Question

what is an important characteristic of an index fossil?
a. it must have lived in a very specific geographic region.
b. it must have been very large.
c. it must have lived for a short geologic period of time.
d. it must not be extinct.

Explanation:

Index fossils are used to date rock layers. A key characteristic is a short geologic lifespan (so they define a narrow time period), wide geographic distribution, and being abundant. Option A is wrong (they need wide, not specific, regions). Option B (size isn't a key trait). Option D is wrong (index fossils are extinct). So C is correct.

Answer:

C. It must have lived for a short geologic period of time.