Here's why:
* Law of Superposition: This law states that in undisturbed rock sequences, the oldest layers are at the bottom and the youngest layers are at the top.
* Igneous Intrusion: This is the process where molten rock (magma) forces its way into existing rock layers.
* Observation: The observation of an igneous intrusion through a layer of sedimentary rock indicates that the sedimentary rock was already present before the intrusion occurred. Since the igneous rock "cut" through the sedimentary layers, it must be younger.
In summary: The presence of an igneous intrusion through a layer of sedimentary rock demonstrates that the igneous rock is younger than the sedimentary rock, thus supporting the Law of Superposition.
