Evidence About Earth’s Past (Book)

Index fossils are commonly used to match rock layers in different places. You can see how this works in Figure. If two rock layers have the same index fossils, then they’re probably about the same age.

Using Index Fossils to Match Rock Layers. Rock layers with the same index fossils must have formed at about the same time. The presence of more than one type of index fossil provides stronger evidence that rock layers are the same age.