Iowa State Geology Practice Exam 2026 - Free Geology Practice Questions and Study Guide

The principle of superposition is a fundamental concept in geology that pertains to the relative ages of sedimentary rock layers. It posits that in any sequence of undisturbed sedimentary rocks, the layers are deposited in a time sequence, with the oldest layers located at the bottom and the youngest layers at the top. Therefore, the assertion that each layer must be younger than the one below it accurately reflects this principle.

This understanding is crucial for geologists as it helps them reconstruct the geological history of an area. It allows them to decipher the order of events in Earth's past by examining the vertical arrangement of rock layers. Thus, the statement that each layer is younger than the one below it aligns perfectly with the principle of superposition, making it the correct choice.