Here's why:
* Sedimentation: Rocks form in layers through the process of sedimentation. Sediments like sand, mud, and organic matter accumulate over time, layer upon layer.
* Time: Each layer represents a specific period in Earth's history. The oldest layers are deposited first, followed by progressively younger layers.
* Exceptions: This principle is generally true, but can be affected by geological processes like faulting or folding.
Therefore, in an undeformed sequence of rocks, the oldest rocks are at the bottom, and the youngest rocks are at the top.
