Fossils of species X are found in deeper strata whereas fossils of species Y are found only in superficial strata. What can be inferred form the above information?

Fossils can be dated relative to one another by noting their positions in layers of rocks, known as strata. The fossils found in lower strata were generally deposited earlier. As fossils of X are found in the deeper strata (compared to those of Y), it can be inferred that X originated earlier than Y.