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Iridium

by reply2spg » Sat Jul 31, 2010 11:39 am
Source - McGraw-Hills (Conquering Gmat, Drill # 1, Q # 4)

Iridium, a hard, whitish metal similar to platinum, is extremely rare on Earth. extremely high concentrations of Iridium on Earth result from only 2 scenarios : massive volcanic eruptios 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 commet hit the earth and caused the massive extinction of the dinosaurs.

Which of the following, if true, most strongly supports the scientists conclusion?

1. Volcanos massive enough to generate high concentrations of iridium are very rare

2. massive volcanic erruptios occured frequently 80 million years ago.

3. Most scientists support the hypothesis that a cosmic impact wiped out the dinosaurs

4. The massive extinction that occured 70 million years ago killed not only the dinosaurs but also 70% of all life on the earth

5. A comet struck the earth some 20 million years ago, but no widespread extinction occured

OA later
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by sk818020 » Sat Jul 31, 2010 12:52 pm
I'm going to have to go with [spoiler]C[/spoiler], although I'm still not 100% on this one. Reasons are as follows:

1. This, in a way, weakens the argument because it gives further evidence that it is still possible that volcanoes did cause this high concentration of iridium.
2. We're not concerned with what happened 80 million years ago. This might be relevant if it talked about this being 65 million years ago. This is irrelevant.
3. I elected via process of elimination.
4. This would actually weaken the scientist conclusion because this question would give evidence that the extinction actually occurred 5 million years before the meteor hit.
5. Again, this is irrelevant because we're not concerned with what happened 20 million years ago.

Could you please confirm the OA?

Thanks,

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by reply2spg » Sat Jul 31, 2010 1:06 pm
Actually I was not convinced with any of the answer choices. When I saw OA, I was stumped.

Let's get some more replies for this, before I post OA
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by sk818020 » Sat Jul 31, 2010 1:53 pm
Agreed I think this is a poorly written question and I doubt you would see something like this on the GMAT. I looked up the answer and the OE and I don't like it either.

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by apex231 » Sat Jul 31, 2010 8:09 pm
A looks best of all. It strongly suggests that the high concentration of Iridium can be attributed to a meteorite/comet impact.

What's the OA and OE?
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by reply2spg » Sat Jul 31, 2010 8:35 pm
Can I post OA??
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by dream700 » Sat Jul 31, 2010 9:08 pm
IMO A

We are told that "extremely high concentrations of Iridium on Earth result from only 2 scenarios : massive volcanic eruptios that release Iridium from deep within the Earth and meteorites that shower down on Earth from space."

A explains that the high level of Iridium found can't be through volcanic eruption. Thus this contributes to the assumption that a meteorite or comet must have hit the Earth.

Hope this helps!

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by reply2spg » Sat Jul 31, 2010 9:10 pm
Guys OA is B for this....which is completely irrelevant to the passage. Can someone help me out to understand how B is correct?
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by neha.patni » Sun Aug 01, 2010 3:27 am
reply2spg wrote:Source - McGraw-Hills (Conquering Gmat, Drill # 1, Q # 4)

Iridium, a hard, whitish metal similar to platinum, is extremely rare on Earth. extremely high concentrations of Iridium on Earth result from only 2 scenarios : massive volcanic eruptios 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 commet hit the earth and caused the massive extinction of the dinosaurs.

Which of the following, if true, most strongly supports the scientists conclusion?

1. Volcanos massive enough to generate high concentrations of iridium are very rare

2. massive volcanic erruptios occured frequently 80 million years ago.

3. Most scientists support the hypothesis that a cosmic impact wiped out the dinosaurs

4. The massive extinction that occured 70 million years ago killed not only the dinosaurs but also 70% of all life on the earth

5. A comet struck the earth some 20 million years ago, but no widespread extinction occured

OA later
IMO C

How can it be B

When the conclusion is talking about the meteor impact as the cause of iridium and dinosaur extinction. A & B - Talk about volcanic eruptions.

D & E - not relevant.

Experts please help
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by Shawshank » Sun Aug 01, 2010 5:34 am
i think its between A and C

B is definitely wrong,,,,

IMO -- A
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by crackinggmat » Sun Aug 01, 2010 8:39 am
i dont trust mc graw ....i tried to study from mcgraw ...but didn,t like it ...many questions were not of gmat style....
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by selango » Sun Aug 01, 2010 10:30 am
The question aks us to provide additional support.

Extreme concentrations of Iridium-->Volcanic eruptions and Meteorites.

The argument provides one evidence supporting Meteortites.If there is another argument providing support to another cause(ie)Volcanic eruptions,then there ll be 2 causes supporting this evidence.

Hence B is the answer.

Still I may be wrong..Any thoughts?
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by diebeatsthegmat » Mon Aug 02, 2010 12:09 am
reply2spg wrote:Guys OA is B for this....which is completely irrelevant to the passage. Can someone help me out to understand how B is correct?
why is B correct? i chose D
A and E and C are out of scope
but B seems to be irrelevant? any explainations?
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by adi_800 » Sat Aug 14, 2010 9:41 pm
selango wrote:The question aks us to provide additional support.

Extreme concentrations of Iridium-->Volcanic eruptions and Meteorites.

The argument provides one evidence supporting Meteortites.If there is another argument providing support to another cause(ie)Volcanic eruptions,then there ll be 2 causes supporting this evidence.

Hence B is the answer.

Still I may be wrong..Any thoughts?
The argument has two causes of Iridium increasing...one is massive meteor or commet hit or volcano eruptions..
The author concludes that it is the massive meteor or commet hit that caused iridium increase and not volcano eruptions...

But B talks about massive volcanic eruptions and that too 80 million years ago...
How can then B support the conclusion..

It has to be C. as C tells that D extinction was due to (caused by) massive meteor and nothing else...
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by Ian Stewart » Sun Aug 15, 2010 11:06 am
This question doesn't make any sense, at least if the answer is B. It's hard to see why *anything* that happened 80 million years ago might be relevant here, since we're concerned about events only 65 million years ago (that's a 15 million year difference - not a short amount of time!).

To support the conclusion that the iridium is from a comet, and not from a volcano, we'd either need additional evidence that a comet struck the earth 65 million years ago, or information ruling out a volcano as the source. The only answer I find remotely justifiable is A; if volcanic eruptions are extremely rare, that makes it less likely that an eruption was the source of the iridium.

Still, I think it's a bad question. I'd strongly recommend working from higher quality materials for Verbal prep; there was another question posted here recently from the same source that also had serious issues.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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