Samples from the floor of a rock shelter in Pennsylvania : GMAT Critical Reasoning (CR)
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# Samples from the floor of a rock shelter in Pennsylvania

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CEO
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Samples from the floor of a rock shelter in Pennsylvania [#permalink]

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14 Dec 2007, 23:46
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Samples from the floor of a rock shelter in Pennsylvania were dated by analyzing the carbon they contained. The dates assigned to samples associated with human activities formed a consistent series, beginning with the present and going back in time, a series that was correlated with the depth from which the samples came. The oldest and deepest sample was dated at 19,650 years before the present, plus or minus 2,400 years. Skeptic, viewing that date as too early and inconsistent with the accepted date of human migration into North America, suggested that the samples could have been contaminated by dissolved old carbon carried by percolating groundwater from nearby coal deposits.
Which one of the following considerations, if true, argues most strongly against the suggestion of the skeptics?

A. No likely mechanism of contamination involving percolating groundwater would have affected the deeper samples from the site without affecting the uppermost sample.

B. Not every application of the carbon-dating procedure has led to results that have been generally acceptable to scientists.

C. There is no evidence that people were using coal for fuel at any time when the deepest layer might have been laid down.

D. No sample in the series, when retested by the carbon-dating procedure, was assigned an earlier date than that assigned to a sample from a layer above it.

E. No North American site besides the one in Pennsylvania has ever yielded a sample to which the carbon-dating procedure assigned a date that was comparably ancient.

Plz include your reasoning. I swear I saw this before and gave my answer it is incorrect according to GMATTER.
If you have any questions
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15 Dec 2007, 09:27
A is the only one that makes sense to me.

The skeptics are saying that the sample was contaminated by percolating groundwater, if there is no likely mechanism of contamination this helps rule out their theory.

B: just because scientists haven't agreed with results in the past doesn't mean these are correct or incorrect

C: it doesn't matter whether they were using coal or not. groundwater carrying contaminates has nothing to do with use.

D. this could establish what happened when, but nothing to do with exactly how many years ago it occurred.

E. if anything this would help back up the skeptics. but even then it doesn't rule out the possibility, it just says it hasn't happened before.
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16 Dec 2007, 02:38
Very tricky.
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Trying hard to achieve something unachievable now....

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Re: CR- Carbon 14 Dating (long one) [#permalink]

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16 Dec 2007, 21:24
GMATBLACKBELT wrote:
Samples from the floor of a rock shelter in Pennsylvania were dated by analyzing the carbon they contained. The dates assigned to samples associated with human activities formed a consistent series, beginning with the present and going back in time, a series that was correlated with the depth from which the samples came. The oldest and deepest sample was dated at 19,650 years before the present, plus or minus 2,400 years. Skeptic, viewing that date as too early and inconsistent with the accepted date of human migration into North America, suggested that the samples could have been contaminated by dissolved old carbon carried by percolating groundwater from nearby coal deposits.
Which one of the following considerations, if true, argues most strongly against the suggestion of the skeptics?

A. No likely mechanism of contamination involving percolating groundwater would have affected the deeper samples from the site without affecting the uppermost sample.

B. Not every application of the carbon-dating procedure has led to results that have been generally acceptable to scientists.

C. There is no evidence that people were using coal for fuel at any time when the deepest layer might have been laid down.

D. No sample in the series, when retested by the carbon-dating procedure, was assigned an earlier date than that assigned to a sample from a layer above it.

E. No North American site besides the one in Pennsylvania has ever yielded a sample to which the carbon-dating procedure assigned a date that was comparably ancient.

Plz include your reasoning. I swear I saw this before and gave my answer it is incorrect according to GMATTER.

D
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16 Dec 2007, 23:07
I think answer is A? What is OA?
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Re: Samples from the floor of a rock shelter in Pennsylvania [#permalink]

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04 Jul 2012, 01:45

Per A "No likely mechanism of contamination involving percolating groundwater would have affected the deeper samples from the site without affecting the uppermost sample." - but this can also mean that the percolation resuted in contamination of both the upper and the bottom layers and thus the estimation could be wrong for all samples. how does this prove definitely that the percolation did not occur AT ALL ?

Thanks,
Shreya
Re: Samples from the floor of a rock shelter in Pennsylvania   [#permalink] 04 Jul 2012, 01:45
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