Professor Robinson: A large meteorite impact crater in a : GMAT Critical Reasoning (CR)
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# Professor Robinson: A large meteorite impact crater in a

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VP
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Professor Robinson: A large meteorite impact crater in a [#permalink]

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29 Apr 2005, 05:55
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Professor Robinson: A large meteorite impact crater in a certain region was thought to be the clue to explaining the mass extinction of plant and animal species that occurred at the end of the Mesozoic era. However, the crystalline structure of rocks recovered at the site indicates that the impact that formed this crater was not the culprit. When molten rocks crystallize, they display the polarity of Earthâ€™s magnetic field at that time. But the recrystallized rocks recovered at the site display normal magnetic polarity, even though Earthâ€™s magnetic field was reversed at the time of the mass extinction.

Each of the following is an assumption on which Professor Robinsonâ€™s argument depends EXCEPT:

(A) The crater indicates an impact of more than sufficient size to have caused the mass extinction.

(B) The recovered rocks recrystallized shortly after they melted.

(C) No other event caused the rocks to melt after the impact formed the crater.

(D) The recovered rocks melted as a result of the impact that formed the crater.

(E) The mass extinction would have occurred soon after the impact that supposedly caused it.
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30 Apr 2005, 22:09
A. The professor clearly indicates that the crater was thought to have been the culprit.
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01 May 2005, 06:45
GOSH...

I will go for (E).
VP
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01 May 2005, 22:18
Yes

OA is A,

would anyone kindly explain?

thank you
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05 May 2005, 01:12
Yes, would someone kindly explain this one? For instance, how do we assume that the rocks recrystallized â€œshortlyâ€
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05 May 2005, 10:10
A.

The professor argues that the impact is not the cause.

The arguement says When molten rocks crystallize, they display the polarity of Earth’s magnetic field at that time. But the recrystallized rocks recovered at the site display normal magnetic polarity, even though Earth’s magnetic field was reversed at the time of the mass extinction.

If the molten rocks recrystallised after some time, this would go against his arguement. He needs to assume that the melting and recrystallisation of the rocks took place as a result of and soon after the impact. B is an assumption.

Same reason is behind C, D and E.
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05 May 2005, 11:26
chunjuwu wrote:
Yes

OA is A,

would anyone kindly explain?

thank you

I guess it's A. Because assumptions are elements in an argument that are assumed. A is clearly stated, not assumed.
05 May 2005, 11:26
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