Question

x and y in the diagram above are both marine fossils
which of the following best describes the diagram above?
marine fossil x most likely lived after marine fossil y died.
marine fossil y most likely lived after marine fossil x died.
both marine fossils most likely lived at about the same time.
both marine fossil x and y died during the permian extinction event.

Explanation:

To determine the relative timing of marine fossils X and Y, we analyze the geological layers. The diagram shows a fault (the diagonal line) that has displaced the layers. Fossil X is in a layer that, before faulting, was at the same level as the layer containing Y but shifted. However, the key is the original deposition: the layer with X was deposited first, then the fault occurred, and later the layer above Y (but Y's layer was originally at the same time as X's? No, wait—actually, the fault has moved the layers. But the critical point is that the layer containing X, before faulting, was horizontal, and the fault caused the right side to drop? Wait, no, the diagram shows that the brick layer with X is on the left, and the brick layer with Y is on the right, with a fault. The original layers were horizontal, so the layer with X and the layer with Y were part of the same horizontal layer before faulting. But then a fault occurred, and later, maybe? Wait, no—fossils in the same original horizontal layer (before faulting) would be from the same time. But the fault has displaced them. However, the option "Both marine fossils most likely lived at about the same time" is correct because they are in layers that were originally part of the same horizontal stratum (before the faulting event), meaning they were deposited at the same time, and the fault later displaced the layers. The other options: X living after Y or Y after X would require different layer deposition times, but the layers were originally the same. The Permian extinction is not indicated here.

Answer:

Both marine fossils most likely lived at about the same time.