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Information and IdeasHardInference from layered evidence

Information and Ideas practice question

Cores drilled from the lake bed show a thick layer of volcanic ash at exactly the depth where fish fossils stop appearing. Above that layer, fish fossils appear again only after several centimetres of ordinary sediment. This suggests that ____

Which choice most logically completes the text?

  1. A. an eruption wiped out the lake's fish, which returned only after some time had passed.Correct
  2. B. fish never lived in the lake.
  3. C. the ash layer was produced by the fish themselves.
  4. D. the lake dried up permanently when the ash fell.

Answer: A. an eruption wiped out the lake's fish, which returned only after some time had passed.

Fossils stop at the ash and resume only after more sediment: the ash coincides with the fish disappearing, and the gap shows time passing before they came back.

Why the other answers are wrong

B. fish never lived in the lake.
Fish fossils exist both below and above the ash.
C. the ash layer was produced by the fish themselves.
The ash is volcanic, according to the text.
D. the lake dried up permanently when the ash fell.
Sediment and fossils above the ash show the lake continued.

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