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?

In undisturbed sedimentary rock layers, the lowest layer is the oldest and each layer above it is younger. From bottom to top, the layers are D, C, B, and A, so B is younger than D. The accurate statement is “B is younger than D.”

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