explain how a crosscutting feature is always younger than the rock layers it cuts across?
Wouldn't it require the underlaying rock to be formed well before it was crosscut?
A crosscutting feature is always younger than the rock layers it cuts across due to the principle of cross-cutting relationships in geology. This principle states that any feature that cuts across another rock layer must be younger than the rock it cuts through.
To understand why this is the case, let's consider the formation of rock layers. Rock layers are formed over long periods of time through various geological processes like sedimentation, volcanic activity, or tectonic movements. Each new layer is deposited on top of older layers, creating a chronological sequence of rock formations.
Now, imagine a crosscutting feature like a fault or a vein that cuts across these layers. For this feature to cross through the already-existing rock layers, it must have formed after those layers were already in place. If the crosscutting feature had existed before the rock layers formed, it would have been buried and influenced the deposition of subsequent layers. But since it cuts across the existing layers, it must have formed at a later time.
In summary, the fact that a crosscutting feature intersects or cuts across rock layers indicates that it is younger than the rock layers it traverses. This principle is crucial in determining the relative ages of different geological features and establishing the sequence of events in Earth's history.