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. A footprint forms when an animal steps into soft mud. There are two kinds of fossils: body fossils and trace fossils. Footprints and feather or skin prints can be trace fossils.
Most animals and plants that die rot away. They 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. It 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. Rock that formed under the sea can end up in mountains. Sea animal fossils are found at the top of Mount Everest.
Animals got stuck in the sticky asphalt at the La Brea Tar Pits. Hunters that came to eat them got stuck too. The animals were stuck in the asphalt tens of thousands of years ago, during the Ice Age. Saber-toothed cats are among the most common fossils at La Brea in Los Angeles.
Tiktaalik was a fish with a flat head like a crocodile. Tiktaalik fossils are about 375 million years old. Tiktaalik had lobed fins that it may have used to move around on the shore.
Whales once walked on four legs. Pakicetus was an early whale that lived on land.
Words to know
- silt: fine mud
- minerals: rock bits
- asphalt: sticky tar
The short version
Fossils are what is left of plants and animals from long ago. Fossils are found in rock. 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.
Quick facts
- Fossils are found in rock.
- Bones can become fossils.
- 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.
- Tiktaalik fossils are about 375 million years old.
How do fossils form?
A dead animal or plant has to be covered up fast. 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.
Do all animals become fossils?
No. Most animals and plants that die rot away and do not become fossils. Hard parts such as bones, teeth and shells become fossils more often than soft parts.
