If an unconformity exists between these two layers of fossils, which statement is true?
A. It could be hard to reconstruct the habitat that existed between the times when the fossils in each layer lived.
B. Some of the fossils in the lower layer might be the same age as some of the fossils in the upper layer.
C. The organisms fossilized in both the top and bottom layers lived in the same habitat.
D. The fossils in the top layer are older than those in the bottom layer.