The three fossils shown here are very useful in helping us to date the age of rocks.

Click on each of them to learn more.

Each of these fossils are found all over the world BUT they come from organisms that existed for only a specific period of time.

CLICK on each of the images to see the exact period of time these fossils were alive.

Since they were alive only during a specific period of time, that means that their fossils are found in very specific layers of rock.

A fossil found in specific layers of rock all over the world is called an index fossil.

Every time we find index fossils, we can figure out the age of the rocks they are preserved in.

Let's take a close look at one of these index fossils.