PrepTest 111, Section 1, Question 16
On the basis of the available evidence, Antarctica(80 more words not shown)
Which one of the following(7 more words not shown)
- AAntarctica is no(15 more words not shown)
- BIt is not(18 more words not shown)
- CThe ice sheet(13 more words not shown)
- DWhat caused Antarctica(19 more words not shown)
- EThe ice sheet(22 more words not shown)
Reading the argument
The fossils need an explanation. But do they tell us exactly when the ice melted?
The author finds it strange that fossils previously found only in ocean-floor sediments are now beneath central Antarctica's ice. Melting followed by flooding could account for their presence. Still, I have questions. Could the fossils have reached this location another way? And even if the continent was submerged, does the fossils' age establish when the melting began?
Suppose the ice melted four million years ago, the area stayed submerged and these fossils were deposited three million years ago. That would fit the fossils' age without putting the melting itself at exactly the time the author identifies. This is a possibility to consider, not a claim about Antarctica's actual history.
What we’re looking for
The main-conclusion task doesn't ask us to resolve those doubts. It asks what the author is trying to establish. The fossils are offered as evidence that the ice temporarily melted about three million years ago, and the warming or volcanic activity supplies a possible way it could have happened. I'd expect an answer saying that Antarctica's ice temporarily melted about three million years ago.
Working the answers
- A
The author argues against the established view, but we don't know whether people generally have changed their minds. Publishing or presenting an argument doesn't automatically make its conclusion the new consensus. A adds a claim about what people now believe.
- B
The location of the fossils is part of the evidence, but the conclusion concerns the ice. Also, finding fossils under today's ice doesn't establish that they are outside ocean-floor sediments: the author's proposed explanation is that the area was once submerged. B doesn't capture the point that the ice cover was interrupted.
- CCorrect
If the ice sheet temporarily melted about three million years ago, it wasn't continuously present throughout the past fourteen million years. Three million years ago falls within that longer period.
This is broader than the prediction about the particular date, but it captures the main point. An answer can describe the conclusion without repeating every detail. The author's proposed interruption of the ice cover is exactly what challenges the previously accepted account of continuous coverage.
- D
This describes the proposed mechanism connecting melting to submergence. It isn't the main claim for which the fossils are offered as evidence. The author uses a possible account of how the continent could have become submerged to support the conclusion that the ice melted. D focuses on that explanatory step instead of the central claim about interrupted ice cover.
- E
The last sentence offers warming and volcanic activity as possible causes of melting. It doesn't establish that one of them definitely caused it. More importantly, the main point is that melting occurred, not a decision about which cause produced it. E turns proposed mechanisms into the conclusion.
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