Solved Index Fossils Younger Bed contains and Index fossils ... - Free Printable

Let's solve each question based on the image provided, which shows a cross-section of rock layers (strata) with different fossils labeled A through F, and a chart showing fossil succession.

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1) Which fossil is the oldest? The youngest? Explain why. (2pt)

- Oldest fossil: Fossil A
- Youngest fossil: Fossil F

Explanation:
In sedimentary rock layers, the principle of superposition states that the oldest layers are at the bottom, and the youngest are at the top. Looking at the diagram:
- Fossil A appears only in the lowest layer (Layer 1), making it the oldest.
- Fossil F appears only in the topmost layer (Layer 10), making it the youngest.

So, A is the oldest, and F is the youngest because they appear in the oldest and youngest rock layers respectively.

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2) Which fossil would be the best index fossil? Explain why. (2pt)

- Best index fossil: Fossil C

Explanation:
An index fossil must be:
- Easily recognizable
- Abundant
- Widespread geographically
- But have a limited time range (i.e., existed for a short period)

Looking at the fossil succession chart:
- Fossil C appears in Layers 5–8, so it has a relatively short vertical range.
- It appears in multiple layers across a wide area (implied by the diagram), indicating good geographic distribution.
- It’s distinct and easily identifiable.

In contrast:
- Fossil B appears in Layers 4–6 → moderate range.
- Fossil D appears in Layers 5–7 → similar to C.
- Fossil E appears in Layers 6–9 → longer range.
- Fossil F appears only in Layer 10 → too narrow, but might not be abundant enough.
- Fossil A appears only in Layer 1 → too old and limited.

But C has a good balance — widespread and short-lived, making it ideal for correlation.

✔ So, Fossil C is the best index fossil due to its limited time range and broad occurrence.

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3) You have a collection of fossils C and E, which came from the same location. Which layer did these fossils likely come from? (2pt)

- Likely layer: Layer 6 or 7

Explanation:
- Fossil C appears in Layers 5, 6, 7, and 8
- Fossil E appears in Layers 6, 7, 8, and 9

The overlap between these two fossils is in Layers 6, 7, and 8.

Since both fossils were found together at the same location, they must come from a layer where both coexist.

Therefore, they likely came from Layer 6, 7, or 8.

But since we're asked for which layer, and there's no way to determine exact layer without more data, the most likely answer is Layer 7, as it's central to the overlapping range and contains both fossils.

However, if the question allows for a range, the correct answer is any of Layers 6, 7, or 8.

But since it says “which layer”, and assuming one specific layer, Layer 7 is the best choice.

✔ Answer: Layer 7

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4) You have a collection of fossils A, D, and F – could these have all come from the same layer? Explain. (2pt)

- No, they could not have all come from the same layer.

Explanation:
Check the stratigraphic ranges:
- Fossil A: Only in Layer 1
- Fossil D: In Layers 5–7
- Fossil F: Only in Layer 10

These three fossils appear in completely different layers and do not overlap in any single layer.

Therefore, they cannot have come from the same layer.

✔ Answer: No, because they exist in non-overlapping layers (A in Layer 1, D in Layers 5–7, F in Layer 10).

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✔ Final Answers:

1. Oldest: Fossil A (bottom layer); Youngest: Fossil F (top layer) — due to superposition principle.
2. Best index fossil: Fossil C — short time range, widespread, easily identifiable.
3. Layer: Layer 7 (or 6–8) — only layers where both C and E coexist.
4. No — A, D, and F do not occur in any common layer; their time ranges don’t overlap.

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