Which geologic principle states that younger rocks or fossils are deposited on top of older rocks?

• A. Law of Cross-Cutting Relationships
• B. Principle of Uniformitarianism
• C. Law of Superposition
• D. Original Horizontality

Answer: (C)

In undisturbed layers of sedimentary rock, the oldest material settles at the bottom and newer material is deposited on top. This idea is the law of superposition. It lets us read a relative timeline just by the vertical order of the layers: the topmost layers are younger than the ones below.

The other ideas describe different situations. A feature that cuts through rocks (like a fault or a magma intrusion) is younger than the rocks it cuts, which isn’t about the original order of the layers themselves. Uniformitarianism is the belief that present processes have operated the same way throughout Earth’s history. Original horizontality says sediments are deposited as flat, horizontal layers, not tilted or folded. So for a sequence where younger rocks sit atop older rocks, the law of superposition best explains why.