This is based on the principle of superposition, which states that in undisturbed rock sequences, the oldest rocks are at the bottom and the youngest rocks are at the top.
Here's why:
* Sedimentation: Rocks form through the accumulation of sediment over time. As new sediment layers are deposited, they bury the older layers below.
* Time: Each layer represents a specific period of time in the Earth's history. The lower layers represent earlier times, and the upper layers represent later times.
* Fossils: Fossils are preserved remains of organisms. They are trapped in the sediment layers when they form. Therefore, the fossils in lower layers are older than those in higher layers.
Exceptions:
While superposition is a reliable principle, there are some exceptions:
* Folding and Faulting: Geological processes can distort rock layers, making it difficult to determine their original order.
* Intrusive Igneous Rocks: Magma can intrude into existing rock layers, displacing them.
However, in most cases, superposition remains a fundamental principle for determining the relative ages of fossils and rocks.
