On the basis of the available evidence, Antarctica has generally been

Question

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

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

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

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

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

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

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

(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.

ArunSharma12 · Answer

(A) Antarctica is no longer generally thought to have been covered by ice for the past 14 million years.
 This is not true. Evidence presented in the passage do not question the length of time ice covered Antarctica

(B) It is not the case that ancient fossils of the kind recently found in Antarctica are found only in ocean-floor sediments.
 This is a fact presented in the passage

(C) The ice sheet covering Antarctica has not been continuously present throughout the past 14 million years.
 This is central idea presented by the entire passage. There were times in last 14 million years when ice was not covered over Antarctica

(D) What caused Antarctica to be submerged under the sea was the melting of the ice sheet that had previously covered the continent.
 This reasoning is presented to support the claim that Antarctica sheet must have melted

(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 a claim presented to support the main conclusion that ice was not present 3 million years ago but it is thought be covered under ice for the last 14 million years 
Ans: C

exc4libur · Answer

argument
=ant covered in ice for ≥14mln yrs
=fossils found under ice 3mln yrs ago
=thus, ice sheet must have melted temporarily
=since, either climate warm or volcanoes could've caused this

con
ans (C) "therefore, the ice sheet must have melted" is the same as "ice wasn't present continuously"

PearlNova · Answer

Can someone please explain in detail why D can't be the answer.

guddo · Answer

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. 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. About three million years ago, therefore, the Antarctic ice sheet must temporarily have melted. 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.
 
 Which one of the following is the main conclusion of the argument?

The argument uses the fossil discovery to conclude that  Antarctica’s ice sheet must have temporarily disappeared about three million years ago . The possible causes mentioned afterward  support that conclusion .

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

Incorrect. The argument challenges the idea of continuous ice coverage, but it does not say the general scientific view has already changed.

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

Incorrect. This follows from the fossil discovery, but it is not the main point of the argument.

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

Correct.   If the ice sheet temporarily melted about three million years ago, then it cannot have been continuously present for the entire 14-million-year period.

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

Incorrect. This is part of the proposed explanation for how the fossils could have reached Antarctica, not the main conclusion.

(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.

Incorrect. These are presented as possible causes of the melting, not as something the argument establishes.

Answer: (C)

egmat · Answer

Hi PearlNova,

Good question, because  (D)  does pull real words from the passage, so it  feels  like it belongs. The trick is spotting  where  those words sit in the argument.

Look at the last sentence:  "After all, either severe climatic warming or volcanic activity... could have melted the ice sheet,  thus raising sea levels and submerging the continent ."  The phrase  "After all"  is a support flag - everything after it is given as backing, not as the point being argued. Choice  (D)  is just a restatement of that final clause about melting causing submergence. So it lives  inside the supporting premise , not at the top of the argument.

How to find the real conclusion

The main conclusion is the one claim everything else is aimed at, and that isn't used to prop up anything further. Here that claim is marked by  "therefore" :  "About three million years ago, therefore, the Antarctic ice sheet must temporarily have melted."  That is exactly what  (C)  says - the ice sheet was  not  continuously present for the past  14 million  years.

Notice the direction, too. The argument's point is  that the ice melted .  (D)  instead talks about what the melting  caused  (submergence) - that's a downstream detail the author throws in while explaining how melting was even possible. A supporting detail, not the takeaway.

A quick way to test any choice as "the conclusion"

Ask  "Does the rest of the argument exist to prove this?"

-  (C) : the fossils + the  "therefore"  line all push toward it. Conclusion.
-  (D) : it sits after  "After all,"  doing the supporting. Premise-side detail.

So  (D)  is a true statement from the passage, but it's evidence and elaboration - the argument isn't built to establish it. That's why  (C)  is the main conclusion.

Answer: C

On the basis of the available evidence, Antarctica has generally been

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On the basis of the available evidence, Antarctica has generally been

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