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 sedimentary rock layers (when not shifted by geologic events), the principle of superposition states that the lower layers are older. So, from top (youngest) to bottom (oldest): A (top) < B < C < D (bottom).

• For "A is older than B": A is above B, so A is younger than B.
• For "B is older than C": B is above C, so B is younger than C.
• For "C is younger than A": C is below A, so C is older than A.
• For "B is younger than D": B is above D, so B is younger than D (correct as per superposition).

Answer:

B is younger than D.