Index fossils are used to date rock strata that would otherwise be very difficult to date. Which of these statements describes a key characteristic of index fossils?

They existed for a short span of time.

Explanation:

Index fossils are also referred to as the indicator fossils and they are simply used to define the faunal stages.

Some of the characteristics possessed by the index fossils include:

• geographic distribution that's wide

• short vertical range

• rapid evolutionary trends.

a. themes: sub fields