Answer:
The principles of stratigraphy help us understand the relative age of rock layers. Layers of rock are deposited horizontally at the bottom of a lake (principle of original horizontal). Younger layers are deposited on top of older layers (principle of superposition). Layers that cut across other layers are younger than the layers they cut through (principle of cross-cutting relationships). The principle of superposition builds on the principle of original horizontal. The principle of superposition states that in an unreformed sequence of sedimentary rocks, each layer of rock is older than the one above it and younger than the one below it. Accordingly, the oldest rocks in a sequence are at the bottom and the youngest rocks are at the top.