Visualize five horizontal sedimentary strata exposed in a cliff or canyon wall identified by consecutive numbers,1 being the lowest bed and 5 being the highest.Which of the following statements concerning the strata is true?
A)Bed 5 is the oldest.
B)Beds l and 3 are older than bed 4.
C)Bed 4 is older than bed 2.
D)Bed 3 is older than beds 2 and 4.

Question

Quizplus · Accepted Answer

The principle of superposition states that in an undisturbed sequence of sedimentary rocks, the oldest rocks are at the bottom and the youngest rocks are at the top. Therefore, bed 1 is the oldest and bed 5 is the youngest. Bed 2 must be younger than bed 1, but we don't know if it is older or younger than bed 4. Bed 3 must be younger than beds 1 and 2, so it is older than bed 4 but we don't know if it is older or younger than bed 5. Finally, we know that bed 4 is younger than beds 1 and 3, but we don't know if it is older or younger than bed 2 or bed 5. Therefore, the only statement that we can determine to be true is that beds 1 and 3 are older than bed 4.

Visualize Five Horizontal Sedimentary Strata Exposed in a Cliff or Canyon