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# Professor Robinson: A large meteorite impact crater in a

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

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20 Jul 2010, 14:37
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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 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.

Each of the following is an assumption on which Professor Robinson’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.
[Reveal] Spoiler: OA

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Last edited by broall on 22 Jun 2017, 23:37, edited 1 time in total.
Reformatted question

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

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20 Jul 2010, 15:05
noboru wrote:
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 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.
Each of the following is an assumption on which Professor Robinson’s argument depends EXCEPT:

Points mentioned
Large crater-plant and ani extinction
molten rocks crystalize-display polarity of earth.
BUT polarity found normal-expected opposite.
The only option that was not covered is whether the impact was large enough to have caused the extinction.
Didnt see EXCEPT, chose E, but E is inferred as the passsage states that the extinction was assumed to happen after impact, so its reasonable to assume that the extinction could have occured immediately

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

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21 Jul 2010, 02:39
Narrowed down to A & B easily as all rest appear clear assumptions.

(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.

Eliminated A as an assumption as this is what the author is trying to prove.

And then B is more like an assumption which should be true for rocks to reflect the magnetic field from the rocks, formed during the time of the crater formation.
Thus A
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Re: Professor Robinson: A large meteorite impact crater in a [#permalink]

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24 Jul 2010, 15:28
I chose A too (nervously though)

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

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27 Jul 2010, 23:03
Chose D .........but frankly didn't understand the options and their inference ....................

A......I just don't understand why ?

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

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09 Aug 2010, 09:34
by POE i went for A....was very doubtful though!

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

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12 Jan 2015, 20:26
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 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.
Each of the following is an assumption on which Professor Robinson’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.

Please help me understand how is the discovery of RECRYSTALLIZED rocks impacting the argument , when we are talking about "When molten rocks crystallize, they display the polarity of Earth’s magnetic field at that time". Also, please help me understand me the answer as well.

Last edited by broall on 22 Jun 2017, 23:34, edited 1 time in total.
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Re: Professor Robinson: A large meteorite impact crater in a [#permalink]

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13 Jan 2015, 11:54
Fact : Meteorite impact crater was the clue to explain the mass extinction of plant and animal.
Conclusion : The impact that formed this crater was not the culprit(for mass Extension)
Supporting Fact : Earth’s magnetic field was reversed at the time of the mass extinction. The recrystallized rocks recovered at the site display normal magnetic polarity(Not reversed Magnetic field) Hence ~ Conclusion.

The Author is trying to tell Ideally if the meteorite impact caused the extinction Those Rocks that are Crystallized(after impact) should have the same reversed Magnetic Field(as that of Earth's). Just because they do not have the author is concluding that meteorite impact did not cause Extension.

Assumption Question should always be approached using Negation Technique: In this Question those Choices that Weaken the Argument when negated should be eliminated

(B) The recovered rocks recrystallized shortly after they melted.
Negation: The recovered rocks did not recrystallized shortly after they melted: This Weakens the Argument as it provides a possibility that: "Impact resulted in Extension and resulted in reversal in Earth’s Magnetic Field , but at the same time explains why the Rocks did not have reversal in Magnetic Field(as they did not Crystallize immediately)" [Alternate Cause]

(C) No other event caused the rocks to melt after the impact formed the crater.
Negation:Other event caused the rocks to melt after the impact formed the crater : This also weakens the Argument as it creates the new possibility that after the impact occurred the Rocks are melted again Crystallized again [Data Error]

(D) The recovered rocks melted as a result of the impact that formed the crater.
Negation: The recovered rocks did not melt as a result of the impact that formed the crater. This also weakens the Argument(It is actually similar to Option B) [Alternate Cause]

(E) The mass extinction would have occurred soon after the impact that supposedly caused it.
Negation: The mass extinction did not occurred soon after the impact that supposedly caused it: This Weakens the argument Ex: The Creates the possibility that meteorite impact further caused Chain of actions that caused the Extension

Hence A is the answer.

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

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29 Sep 2015, 18:25
noboru wrote:
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 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.
Each of the following is an assumption on which Professor Robinson’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.

Though not sure.. i guess the wording in A makes it wrong..

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

no need to be more than suff size.. can create mass extinction even if the crater is of suff size..

Experts please check in..

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

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16 Jun 2017, 09:36
3
This post was
BOOKMARKED
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 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.

Each of the following is an assumption on which
Professor Robinson’ 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.

Source: LSAT
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Last edited by broall on 22 Jun 2017, 23:35, edited 1 time in total.
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Re: Professor Robinson: A large meteorite impact crater in a [#permalink]

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16 Jun 2017, 13:59
1
KUDOS
This is an arduous question as we are looking for 4 assumptions among non-assumptions, so it might take more time to answer. However, it's clear why A is the answer as the size of the impact that caused the crater is irrelevant to whether the crater can explain the extinction. The other options somehow connected the premise to the conclusion.

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

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19 Jun 2017, 13:44

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

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22 Jun 2017, 18:49
IIMC wrote:

This is a confusing passage, so let's start with the conclusion: "the crystalline structure of rocks recovered at the [impact] site indicates that the impact that formed this crater was not the culprit" responsible for the mass extinction of plant and animal species that occurred at the end of the Mesozoic era.

What is the point of this passage?

The first sentence describes an explanation that had previously been accepted: "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, evidence from the "the crystalline structure of rocks recovered at the site" goes against that explanation. So, there was a commonly held view, and then new evidence suggested that the prevailing view was not accurate.

What was that evidence?

• The "Earth’s magnetic field was reversed at the time of the mass extinction."
• "The recrystallized rocks recovered at the [impact] site display normal magnetic polarity."
• "When molten rocks crystallize, they display the polarity of Earth’s magnetic field at that time."
• Thus, we can infer that the rocks recovered at the site--if they were molten--did not crystallize at the time of the mass extinction.
• In other words, if molten rock was in fact created by the meteorite impact and if that impact occurred at the time of the extinction, then we would expect the recrystallized rocks recovered at the site to display reversed magnetic polarity. Thus, according to the author, the fact that the rocks display normal magnetic polarity is evidence that the impact that formed the crater was not the cause of the mass extinction.

Each of the following is an assumption on which Professor Robinson’s argument depends EXCEPT:

(A) The author argues that the evidence from the rocks suggests that the impact that formed the crater was NOT the cause of the mass extinction. If (A) were not true, then it would be further evidence to SUPPORT the author's argument. Thus, (A) is not a required assumption and might be our answer.

(B) What if the meteorite did cause the extinction at a time when the magnetic field was reversed, but then it took thousands of years for the molten rocks to recrystallize? By that time, the Earth's magnetic field may have returned to normal, explaining why the recrystallized rocks recovered at the impact site display normal magnetic polarity. This would disrupt the author's logic, so (B) is a required assumption.

(C) What if the molten rocks crystallized at the time of the extinction (giving them reversed magnetic polarity), but then, years later, when the magnetic field was normal, the rocks melted again and recrystallized? That would explain why the recrystallized rocks recovered at the impact site display normal magnetic polarity, disrupting the author's logic. (C) is a required assumption.

(D) If the rocks did not melt as a result of the impact that formed the crater, then their polarity would not be an indication of the Earth's polarity at the time of the impact. Thus, the crystalline structure of the rocks recovered at the site would be irrelevant, and the author's argument would fall apart. (D) is a required assumption.

(E) Perhaps the impact occurred at a time when the Earth's polarity was normal, but it took hundreds or thousands of years for the effects of that impact to finally cause the mass extinction. For example, maybe the impact set off a chain reaction that would, after hundreds of years, significantly alter the temperature of the planet, thus causing a mass extinction. By the time the extinction took place, the polarity of the Earth may have become reversed. This would explain why the polarity of the recrystallized rocks recovered at the impact site does not match the polarity of the Earth at the time of the extinction. Thus, (E) is a required assumption.

Only (A) is not a required assumption, so (A) is the best answer.
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Re: Professor Robinson: A large meteorite impact crater in a   [#permalink] 22 Jun 2017, 18:49
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# Professor Robinson: A large meteorite impact crater in a

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