Question

1. (determining the ages of rocks)

a. layer b was formed less than 10 million years ago because it lies beneath a rock layer that is 10 million years old.
b. layer c shows discontinuity indicates two types of fossils overlap.
c. layers b and d show discontinuity because both contain invertebrates where new rock layers from them cannot form anymore.
d. layer d was formed first because it lies beneath the other layers.

Explanation:

Using the principle of superposition (a key geological rule), in undisturbed rock sequences, the oldest layers are at the bottom, formed first, with younger layers on top. Option A is incorrect because a layer beneath a 10-million-year-old layer would be older, not younger. Option B is incorrect as discontinuity (unconformity) is not defined by overlapping fossils. Option C is incorrect because discontinuity requires a gap in the rock record, not just new and old rocks meeting without such a gap. Option D aligns with the superposition principle: the lowest layer is the first formed.

Answer:

D. Layer D was formed first because it lies beneath the other layers.