LSAT 35 - Section 1 - Question 16

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

This is a Main Conclusion question.

This problem is a great example of how important it is to recognize when an author’s conclusion is a response to other people’s position. The correct answer can sometimes be framed in terms of that response, rather than in terms that focus only on the author’s wording.

Here, we get a cookie cutter structure – the stimulus starts off with other people’s position.

Antarctica has generally been thought to have been covered by ice for at least the past 14 million years.

The phrase “has generally been thought” is what tells us that the author is describing what other people have generally thought.

Then, we learn about a phenomenon:

Recently, however, three-million-year-old fossils of a kind previously found only in ocean-floor sediments were discovered under the ice sheet covering central Antarctica.

What’s interesting about these fossils is that they are of a kind that has previously been found “only in ocean-floor sediments.” (If you thought the word “however” meant this statement was the conclusion, remember that “however” simply signals a shift in direction in the stimulus. While it often introduces a conclusion, it doesn’t always do so. The shift in direction here is the phenomenon that seems like it goes against the general belief described in the first sentence.)

Make sure to connect what we were just told with the general belief in the first sentence. Generally, people think that Antarctica has been covered by ice for the past 14 million years. But fossils from only 3 million years ago are somehow below the Antarctic ice sheet. And this kind of fossil has been found only in the ocean floor. How did they get there if ice covered Antarctica for 14 million years? Was there an ocean covering Antarctica at some point?

The next line of the stimulus attempts to reconcile this discrepancy by hypothesizing that:

About three million years ago, therefore, the Antarctic ice sheet must temporarily have melted.

This seems to be a conclusion for several reasons. First, it seems to be the author’s hypothesis for how the fossils got to be under the ice sheet – the ice sheet must have been melted at that time. Second, it uses the conclusion indicator, “therefore.” That means we know it’s a conclusion, but we need to determine whether it’s the main conclusion or just a subsidiary conclusion / major premise.

The next sentence confirms that the line we just read is the main conclusion:

After all, either severe climatic warming or volcanic activity in Antarctica’s mountains could have melted the ice sheet, thus raising sea levels and submerging the continent.

The first phrase, “after all,” is a support indicator that tells us the rest of the sentence is support for the previous statement (which was the author’s hypothesis about the Antarctic ice sheet having melted temporarily). The last sentence has the word “thus,” which might make you think the last sentence has a premise-conclusion structure of its own. Arguably that’s true, in which case, the last part following “thus” would be a subsidiary conclusion, since it’s offering a causal mechanism helping to explain why the author’s hypothesis about the ice sheet having melted makes sense.

But the word “thus” in the last sentence might just be introducing the second part of a causal claim, rather than a conclusion. (Language is sometimes ambiguous! Embrace it.) Consider these two statements:

“You can adjust the height of the chair, thus giving you some control over your viewing angle.”

“You can adjust the height of the chair, which gives you some control over your viewing angle.”

Are these arguments? Is the author trying to persuade you that you’ll have control over your viewing angle? Or is the author simply stating a single causal claim?: Adjusting the height of the chair will give you control over your viewing angle. (I think they’re not arguments.)

This discussion is not critical for solving this problem, since no matter what you think of the structure of the last sentence, the fact that it is introduced by “after all” will confirm that it’s all support for the statement immediately before “after all.”

Let’s look for something along the lines of “The Antarctic ice sheet temporarily melted about three million years ago.”

Answer Choice (A) Antarctica is no longer generally thought to have been covered by ice for the past 14 million years.

This can be a tempting trap, if you don’t distinguish between (1) the truth of a claim, and (2) people believing the claim is true. We know that the author’s conclusion is that the ice sheet must have melted 3 million years ago. So the author does not believe that ice covered Antarctica for 14 million years. But the author is silent on whether the belief that ice covered Antarctica for 14 million years remains the consensus belief. Most people may still believe that. And if they do, the author would point to them and say that they are wrong.

Answer Choice (B) It is not the case that ancient fossils of the kind recently found in Antarctica are found only in ocean-floor sediments.

The author’s conclusion was about ice melting…not whether the fossils are found somewhere besides ocean-floor sediments. That’s enough to eliminate this answer, and in a timed situation, you wouldn’t want to think any more deeply about it. (B) is trying to bait us into wasting time on thinking whether it’s supported by the stimulus. It seems to be true, if we assume that the recently discovered fossils found under the ice sheet are not in ocean-floor sediments. I don’t know if that’s a reasonable assumption or not. Regardless, it’s not the point of the author’s argument, which is about Antarctica and melted ice sheets.

Correct Answer Choice (C) The ice sheet covering Antarctica has not been continuously present throughout the past 14 million years.

This initially doesn’t seem appealing, since it speaks of the ice sheet not being “continuously” present, and it uses the figure 14 million years, when we were expecting an answer referring to 3 million years. However, when we consider the author’s conclusion and how it relates to the general belief in the first sentence, this answer makes sense as a paraphrase of the author’s point.

The general belief was that Antarctica was covered by ice for the past 14 million years. The author’s discussion of the fossils and how they indicate that the ice sheet must have melted 3 million years ago is designed to counter that general belief. “No, Antarctica wasn’t covered by ice for 14 million years – there was melting at some point.”

If you took away the first sentence – in other words, ignored the fact that the author’s argument was a response to the general belief – then (C)'s reference to 14 million years ago and the “continuous” presence of ice would not make much sense. But we do have to take into account the context; what the author is responding to matters on the LSAT. (C) may not be the ideal answer, but it is the one that best captures what we were looking for.

Answer Choice (D) What caused Antarctica to be submerged under the sea was the melting of the ice sheet that had previously covered the continent.

This may be tempting, since it’s supported by the stimulus. This is something the author believes. However, you should ask whether the author’s point was to tell us how Antarctica came to be under the sea, or whether it was to tell us that Antarctica was under the sea at some point. Notice that the statement about the how (the cause of the ice sheet melting) was the last sentence, which starts with the phrase “After all.” This phrase tells us that the last line is offered to support the previous statement. That’s why (D) is not correct.

Answer Choice (E) The ice sheet covering Antarctica was melted either as a result of volcanic activity in Antarctica’s mountains or as a result of severe climatic warming.

This is also a very tempting answer, since it seems part of the author’s reasoning. I’ll note two issues. The first is the same issue raised above with the correct answer (C) – the fact that the author’s argument is a response to the general belief in the first sentence matters. (E) doesn’t capture the timeframe of the melting, which is an important part of the author’s response. The author isn’t just trying to say that the ice sheet melted; it’s that the ice sheet melted within the time period that most people think it didn’t melt.

The second issue is that (E) arguably is not strongly supported by the stimulus. The author did mention severe climatic warming or volcanic activity as two things that could have caused the ice sheet to melt. But that doesn’t mean the author thinks those were in fact the only two causes. The author never said that they were providing the exclusive methods for how the ice sheet could have melted.