Question

For many years, biologists thought a certain frog species had gone extinct in a region because no individuals were found after a fungal outbreak. This belief was based on surveys conducted after the outbreak, which failed to detect any frogs. However, researchers recently found the species' remains buried in soil layers that appear to have been deposited after the time of the outbreak, suggesting the species might have survived longer than previously believed. This finding does not necessarily disprove the original belief, because \underline{\hspace{1cm}.}

• A. earlier surveys did not cover some of the more remote wetlands in the region
• B. other frog species in the area recovered quickly after the outbreak subsided
• C. sediment layers can contain remains of animals that died years before the layers were deposited
• D. the frog species is known to have a patchy and irregular distribution even in stable environments
• E. DNA from the fungus was also found in the same sediment layers as the frog remains

Hint:

When asked to resolve a paradox or explain why new evidence doesn't disprove an old theory, look for an answer choice that attacks the central assumption of the new evidence. Here, the assumption is that the location of remains directly corresponds to the time of death.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
This is a "Complete the Argument" question. We need to find a reason why the new evidence (remains in later soil layers) might be misleading, thereby explaining why the original belief (extinction at the time of the outbreak) could still be correct.
Step 2: Detailed Explanation
Let's break down the logic:

Original Belief: Frogs went extinct during the outbreak (Time T). Evidence: No frogs found in surveys after Time T.
New Evidence: Frog remains found in soil layers deposited *after* Time T.
New Suggestion: The frogs survived past Time T.
The Task: Find a reason why the New Evidence doesn't disprove the Original Belief. This means we need to find a way to break the link between "remains in later soil" and "lived at a later time."
How could remains of an animal that died at Time T end up in a soil layer deposited at Time T+50? This could happen if the remains were moved and redeposited by geological or biological processes.
Step 3: Final Answer
Let's analyze the options:

(A) This would suggest the original surveys were flawed, which would actually *strengthen* the idea that the frogs survived. It weakens, not explains, the counter-argument.
(B) and (E) are irrelevant to the timing of the specific species' extinction.
(D) This explains why the original surveys might have missed the frogs, again strengthening the idea they survived.
(C) This directly attacks the assumption behind the new evidence. If remains can be moved from an older location and redeposited in a newer soil layer, then finding remains in a "post-outbreak" layer does not prove the frog was alive in the "post-outbreak" period. The frog could have died during the outbreak, and its bones were later washed into the newer sediment. This allows both the original belief and the new finding to coexist without contradiction.
Option (C) provides a perfect explanation for how the new evidence could be misleading, thus resolving the apparent conflict.