Rock layers can often help scientists compare and date fossils across a geological timeline. These layers can be affected by different Earth processes. The diagram shows a section of rock layers affected by both erosion and tectonic date movement.

Question

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Part A
Which timeline of events best explains the formation of the rock layers in the diagram?

A
Layers R—T formed →\rightarrow→ Layer T eroded →\rightarrow→ tectonic pressure pushed layers at an angle →\rightarrow→ Layers U—Z formed
B
Layer Z formed →\rightarrow→ tectonic pressure pushed layer at an angle →\rightarrow→ Layers Y—U formed Layers W—U eroded →\rightarrow→ Layers T—R formed
C
tectonic pressure pushed layers at an angle →\rightarrow→ Layers Z—U formed →\rightarrow→ Layer T formed →\rightarrow→ Layer T eroded →\rightarrow→ Layers S—R formed
D
Layers Z—U formed →\rightarrow→ Layers Z—U eroded →\rightarrow→ tectonic pressure pushed layers at an angle→\rightarrow→ Layers T—R formed
(b)

Part B
Which statement explaining the age of the rock layers best supports the answer to Part A?
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A
Rock layers that contain fossils are always the oldest rock layers and can be used to determine the ages of rock layers above them.
B
Geologic events like earthquakes can erase rock layers from the geologic timescale and make it difficult to know the ages of different rock layers.
C
Older rock layers will always be directly below younger rock layers unless they have been disturbed by geologic activity.
D
Rock layers that are the thickest are the oldest because they represent a longer span of time in which the rock layer was formed

Answer 1

Part A:

To determine which timeline of events best explains the formation of the rock layers in the diagram, we need to consider the effects of erosion and tectonic movement on the layers.

Option C makes the most sense:

• Tectonic pressure pushed layers at an angle, which suggests that a geological event occurred before the layers formed.
• Layers Z—U formed, which indicates a sequence of deposition.
• Layer T formed afterward, followed by erosion of Layer T, indicating that erosion affected the newly formed layers.
• Finally, Layers S—R then formed, which fits as a sequence after the erosion.

Therefore, C is the best choice for Part A.

Part B:

The statement that best supports the explanation in Part A relates to how the relative ages of rock layers are influenced by geological processes.

Option C is the most appropriate:

• It states, "Older rock layers will always be directly below younger rock layers unless they have been disturbed by geologic activity." This aligns with how the layers were formed and affected by tectonic pressure and erosion, indicating that the sequence of deposition was altered by these processes.

Thus, C is the best choice for Part B.

In summary:

• Part A: C
• Part B: C