Question

this diagram shows fossils in an undisturbed sedimentary rock sequence.
shallower
deeper
which of the following fossils is older? select the more likely answer.
mammal tooth
wood

Explanation:

Step1: Recall the principle of superposition

In undisturbed sedimentary rock layers, the deeper layers are older than the shallower ones because sediment accumulates over time, with new layers forming on top of older ones.

Step2: Identify the layers of each fossil

• The mammal tooth fossil is in the top (shallower) brown layer.
• The wood fossil is in the middle gray layer, which is deeper than the top layer but shallower than the bottom brown layer. Wait, no, wait: Wait, the bottom layer (deeper) has the footprint - like fossil, the middle layer has the wood - like fossil, and the top has the mammal tooth. Wait, no, the diagram: the vertical axis is shallower (top) to deeper (bottom). So the layers from top (youngest) to bottom (oldest) are: top brown layer (mammal tooth), middle gray layer (wood), bottom brown layer (footprint). Wait, no, the question is between mammal tooth and wood. Wait, the wood is in the middle layer, which is deeper than the top layer (where mammal tooth is). But wait, the deeper the layer, the older the fossil. Wait, no: the bottom layer is the oldest, then middle, then top. So the wood is in the middle layer, mammal tooth in top. But wait, the other fossil (footprint) is in the bottom (deepest, oldest). But the question is between mammal tooth and wood. Wait, no, maybe I misread. Wait, the two options are mammal tooth (top layer) and wood (middle layer). Wait, no, the middle layer is deeper than the top, so the wood fossil is in a deeper (older) layer than the mammal tooth? Wait, no, the bottom layer is deeper (older) than middle, which is older than top. So middle layer (wood) is older than top layer (mammal tooth). Wait, but wait, maybe the wood is in the middle, mammal tooth in top. So wood is older. But wait, let's check again. The diagram: the left vertical arrow: shallower at top, deeper at bottom. So the layers: top (shallowest, youngest) is brown with mammal tooth; middle is gray with wood; bottom (deepest, oldest) is brown with footprint. So between mammal tooth (top layer) and wood (middle layer), the wood is in a deeper (older) layer. Wait, but maybe the question is about the two options: mammal tooth and wood. Wait, no, maybe I made a mistake. Wait, the principle of superposition: in undisturbed sedimentary rocks, the oldest layers are at the bottom, and younger layers are on top. So the fossil in the deeper layer is older. So the wood is in the middle layer, which is deeper than the top layer (mammal tooth). So wood is older than mammal tooth. Wait, but let's confirm. The top layer (mammal tooth) is younger than the middle layer (wood) because middle is deeper. So the wood fossil is in a deeper (older) layer than the mammal tooth. Therefore, wood is older. Wait, but maybe the other fossil (footprint) is older, but the options are mammal tooth and wood. So between these two, wood is in a deeper layer, so older.

Wait, no, wait: the vertical axis is shallower (top) to deeper (bottom). So the order of layers from youngest to oldest is: top layer (youngest), middle layer (older than top), bottom layer (oldest). So the fossil in the middle layer (wood) is older than the fossil in the top layer (mammal tooth). Therefore, wood is older.

Answer:

The wood fossil (the one labeled "wood") is older. But in the options, the two are: A. mammal tooth, B. wood. So the correct answer is B. wood (the option with the wood - like fossil, the second option). Wait, the options are: first option is mammal tooth (top layer), second is wood (middle layer). So the wood is in a deeper (older) layer than the mammal tooth, so wood is older.

Wait, but maybe I messed up. Let's re - state:

1. Principle of superposition: In undisturbed sedimentary rock sequences, the oldest layers are at the bottom, and younger layers are deposited on top.

1. The mammal tooth fossil is in the top (shallowest) layer.

1. The wood fossil is in the middle layer, which is deeper (and thus older) than the top layer.

Therefore, the wood fossil is older than the mammal tooth fossil.