2. Is the intrusion (layer D) older or younger than layer A? Why? (2 points)
Based on the principle of superposition, intrusion layer D is younger than layer A.
Intrusion layer D is a type of intrusion, which means it is a mass of igneous rock that has been injected into the surrounding rock layers. This intrusion process occurs after the deposition and formation of the surrounding rock layers, including layer A.
According to the principle of superposition, in undisturbed rock sequences, younger rock layers are deposited on top of older layers. Since intrusion layer D cuts across layer A, it can be concluded that intrusion D is younger than layer A as intrusion D must have been injected after the formation of layer A.