What do fossils found in deeper rock layers usually indicate?

Correct answer: They may be relatively older

The relevant geological principle is superposition: in an undisturbed sequence of sedimentary rock, lower layers were generally deposited before the layers above them. Consequently, fossils preserved in deeper layers are usually relatively older than fossils in higher layers. The word “may” is important because folding, faulting and disturbance can alter the original order. Thus A is the scientifically careful answer.