Index fossils are most useful because they .

A. occur in all rock types
B. occur over a brief time interval
C. occur over a small geographic area
D. occur over a long period of time are difficult to identify

occur over a brief time interval

Explanation:

Hi, index fossils are easily identifiable fossils distributed in a wide geographic area. Their most important characteristic is their short geological range. It means that these types of fossils occur over a brief time interval when the organism was present on earth.

The shortest the lifespan the more valuable the fossil is.

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its ok