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:

To determine the relative ages of rock layers, we use the principle of superposition (younger layers are on top of older ones) and index fossils (fossils that help correlate layers of the same age).

• For "Layer 8 is older than layer 1": Layer 1 is above Layer 8, so Layer 1 is younger, meaning Layer 8 is older? Wait, no—superposition: older layers are below younger. Wait, Layer 1 is on top of Layer 2, which is on top of Layer 3, etc. Wait, the fault has displaced the layers. Let's look at index fossils. Layer 2 has a shell fossil, Layer 9 also has the same shell fossil. Layer 1 has a "sock" fossil, Layer 8 also has the same "sock" fossil. Layer 3 has a cone fossil, Layer 10 has the same cone fossil. Layer 4 and Layer 7 have the same oval fossils.

Now, let's analyze each option:

1. "Layer 8 is older than layer 1": Layer 1 is above Layer 8? Wait, no—looking at the diagram, the left side (layers 1 - 5) and right side (layers 6 - 10) are separated by a fault. The left layers: 1 (top), 2, 3, 4, 5 (bottom). The right layers: 6 (top), 7, 8, 9, 10 (bottom). Now, the index fossils: Layer 1 (sock) and Layer 8 (sock) should be same age? Wait, no—superposition: on the left, 1 is top (youngest), 5 is bottom (oldest). On the right, 6 is top (youngest), 10 is bottom (oldest). But the fault has moved the layers. Wait, the key is index fossils. Layer 2 (shell) and Layer 9 (shell) have the same fossil, so they are same relative age. Let's check each option:

• "Layer 8 is older than layer 1": Layer 1 is on the left, top; Layer 8 is on the right, below Layer 7 and 6. But Layer 1's fossil (sock) is same as Layer 8's? Wait, no—Layer 1 (sock) and Layer 8 (sock) would be same age? But Layer 1 is above Layer 2, which is above Layer 3, etc. Wait, maybe I got the layers reversed. Wait, the left side: 1 is top, 5 is bottom. The right side: 6 is top, 10 is bottom. The fault is a diagonal line. So the left layers 1 - 5 are older or younger? Wait, no—sedimentary layers are deposited over time, so older layers are below younger. So on the left, 5 is oldest, 1 is youngest. On the right, 10 is oldest, 6 is youngest. Now, the index fossils: Layer 2 (shell) and Layer 9 (shell) – so Layer 2 (left, above Layer 3) and Layer 9 (right, above Layer 10) – since they have the same fossil, they are same relative age. Let's check other options:

• "Layer 3 is younger than layer 6": Layer 3 is on the left, below Layer 2 and 1; Layer 6 is on the right, top. Layer 3 is older than Layer 6 (since 3 is below, 6 is top), so this is false.

• "Layer 4 and layer 10 are the same relative age": Layer 4 (left, below Layer 3) has oval fossils; Layer 10 (right, bottom) has cone fossil. Different fossils, so not same age.

• "Layer 2 and layer 9 are the same relative age": Layer 2 (left) and Layer 9 (right) have the same shell fossil, so they are same relative age. This is correct.

Answer:

Layer 2 and layer 9 are the same relative age.