Question

What best describes index fossils?

Answer 1

The fossil remains of an organism that lived in a particular geologic age, used to identify or date the rock or rock layer in which it is found. Ammonites and graptolites are good index fossils.

Answer 2

Is an animal or plant fossil that is preserved and represent an specific geological era.

Step-by-step explanation:

The index fossils are very useful to identify some geological eras, for example, at the sea, the fossils of protista, like the ammonoids. In the soil, the presence of fossil animals like mammals, are particularly sign of the Cenozoic era.