How Fossils Form

Fossils are the remains or traces of ancient living things preserved in rock. They tell us about life millions of years ago. Without fossils, we would not know dinosaurs ever existed! Most fossils take thousands or millions of years to form.

How It Happens

When an animal dies, its soft parts usually decay quickly. But sometimes the hard parts, like bones and teeth, get buried in mud or sand. Over millions of years, minerals slowly replace the bone. The bone turns to stone, creating a fossil. This process is called permineralization.

Types of Fossils

There are many types of fossils. Body fossils preserve bones, teeth, or shells. Trace fossils preserve footprints, nests, or burrows. Some fossils are just imprints of leaves or feathers in rock. In rare cases, whole animals are preserved in amber, tar, or ice.

Fun Facts

• Less than 1 percent of all animals that ever lived became fossils.
• Insects trapped in amber can be preserved perfectly for millions of years.
• The oldest known fossils are tiny bacteria about 3.5 billion years old.

Did You Know?

Fossilization is extremely rare. An animal needs to be buried quickly after death, in just the right conditions. Scientists estimate that only about one bone in a billion ever becomes a fossil!