What Are Fossils? — For Kids

What Are Fossils? — Elementary

The short answer

Fossils are what is left of old life.

They were kept in rock.

They are from before the end of the last ice age.

What can a fossil be?

A fossil can be the plant or animal itself.

It can be bones or shells.

Bones and shells can change a bit.

A fossil can be a print left by a plant or animal.

One kind of print is the mold or cast of a shell.

How does a fossil form?

Fossilization is how a fossil is made.

It turns plant or animal remains into rock.

Sometimes new, harder minerals take the place of the old material.

That is called mineralization.

Hard parts help.

An animal with hard parts is more likely to become a fossil.

Soft animals are rarely fossilized.

That includes insects and worms.

Only a very tiny part of all species that ever lived became fossils.

What are trace fossils?

Trace fossils are signs of life in sedimentary rocks.

They record things that happened when a plant or animal was alive.

Footprints are trace fossils.

Burrows are trace fossils.

Coprolites are trace fossils, too. They are fossilized feces.

Where a living thing lived matters

Where a plant or animal lived is one of the biggest parts of whether it becomes a fossil.

Things that die on dry, open plains often leave little behind.

They may be eaten by scavengers.

Or they may decay fully.

Plants and animals that die in or near water can be covered fast by sediments.

That gives them a better chance to become a fossil.

Most plants and animals decompose before they can be fossilized.

Where are fossils found?

Fossils have been found on every continent on Earth.

They have been found in every geologic age.

They are found almost only in sedimentary rocks.

Igneous rocks are too hot when they form.

Plants and animals cannot live in lava or magma.

Metamorphic rocks go through heat and pressure.

That usually destroys fossil signs.

There is one special case.

Ash can fall from a volcanic eruption.

It can cover plants and animals.

If the ash has cooled enough first, they can become fossils.

Can you find a fossil near you?

Look at sedimentary rocks, if you have some nearby.

Look in building stones.

Look in polished counter tops.

Look even in sidewalks for fossil analogs.

What Are Fossils? — Middle

The short answer

Fossils are the remains of prehistoric life, especially those preserved in rock before the end of the last ice age.

What a fossil can be

A fossil might be the animal or plant itself, or the bones or shells of animals, sometimes altered, or the imprint of a plant or animal — for example the mold or cast of a shell.

How fossilization works

Fossilization, the fossil-making process, turns these plant or animal remains into rock, sometimes by replacing the material with new, harder minerals, in a process called mineralization.

Generally, if an animal has hard parts it is more likely to become a fossil, so things like insects, worms, and other soft-bodied creatures are rarely fossilized.

Overall, only a very tiny percentage of species that ever existed on Earth have been fossilized.

Trace fossils

Trace fossils are evidence of life recorded in sedimentary rocks; a record of things that happened when an animal or plant was alive.

Some examples of trace fossils include footprints, burrows, and even coprolites (fossilized feces).

Why where it lived matters

Where an animal or plant lived is one of the biggest factors in whether or not it will become a fossil.

Things that die on dry, open plains are often rapidly consumed by scavengers, or decay completely, leaving little behind to become a fossil.

The plants and animals that die in or near water can be quickly covered by sediments, increasing their chance of becoming a fossil.

This is more common in oceans than swamps, and in swamps than rivers, so the fossil record is an incomplete picture of the history of life on Earth, heavily weighted toward marine life.

In fact, most animals and plants decompose before they can be fossilized.

Where fossils are found, and why

Fossils have been found on every continent of Earth and in every geologic age and are found almost exclusively in sedimentary rocks.

Why? Igneous rocks are too hot when they form — plants and animals can't live in lava or magma — and metamorphic rocks undergo heat and pressure which generally destroy all fossil evidence.

There is one exception: sometimes ash falls from a volcanic eruption and can fossilize plants and animals that it covers, but only if it has cooled enough not to incinerate them first.

Looking for a fossil near you

Can you find a fossil near you? Look at sedimentary rocks, if you have some nearby, or in building stones, polished counter tops, or even sidewalks for fossil analogs.