Finding several species of fossils, rather than just one, in the same rock layer is more useful to geologists because:
A) It indicates the sediments must have been deposited at the same time when all the species were present.
B) If some of the fossils are broken, others could be used as index species.
C) If the conditions were not right for fossilization for one species, maybe the conditions were better for other fossil species.

Question

Quizplus · Accepted Answer

Finding several species of fossils in the same rock layer suggests that the sediments were deposited at the same time when all the species were present, providing a more accurate timeline for geologists.

Finding Several Species of Fossils, Rather Than Just One, in the Same