CORRELATING ROCK LAYERS online exercise for - Free Printable

Problem Analysis and Solution

The task involves correlating rock layers from two different sites (Site #1 and Site #2) based on fossil types and understanding geological principles such as stratigraphy, unconformities, and absolute dating. Let's solve each question step by step.

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#### 1. Understanding the Rock Layers and Fossils
- Site #1:
- Layers: K, L, M, N, O
- Fossils:
- Layer K: Fossil (5 million years old)
- Layer O: Wing-shaped clam fossil
- Unconformity: Between layers N and M.

- Site #2:
- Layers: A, B, C, D, E, F
- Fossils:
- Layer B: Fossil (6 million years old)
- Layer D: Wing-shaped clam fossil

#### 2. Which layer at Site #1 is the oldest?
- In stratigraphy, the oldest layers are at the bottom, and the youngest are at the top.
- At Site #1, the layers are ordered from top to bottom as: K, L, M, N, O.
- Therefore, the oldest layer at Site #1 is O.

Answer to Question 2: O

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#### 3. Which layer at Site #2 is the oldest?
- Similarly, at Site #2, the layers are ordered from top to bottom as: A, B, C, D, E, F.
- Therefore, the oldest layer at Site #2 is F.

Answer to Question 3: F

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#### 4. Which layer is the oldest of them all?
- From Question 2, the oldest layer at Site #1 is O.
- From Question 3, the oldest layer at Site #2 is F.
- Absolute dating shows that the fossil in layer B (Site #2) is 6 million years old, which is older than the fossil in layer K (Site #1), which is 5 million years old.
- Since layer F is below layer B, it must be older than 6 million years.
- Therefore, the oldest layer of them all is F.

Answer to Question 4: F

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#### 5. An unconformity exists between two layers at Site #1. Which layer of rock at Site #2 corresponds to the missing layer due to the unconformity?
- An unconformity at Site #1 occurs between layers N and M, meaning there is a gap in the rock record where some layers are missing.
- To find the corresponding layer at Site #2, we need to match the fossils and rock types above and below the unconformity.
- Above the unconformity (layer N), the wing-shaped clam fossil is found in sandstone (layer O).
- Below the unconformity (layer M), no specific fossil is mentioned, but we can infer the rock type and age.
- At Site #2, the wing-shaped clam fossil is also found in limestone (layer D). This suggests that the missing layer (between N and M at Site #1) corresponds to the layer above D at Site #2, which is layer C.

Answer to Question 5: C

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#### 6. What is the approximate age of layer B, at Site #2?
- Absolute dating shows that the fossil in layer B is 6 million years old.
- Therefore, the approximate age of layer B is 6 million years.

Answer to Question 6: 6 million years

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#### 7. The wing-shaped clam fossil is found within sandstone in layer O, and within limestone in layer D. What is one possible explanation for why they are not found in the same type of rock?
- The presence of the wing-shaped clam fossil in both sandstone (layer O) and limestone (layer D) suggests that the clams lived in environments suitable for both rock types.
- Sandstone typically forms in fluvial (river) or coastal environments, while limestone forms in marine (ocean) environments.
- One possible explanation is that the environment changed over time, leading to different rock formations:
- Initially, the area might have been a shallow marine environment where limestone formed, and clams lived there.
- Later, the environment may have shifted to a river or coastal setting, leading to the formation of sandstone, where clams continued to live.
- Another possibility is that the clams were transported by water currents and deposited in different environments, leading to their presence in both rock types.

Answer to Question 7: The environment changed over time, leading to different rock formations (e.g., from marine to fluvial/coastal), or the clams were transported by water currents and deposited in different environments.

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Final Answers:

1. O
2. F
3. C
4. 6 million years
5. The environment changed over time, leading to different rock formations, or the clams were transported by water currents and deposited in different environments.

Boxed Final Answers:
1. \boxed{O}
2. \boxed{F}
3. \boxed{C}
4. \boxed{6 \text{ million years}}
5. \boxed{\text{The environment changed over time, leading to different rock formations, or the clams were transported by water currents and deposited in different environments.}}