Logical Reasoning

PT111 · S1 · Q16 On the basis of the available

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On the basis of the available evidence, Antarctica has generally been thought to have been covered by ice for at least the past 14 million years.

Conclusion

The Antarctic ice sheet must temporarily have melted about three million years ago — i.e., Antarctica has not been continuously ice-covered for the last 14 million years.

Evidence

Three-million-year-old ocean-floor-sediment fossils were found beneath the central Antarctic ice sheet. Either severe climatic warming or volcanic activity could have melted the ice and submerged the continent (which is what would have allowed those fossils to settle into ocean-floor sediments at that location).

Evaluate

Identify the main conclusion vs. supporting claims. The "either-or" sentence about volcanic activity or climatic warming is offered as support for the melting-ice claim ("after all, ..."). The melting-ice claim is the main conclusion the author is arguing for; the previous-belief framing (14M years of ice) sets up the contrast.

Goal

Find the answer that captures the claim "the ice melted three million years ago" — i.e., the ice sheet has not been continuously present.

16.

Which one of the following is the main conclusion of the argument?

  1. Antarctica is no longer generally

    Bad Conclusion Match

    This is about what is "generally thought" — a claim about people's current beliefs. The author's conclusion is about what actually happened to the ice sheet, not about how widespread some belief is. (And in fact, the stimulus opens with "has generally been thought" — there is no evidence the author is making a sociological claim about whether the belief is now generally held.) Off target.

    12% picked this

  2. It is not the case

    Bad Conclusion Match

    This is a side claim about where these fossils can be found, not the author's main point. The author uses the fossils as evidence to argue something about the ice sheet — that it must have melted. The claim about fossil distribution is a stepping stone, not the destination.

    1% picked this

  3. Correct

    The ice sheet covering Antarctica

    Why this is right

    This is exactly the main conclusion. The author argues that the ice sheet must have temporarily melted three million years ago — which is just to say that the ice has not been continuously present for the last 14 million years. The author signals it with "therefore," and the rest of the stimulus (background about prior belief, plus "after all" supporting reasons) all serves this claim.

    Skill tested: Main Conclusion · how this choice captures the argument's function is the move to repeat next time.

    73% picked this

  4. What caused Antarctica to be

    Bad Conclusion Match

    This claim — that ice melting caused the submersion — appears in the stimulus only as part of the supporting "after all" reasoning, not as the main point. The author is concluding that the ice melted, not making a separate point about what specifically caused the continent to submerge. (The submersion is part of the chain explaining how the fossils ended up where they did.)

    5% picked this

  5. The ice sheet covering Antarctica

    Bad Conclusion Match

    This identifies why the ice would have melted (volcanic activity or climatic warming) — but that's the author's supporting evidence, not the conclusion. The conclusion is that the ice melted. The "either ... or" sentence is offered after "after all," which is a premise indicator.

    9% picked this

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