils. To become a fossil, a dead animal or plant has to be covered up fast. A dead animal is often buried by mud, sand or silt before it rots away. Hard parts such as bones, teeth and shells become fossils more often than soft parts. Water full of minerals seeps into buried bones and teeth and slowly turns them to stone.

Making a fossil takes a very long time, often thousands to millions of years. Layers of mud and sand pile up and slowly turn into rock. In a stack of rock layers, the layers at the bottom are older than the layers on top. Scientists can use radioactive atoms in rock like a clock to work out how old the rock is.

Tiktaalik was a fish with a flat head like a crocodile. Tiktaalik fossils are about 375 million years old. It had lobed fins that it may have used to move around on the shore. Tiktaalik was found in the Arctic, in Nunavut, Canada. Whales once walked on four legs. Ambulocetus was an early whale with big paddle-like feet that used its tail to swim.

Archaeopteryx lived in the Late Jurassic Period, and its fossils were found in limestone in Germany. Archaeopteryx had broad feathered wings and a wishbone, like a modern bird.

Fossils can show how animals lived, not only what they looked like. Trace fossils, such as tracks, tell us about what an animal did.

As of November 2026, the oldest known fossils are about 3.5 billion years old and come from tiny living things in the sea in Australia.

Words to know

• silt: fine mud
• minerals: rock bits
• limestone: kind of rock
• wishbone: forked bone