November 16, 2004
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What are fossils?


When an animal or plant dies it is usually completely destroyed when either another animal eats it or when it decays. Sometimes the animal is buried before it is destroyed. Sometimes, the remains of the animal are preserved as fossils.

Here is a simple definition of fossils:

Fossils are the naturally preserved remains or traces of ancient life that lived in the geologic past.

Most fossils are invertebrates, that is, animals without backbones. Worms, insects, and clams are all invertebrates. 95% of all living animals are invertebrates. There were even more in the past.


  • Fossils represent the remains or traces of once-living organisms.
  • Most fossils are the remains of extinct organisms; that is, they belong to plants or animals that are no longer living anywhere on Earth.
  • The kinds of fossils found in rocks of different ages differ because life on Earth has changed through time.
There are 2 kinds of fossils

Body Fossils - include the remains of organisms that were once living. Usually only the hard parts of animals like shells and teeth and bones become fossilized. However, feathers, fur, and skin have also been found.

Trace Fossils- are the signs that organisms were once present. Trace fossils can be tracks, footprints, trails, burrows, eggs, nests, leaf impressions, and feces. Take a peek at these Images of trace fossils

There are also fossil plants. Click here to see images of plant fossils.

Fossil Plant Leaf

One thing all fossils have in common is that they are OLD, at least 10,000 years old.


Follow the diagrams to find out how fossils are formed.

Where are fossils found?

Fossils may be found almost anywhere sedimentary rocks are exposed.

Sedimentary rocks are rocks that formed when layers of sediment such as clay, mud, silt, or sand hardened over millions of years. These types of sediments settle down in lakes, swamps and oceans. This is one of the reasons why most fossils are the remains of animals who lived in or near the water.

Read about the Burgess Shale, a special location because of the soft-bodied preservation of a wide diversity of fossil invertebrate animals.


What do fossils tell us?
Rock layers can tell us Earth's history because they preserve past events. Fossils help scientists determine the age of the layered rocks. Fossils also tell us what happened in Earth's history and when it happened. Fossils can be used to recognize rocks of the same or different ages. They are clues to former life.

Learn about how earth's time is organized at Geologic Time Scale

Take a journey through the history of earth at the Geology Wing.

Who Studies Fossils?
     A paleontologist is a scientist who studies fossils. Do you want to be a paleontologist?
How do you find, identify and prepare fossils?
How fossils are collected..... How they are identified and classified ......How they are prepared.
Invertebrate fossils
You're probably familiar with dinosaur fossils, but did you know that they form only a small fraction of the millions of species that have lived on Earth?

Most of the fossil record is dominated by fossils of animals who had shells.
What is an ammonite?
Giant Ammonite

Check out these Invertebrate Fossils

Probably the most familiar fossil is the ammonite. These predators belong to the group called cephalopods, which include squid, octopus and nautilus.

Ammonites lived in the seas between 415 - 65 million years ago, then became extinct along with the dinosaurs.

Photos and more

What are the earliest fossils?
Earth is about 4.6 billion years old.

The oldest known fossils are from rocks from about 3.5 billion years ago.

At Shark Bay, Australia you can see stromatolites – literally layered rocks, which are examples of what the earliest life on earth looked like.
Stromatolites in Shark Bay
Fossils in and near Idaho

The state fossil of Idaho is the Hagerman Horse. Visit the Hagerman Fossil Beds National Monument and learn all about it!

There are even more fossils in Idaho!!

Another famous fossil in Idaho was found at Tolo Lake. Read about the Mammoths at Tolo Lake.


What are Trilobites?
Trilobite Fossil
Trilobites inhabited the Earth during the Paleozoic era. They were arthropods (like insects, spiders, and shellfish) who lived in the ocean.
Online Book
The US Geologic Survey provides an online book called, Fossils, Rocks and Time which can probably answer any more questions you might have.
So you want to be a Paleontologist??

Paleontology is fun, exciting, fascinating hard work. Find out how you can become one...

Meet a few vertebrate paleontologists

Link to
Rocks and Minerals
at Dialogue 4 Kids
Can you identify these
mystery fossils?
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