What principle states that younger rock layers are found above older rock layers?

The principle that younger rock layers are found above older rock layers is known as superposition. This geological principle is foundational in the study of rock formations and strata. It is based on the idea that in an undisturbed sequence of sedimentary rocks, each layer is deposited over time, with the oldest layers at the bottom and the youngest layers at the top.

When new sediment is deposited, it naturally accumulates on top of the existing layers due to gravity. This concept allows geologists to understand the relative ages of rock layers and the history of geological events. It is instrumental in fields like paleontology and archaeology, where determining the sequence of events is crucial for understanding the Earth's history and the timeline of life.

In contrast, the other concepts involve different aspects of geology or dating methods. Uniformitarianism refers to the principle that geological processes occurring today have acted in the same way throughout Earth's history. Relative dating involves comparing the age of one rock formation to another but doesn't specifically dictate the ordering of layers, whereas absolute dating provides specific ages for rock layers through methods like radiometric dating.