An index fossil scientists determine which of the following?
a) the age of the rock layer in which it was found
b) the minerals that make up the rocks found in that layer
c) the time it took the rock to form the depth of the rock layer in which it was found

A) the age of the rock layer in which it was found

Explanation:

According to my research on studies conducted by geologists, I can say that based on the information provided within the question an index fossil helps scientists determine the the age of the rock layer in which it was found. This is because an Index fossils are fossils used to define and identify geologic periods.

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