Iridium, a hard, whitish metal similar to platinum, is : GMAT Critical Reasoning (CR)
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# Iridium, a hard, whitish metal similar to platinum, is

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Iridium, a hard, whitish metal similar to platinum, is [#permalink]

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22 May 2011, 11:33
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Iridium, a hard, whitish metal similar to platinum, is extremely rare on Earth. Extremely high concentrations of iridium on Earth result
from only two scenarios: massive volcanic eruptions that release iridium from deep within the Earth and meteorites that shower down on Earth from space. When scientists found concentrations of iridium 30 times higher than normal in rock stratum from 65 million years
ago, they concluded that a massive meteor or comet hit the Earth and caused the massive extinction of the dinosaurs.

Which of the following, if true, most strongly supports the scientist’s conclusion?

A. Volcanoes massive enough to generate high concentrations of iridium are very rare.
B. Massive volcanic eruptions occurred frequently 80 million years ago.
C. Most scientists support the hypothesis that a cosmic impact wiped out the dinosaurs.
D. The massive extinction that occurred 70 million years ago killed not only the dinosaurs but also 70 percent of all life on Earth.
E. A comet struck the earth some 120 million years ago, but no widespread extinction occurred.

I think that C supports the conclusion better than B, which is the right answer. I am placing the question before this forum for moot so that I can learn flaws in my thought, if any.

Source: TMH's verbal workbook.

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[Reveal] Spoiler: OA

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Re: Iridium from meteors and comets: Need help [#permalink]

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22 May 2011, 12:44
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retro wrote:
Iridium, a hard, whitish metal similar to platinum, is extremely rare on Earth. Extremely high concentrations of iridium on Earth result
from only two scenarios: massive volcanic eruptions that release iridium from deep within the Earth and meteorites that shower down on Earth from space. When scientists found concentrations of iridium 30 times higher than normal in rock stratum from 65 million years
ago, they concluded that a massive meteor or comet hit the Earth and caused the massive extinction of the dinosaurs.

Which of the following, if true, most strongly supports the scientist’s conclusion?

A. Volcanoes massive enough to generate high concentrations of iridium are very rare.
B. Massive volcanic eruptions occurred frequently 80 million years ago.
C. Most scientists support the hypothesis that a cosmic impact wiped out the dinosaurs.
D. The massive extinction that occurred 70 million years ago killed not only the dinosaurs but also 70 percent of all life on Earth.
E. A comet struck the earth some 120 million years ago, but no widespread extinction occurred.

I think that C supports the conclusion better than B, which is the right answer. I am placing the question before this forum for moot so that I can learn flaws in my thought, if any.

Source: TMH's verbal workbook.

Regards
Rahul.

I thought it should be "A".

Conclusion:
The meteorite shower is the cause of the dinosaurs' extinction.

The scientists associated high concentration with meteorite shower and meteorite shower with extinction. But, there is no guarantee that high concentration of iridium was indeed due to meteorite shower and not volcanic eruptions.

A- clears the confusion that such high concentration can't be created by eruptions leaving us with only one choice for iridium concentration i.e. meteorite shower.

C- can be another possibility but using the word "cosmic impact" is too broad. Who knows if other scientists hypothesized that the extinction was due to ultraviolet rays(just in case there was no ozone then). Thus, a pure hypothesis by other scientists won't make this argument too strong.

Ans: "A"

But, on a second thought; the word "rare" in A is not too strong. Rare doesn't mean non-existential. Thus, the extinction may have been caused by volcanic eruption.

C becomes the strongest support.

Ans: "C"

"B" actually weakens the argument in a sense and is strict no-no.
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Re: Iridium from meteors and comets: Need help [#permalink]

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22 May 2011, 12:54
Fluke,

I could not get your final conclusion. What exactly are you converging on? A, B, C, D or E?

Rgds
Rahul
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Re: Iridium from meteors and comets: Need help [#permalink]

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22 May 2011, 12:58
retro wrote:
Fluke,

I could not get your final conclusion. What exactly are you converging on? A, B, C, D or E?

Rgds
Rahul

"C"
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Re: Iridium from meteors and comets: Need help [#permalink]

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22 May 2011, 14:49
Somewhere i also feel it should be C...
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Re: Iridium from meteors and comets: Need help [#permalink]

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22 May 2011, 19:47
There is a slight reasoning gap in the argument. It is between the two methods mentioned and the scientist picking up one of the methods for the conclusion.

Hence a supporter answer choice is required here that fills the gap in the reasoning.

A defender answer choice eliminating the 2nd method. Not an answer option.

B This is a sense can neither be related to the argument nor it supports the conclusion. It in fact weakens the conclusion. POE.

C gives a reason filling the gap in the reasoning mentioned above in the analysis. Crystal choice.

D and E are out of scope and hyperbole answer choices. POE.

C is clean here.
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Re: Iridium from meteors and comets: Need help [#permalink]

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22 May 2011, 21:08
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Here is the explanation provided by the guide:

Answer: B. This is a strengthen question. Its conclusion and premises are:
Premises: (1) Extremely high concentrations of iridium on Earth result from only two scenarios: massive volcanic eruptions that release iridium from deep within the Earth and meteorites that shower down on Earth from space. (2) Scientists found concentrations of iridium 30 times higher than normal in rock stratum from 65 million years ago.
Conclusion: A massive meteor or comet hit the Earth and caused the mass extinction of the dinosaurs.

According to the premises, there are two possible causes of high iridium levels. But the conclusion states that one of the causes—a meteor— was definitely the culprit. So the assumption must be that there was not a volcanic eruption that caused the extinction. Once again, you have a causal argument, but now you are going to strengthen it. In order to do so, you should look for answers that rule out other possible causes. Choice B strengthens the argument by showing that volcanic eruptions occurred frequently before the extinction, but the dinosaurs continued to live. Thus, it is unlikely that the extinction was caused by a volcano and more likely that a meteor caused it. Choice A doesn’t go far enough. Even if the volcanoes are rare, the extinction could have been caused by just one eruption. Choice C doesn’t strengthen the argument. Other scientists’ support of the hypothesis doesn’t address the connection between the conclusion and the premise. Choice D has nothing to do with the argument, while choice E weakens the argument by indicating that a previous comet strike did not lead to an extinction.

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Re: Iridium from meteors and comets: Need help [#permalink]

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24 May 2011, 09:49
retro wrote:
Here is the explanation provided by the guide:

Answer: B. This is a strengthen question. Its conclusion and premises are:
Premises: (1) Extremely high concentrations of iridium on Earth result from only two scenarios: massive volcanic eruptions that release iridium from deep within the Earth and meteorites that shower down on Earth from space. (2) Scientists found concentrations of iridium 30 times higher than normal in rock stratum from 65 million years ago.
Conclusion: A massive meteor or comet hit the Earth and caused the mass extinction of the dinosaurs.

According to the premises, there are two possible causes of high iridium levels. But the conclusion states that one of the causes—a meteor— was definitely the culprit. So the assumption must be that there was not a volcanic eruption that caused the extinction. Once again, you have a causal argument, but now you are going to strengthen it. In order to do so, you should look for answers that rule out other possible causes. Choice B strengthens the argument by showing that volcanic eruptions occurred frequently before the extinction, but the dinosaurs continued to live. Thus, it is unlikely that the extinction was caused by a volcano and more likely that a meteor caused it. Choice A doesn’t go far enough. Even if the volcanoes are rare, the extinction could have been caused by just one eruption. Choice C doesn’t strengthen the argument. Other scientists’ support of the hypothesis doesn’t address the connection between the conclusion and the premise. Choice D has nothing to do with the argument, while choice E weakens the argument by indicating that a previous comet strike did not lead to an extinction.

dear retro
even I couldn't get it how come the author is supporting the answer.........
may be fluke can help us......
I am sure that if this question would have appear on GMAT
i would have ruined my score further...
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Re: Iridium from meteors and comets: Need help [#permalink]

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24 May 2011, 20:39
Quote:
dear retro
even I couldn't get it how come the author is supporting the answer.........
may be fluke can help us......
I am sure that if this question would have appear on GMAT
i would have ruined my score further...

Hehe.. we are in the same boat, bloke.

Regards
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Re: Iridium from meteors and comets: Need help [#permalink]

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05 Aug 2011, 19:33
What's the source?

I, too, am going with $$A$$. $$B$$ does not strengthen the conclusion. $$A$$ leads us to believe that it probably wasn't the volcano eruption and more likely a massive meteor or comet that caused the increased iridium that coincides with the massive extinction of the dinosaurs.
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Re: Iridium from meteors and comets: Need help [#permalink]

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06 Aug 2011, 14:02
Notice that in the conclusion, the author has introduced another effect, 'extinction of dinosaurs'. Why?
Know this' why', and 50% job is done. The only reason from the context seems to be introduction of a layer of ambiguity to make the stimulus complex.
The other 50% is the elimination of this ambiguity. Choice 'b' shores up the implication that only the meteorite could have caused this extinction, and hence it is sufficient to remove the ambiguity.

meteorite -> extinction <-volcanic eruption
Choice 'c' is a close one. It does increases the weight of the causal link, 'meteorite -> extinction', but doesn't eliminate 'volcanic eruption ->extinction' link, the very cause of ambiguity.
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Re: Iridium, a hard, whitish metal similar to platinum, is [#permalink]

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26 Dec 2011, 06:20
I think this is too far a leap to be taken to reach the conclusion. Is this a regular GMAT-like question?

Even I thought the answer would be either A or C. B was totally unexpected.
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Re: Iridium, a hard, whitish metal similar to platinum, is [#permalink]

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26 Dec 2011, 10:36
We need to conclude that only meteor shower can bring that much of iridium 65 million year ago and not volcanic eruption.
And due to that dinosaurs got extinct
A does not prove this theory
B ok volcanic eruption was there 80 million back but no point in discussing for activity happened 65 million year ago
C possible yes they agree that cosmic activity was there
D and E has nothing to do with the point.

So C or B
B as no volcano happened in 65th year so it must be meteor shower
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Re: Iridium, a hard, whitish metal similar to platinum, is [#permalink]

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24 Jan 2012, 22:12
IMO A. But i'm utterly confused.
The explanation provided by the guide seems to give more weight to the cause of extinction of dinosaurs than to the cause of high iridium levels.
B. Massive volcanic eruptions occurred frequently 80 million years ago. the massive volcanic eruptions may have caused high iridium levels, but the explanation doesn't seem to care about that. It says, if massive eruption were frequent enough(80m years ago) and the dinosaurs were still not extinct(65m years ago), then the eruptions would not have caused the extinction.
Not sure which to give more importance to: the high levels of iridium or the extinction of dinosaurs
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Re: Iridium, a hard, whitish metal similar to platinum, is [#permalink]

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25 Jan 2012, 00:48
IMO C, but after reading the explaination it does make sense to go with B. Even though i would have never considered it before.
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Re: Iridium, a hard, whitish metal similar to platinum, is [#permalink]

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25 Jan 2012, 04:23
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Re: Iridium, a hard, whitish metal similar to platinum, is [#permalink]

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24 Apr 2012, 08:22
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Not a well-framed question but decent practice nonetheless.

Worth noting that even the hardest actual GMAC questions leave you somehow satisfied after reading the explanations/rationale for the correct answer--this particular question doesn't.

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Re: Iridium, a hard, whitish metal similar to platinum, is [#permalink]

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28 Feb 2013, 19:21
P1: Two causes

1. Volcanoes
2. Meteorites/Comets = > Iridium

P2: -65 million yrs , iridium was 30 times the normal

C: M/C => Dinosaurs extinction

Now B Says ,Massive volcanic eruptions occurred frequently 80 million years ago.Moreover,nowhere it is mentioned that they were infrequent (-65) million years.

A. Volcanoes massive enough to generate high concentrations of iridium are very rare.
B. Massive volcanic eruptions occurred frequently 80 million years ago.
C. Most scientists support the hypothesis that a cosmic impact wiped out the dinosaurs.
D. The massive extinction that occurred 70 million years ago killed not only the dinosaurs but also 70 percent of all life on Earth.
E. A comet struck the earth some 120 million years ago, but no widespread extinction occurred.

Poorly framed question

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Re: Iridium, a hard, whitish metal similar to platinum, is [#permalink]

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28 Feb 2013, 20:41
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targetgmatchotu wrote:
P1: Two causes

1. Volcanoes
2. Meteorites/Comets = > Iridium

P2: -65 million yrs , iridium was 30 times the normal

C: M/C => Dinosaurs extinction

Now B Says ,Massive volcanic eruptions occurred frequently 80 million years ago.Moreover,nowhere it is mentioned that they were infrequent (-65) million years.

A. Volcanoes massive enough to generate high concentrations of iridium are very rare.
B. Massive volcanic eruptions occurred frequently 80 million years ago.
C. Most scientists support the hypothesis that a cosmic impact wiped out the dinosaurs.
D. The massive extinction that occurred 70 million years ago killed not only the dinosaurs but also 70 percent of all life on Earth.
E. A comet struck the earth some 120 million years ago, but no widespread extinction occurred.

Poorly framed question

The OA is a little debatable but not very much.
(C) is certainly not in the running. Just because other people say it, something doesn't become true. You need facts. Most scientists supporting the hypothesis is not a fact that will help me believe the hypothesis. The reason why most scientists support it, might.
(D) and (E) are irrelevant.

So it comes down to:
A. Volcanoes massive enough to generate high concentrations of iridium are very rare.
B. Massive volcanic eruptions occurred frequently 80 million years ago.

Both support the conclusion to an extent.
In (A), volcanoes massive enough to generate high concentrations of iridium are rare, not impossible. There could have been one 65 million yrs ago. Hence, it doesn't strengthen our belief in a comet/meteor much.
In (B), massive volcanic eruptions occuring frequently through Earth's history while dinosaurs lived doesn't imply that there couldn't have been an especially huge one which wiped out the dinosaurs. But it does make comet/meteor theory more probable.

Look at the argument again - two things cause concentration of iridium - volcanoes and meteors
Volcanoes occured frequently while dinosaurs lived on Earth. Chances are that an activity which was not usual wiped out dinosaurs. Since dinosaurs were wiped out 65 million yrs ago and there was iridium concentration in rocks which are from 65 million yrs ago, it makes it more likely that a meteor wiped out dinosaurs.
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Re: Iridium, a hard, whitish metal similar to platinum, is [#permalink]

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27 Oct 2013, 10:44
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Karishma,

Option B comes somewhat closer, but B has flaws:
1. Do we know when for how long dinosaurs existed?
2. 80m years ago meteoric showers were frequent but is that anyhow supports dinosaurs to be killed?
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Re: Iridium, a hard, whitish metal similar to platinum, is   [#permalink] 27 Oct 2013, 10:44

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