Final answer:
The correct answer to the question is that sediments lower in a stratigraphic sequence are older. This geological principle helps geologists determine the relative ages of rock layers and the fossils contained within them.
Step-by-step explanation:
The Geological Principle of Superposition states that sediments lower in a stratigraphic sequence are older. This principle, first articulated by Nicolas Steno in the 17th century, is a foundational concept for relative dating in geology. It posits that in layers of horizontal sedimentary rocks, the oldest layers are at the bottom with each subsequent layer being younger as one move upward. The law of superposition allows geologists to determine the relative ages of rock layers and the fossils within them, based on the assumption that lower strata have been in place for a longer period of time compared to those above.
Furthermore, artifacts or natural occurrences found within a stratum or that cut through multiple strata, in a cross-cutting relationship, are considered younger than the layers they are within or cut across. This is because these layers must exist first before they can be interrupted or altered by subsequent geological or anthropogenic events. Therefore, the correct answer to the student's question is that sediments lower in a stratigraphic sequence are older (option a).