Question

the image shows sedimentary rock layers with index fossils and a fault. which statement accurately describes the rock layers? layer 8 is older than layer 1. layer 3 is younger than layer 6. layer 4 and layer 10 are the same relative age. layer 2 and layer 9 are the same relative age.

Explanation:

• Law of Superposition: In undisturbed sedimentary rock layers, the lower layers are older. But here there is a fault. However, index fossils can help determine relative age. Index fossils are fossils of organisms that lived over a relatively short period but were widespread. If two layers have the same index fossil, they are of the same relative age.
• Layer 2 and layer 9: Both have the same type of index fossil (the clam - like fossil). So, they are of the same relative age.
• Layer 8 and layer 1: Layer 1 is above layer 8 (assuming normal deposition before faulting in the non - faulted part). So layer 8 is older than layer 1 is incorrect.
• Layer 3 and layer 6: Layer 3 is below layer 6 in the non - faulted part (before considering the fault). So layer 3 is older than layer 6, not younger.
• Layer 4 and layer 10: They have different index fossils (layer 4 has the oval - shaped fossil, layer 10 has the conch - like fossil). So they are not of the same relative age.

Answer:

Layer 2 and layer 9 are the same relative age.