Question

An index fossil is a relatively short-lived species in geologic history. Why does this characteristic make an index fossil useful to date rock?

Because the organisms didn't live for a long interval, they are only found in igneous rock.

Because they were short-lived, they didn't live at the same time as other organisms.

Because they lived for a short time, scientists struggle to find many of these fossils.

Because the organisms lived for only a short time, their fossils are found in a narrow range.

Answer 1

Correct answer: "Because the organisms lived for only a short time, their fossils are found in a narrow range."

Explanation: A short-lived species has a narrow time (stratigraphic) range, so finding its fossil in a rock layer indicates that layer formed during that specific, limited interval — making it a good time marker for dating and correlating rock layers.