Question

a geologist finds four layers of sedimentary rock. she determines that no geologic events have shifted the layers. she labels the layers a, b, c, and d from the top to the bottom. which statement about these layers is accurate? ○ a is older than b. ○ b is older than c. ○ c is younger than a. ○ b is younger than d.

Explanation:

In undisturbed sedimentary rock layers (no geologic events shifted them), the principle of superposition applies: the oldest layers are at the bottom, and younger layers are on top. The layers are labeled A (top), B, C, D (bottom). So D is the oldest, then C, then B, then A (youngest). Let's analyze each option:

• "A is older than B": A is on top of B, so A is younger than B. Incorrect.
• "B is older than C": B is on top of C, so B is younger than C. Incorrect.
• "C is younger than A": C is below A, so C is older than A. Incorrect.
• "B is younger than D": D is at the bottom (oldest), B is above D, so B is younger than D. Correct.

Answer:

D. B is younger than D