6. Relative time is recorded in rocks.

Actually, the evidence is in the rocks!

Each of these rock layers represents a period of time in Earth's history, so the entire sequence of layers is another timeline.

This drawing makes the layers easier to see.

Can you figure out the relative order in which the layers were formed? Click on the oldest layer.

That's right! Now click on the youngest layer.

All over the world, rock layers are deposited on top of layers that were already there.

As more and more layers are deposited, the older rock layers end up at the bottom of the sequence and the newer ones toward the top.

In geology, this is referred to as the Law of Superposition.

Superposition is composed of two smaller words that can help you remember its meaning.

"Super" refers to over and "position" refers to place. So, superposition refers to new rock layers forming OVER the PLACE of old ones.

The arrow shows the relative order of the rock layers from earliest to most recent.

Now let’s look at the fossils buried within those layers.

Ooops! Think about which layer might have been formed first.   Try again.

Ooops! Think about which layer might have been formed last.   Try again.