Question

what characteristics does an index fossil need?
a. only widespread
b. short - lived, abundant, and widespread
c. only abundant
d. only short - lived

Explanation:

Index fossils are used to define and identify geologic periods. They need to be short - lived (so they represent a narrow time range), abundant (to be easily found), and widespread (so they can be used across different locations). Option A only mentions widespread, which is insufficient. Option C only mentions abundant, which is also not enough. Option D only mentions short - lived. Option B combines all the necessary characteristics.

Answer:

B. short - lived, abundant, and widespread