Here's a breakdown:
* Stratigraphy is the study of layered rocks (strata) and their relationships to time.
* The principle of superposition states that in an undisturbed sequence of sedimentary rocks, the oldest rocks will be at the bottom, and the youngest rocks will be at the top.
* This is because sedimentary rocks form from the accumulation of sediment, which settles out of a fluid (like water or air). The oldest sediment is deposited first and gets buried by later sediment.
However, it's important to note:
* Disruptions: Geological processes like faulting, folding, and erosion can disrupt the original layering of sedimentary rocks. This can make it difficult to determine the relative ages of different layers.
* Not all rocks follow this rule: Igneous rocks, for example, form from the cooling and solidification of magma or lava, and their layering may not reflect their age.
So, while stratigraphy describes the layering of rocks, the principle of superposition is the key rule for understanding the relative ages of sedimentary rocks in an undisturbed sequence.
