Which of these is a characteristic of index fossils? found in the topmost rock layer found in many layers of the same rock have already established relative age are limited to a particular geographic location

The index fossils have already established relative age. It is for that reason they can be used to estimate the age.

An index fossil is a fossil that spans a particular geologic time and/or given environment.

These types of fossils (index fossils) can be any type of preserved remains of an organism that lived on the Earth (e.g., an animal or plant).

For example, Ammonites are used as index fossils because they live only during the Mesozoic period (approx 245-65 mya).

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