Question

Fossils of the coral Acrocora palmata that date from the last period when glaciers grew and consequently spread from the polar regions are found at ocean depths far greater than those at which A. palmata can now survive. Therefore, although the fossilized A. palmata appears indistinguishable from A. palmata now living, it must have differed in important respects to have been able to live in deep water.
The argument depends on the assumption that

• A. no fossils of the coral A. palmata have been found that date from periods when glaciers were not spreading from the polar regions
• B. geological disturbances since the last period during which glaciers spread have caused no major downward shift in the location of A. palmata fossils
• C. A. palmata now live in shallow waters in most of the same geographical regions as those in which deep-lying A. palmata fossils have been found
• D. A. palmata fossils have been found that date from each of the periods during which glaciers are known to have spread from the polar region
• E. A. palmata can live at greater depths where the ocean temperature is colder than they can where the ocean temperature is warmer

Hint:

To find the necessary assumption in an argument, look for a statement that rules out a major alternative explanation. Here, the conclusion is that the organism was different. The alternative explanation is that the environment changed (the sea floor sank). The correct assumption is the one that denies this alternative. You can use the Negation Test: if you negate option (B), it says geological disturbances DID cause a downward shift. This would destroy the argument's conclusion, proving that (B) is a necessary assumption.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
This is an assumption question. The argument concludes that an ancient version of a coral must have been biologically different from its modern counterpart. We need to find the unstated assumption that the argument relies on to make this conclusion.
Step 2: Detailed Explanation:
Let's break down the argument's logic:

Premise 1: Ancient A. palmata fossils are found in deep water.
Premise 2: Modern A. palmata can only survive in shallow water.
Conclusion: Therefore, the ancient A. palmata must have been biologically different (i.e., it was adapted to deep water).
This argument assumes that the location where the fossils are found today is the same depth at which the corals lived. It rules out alternative explanations for why the fossils are in deep water. The most obvious alternative explanation is that the corals lived in shallow water, died, and then the sea floor they were on sank (or the sea level rose dramatically). The argument must assume this alternative is not true. Let's evaluate the options:

(A) The existence of fossils from other periods is not relevant to the specific comparison being made.
(B) This directly addresses the alternative explanation. The argument assumes that the fossils' current deep location is their original location and that they haven't been moved downward by geological changes. If this assumption were false (if there \textit{had} been a major downward shift), the conclusion that the coral lived in deep water would be undermined. Therefore, the argument depends on this assumption being true.
(C) The geographical region is not the central issue; the depth is.
(D) The frequency of fossil finds is not relevant to the conclusion about the coral's biological properties.
(E) This offers a potential explanation for \textit{how} the coral might have lived deep, but it's not a necessary assumption for the main argument, which is simply that the coral must have been different. The argument doesn't depend on a specific reason for the difference.
Step 3: Final Answer:
The argument's conclusion rests on the unstated assumption that the fossils have not been geologically shifted to a greater depth since the time the corals were alive.