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by Ozlemg » Wed Aug 03, 2011 4:00 am
Most archaeologists have held that people first reached the Americas less than 20,000 years ago by crossing a land bridge into North America. But recent discoveries of human shelters in South America dating from 32,000 years ago have led researchers to speculate that people arrived in South America first, after voyaging across the Pacific, and then spread northward.

Which of the following, if it were discovered, would be pertinent evidence against the speculation above?

A. A rock shelter near Pittsburgh, Pennsylvania, contains evidence of use by human beings 19,000 years ago.
B. Some North American sites of human habitation predate any sites found in South America.
C. The climate is warmer at the 32,000-year-old South American site than at the oldest known North American site.
D. The site in South America that was occupied 32,000 years ago was continuously occupied until 6,000 years ago.
E. The last Ice Age, between 11,500 and 20,000 years ago, considerably lowered worldwide sea levels.

What do you think about [spoiler]E?[/spoiler] Is it wrong because it does not guarantee (not sufficient) that people crossed to NA btw 11.500 and 20.000.
OA B
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by GmatKiss » Wed Aug 03, 2011 4:12 am
E does not qualify!

Given: south American site is found to be 32,000 years old.

E: 11,500 - 20,000- does not mean NA was found before SA.
B: Clear, direct- says NA has sites predating SA sites, means beyond (older than) 32,000 years.
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by BlindVision » Wed Aug 03, 2011 1:00 pm
Ozlemg wrote:Most archaeologists have held that people first reached the Americas less than 20,000 years ago by crossing a land bridge into North America. But recent discoveries of human shelters in South America dating from 32,000 years ago have led researchers to speculate that people arrived in South America first, after voyaging across the Pacific, and then spread northward.

Which of the following, if it were discovered, would be pertinent evidence against the speculation above?

A. A rock shelter near Pittsburgh, Pennsylvania, contains evidence of use by human beings 19,000 years ago.
B. Some North American sites of human habitation predate any sites found in South America.
C. The climate is warmer at the 32,000-year-old South American site than at the oldest known North American site.
D. The site in South America that was occupied 32,000 years ago was continuously occupied until 6,000 years ago.
E. The last Ice Age, between 11,500 and 20,000 years ago, considerably lowered worldwide sea levels.

What do you think about [spoiler]E?[/spoiler] Is it wrong because it does not guarantee (not sufficient) that people crossed to NA btw 11.500 and 20.000.
OA B
E can be ruled out because between 11,500 and 20,000 years ago...considerably lowered worldwide sea levels, which means that people could have reached the Americas less than 20,000 years ago by crossing a land bridge into North America. This would support the speculation instead of against it.
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by mrigank_bhushan » Tue Feb 04, 2014 7:09 am
i was going through some material today and i found this question a little warped. The answer choice B actually states a fact which is contradicting to the premise. The premise says the migration happended less than 20 thousand years ago, whereas the answer choice suggests habitation in the N. Americas before 32 thousand years(say 35 thousand years). I dont know whether this tactical error is something which we might encounter in the real exam, where an answer choice maybe correct even if its factually contradictory to the premise.

Also why cant C be an answer. A warmer climate made a solid habitat for the people who couldnt move northwards because the weather wasnt suitable for them and hence the speculation stands flawed. Why are we ignoring this logic?
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by Abhishek009 » Tue Feb 04, 2014 9:39 am
Ozlemg wrote:Most archaeologists have held that people first reached the Americas less than 20,000 years ago by crossing a land bridge into North America. But recent discoveries of human shelters in South America dating from 32,000 years ago have led researchers to speculate that people arrived in South America first, after voyaging across the Pacific, and then spread northward.
Earlier- America was reached by crossing land Bridge into North America 20,000 Yrs ago.

Now - Human Shelters in South America dating 32,000 Yrs back suggests people arrive here first and spread westwards.

Which of the following, if it were discovered, would be pertinent evidence against the speculation above?

The speculation arrived here is that people spread northwards from South America.

A. A rock shelter near Pittsburgh, Pennsylvania, contains evidence of use by human beings 19,000 years ago.

Irrelevant.

B. Some North American sites of human habitation predate any sites found in South America.

If there is evidence of Human habitation before those found in South America then the recent discovery can be challenged. - This seems good , lets check other options.

C. The climate is warmer at the 32,000-year-old South American site than at the oldest known North American site.

Not relevant to the discussion.

D. The site in South America that was occupied 32,000 years ago was continuously occupied until 6,000 years ago.

Not useful to challenge the recent findings.

E. The last Ice Age, between 11,500 and 20,000 years ago, considerably lowered worldwide sea levels.

Absolutely out of scope of discussion...


IMO (B) seems the best , it directly challenges the reasoning ...
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by David@VeritasPrep » Tue Feb 04, 2014 11:25 am
mrigank_bhushan: to answer your question.

Abhishek009 has given a good explanation above. I just want to point out that what you say in this quote is not actually true:
The answer choice B actually states a fact which is contradicting to the premise. The premise says the migration happened less than 20 thousand years ago, whereas the answer choice suggests habitation in the N. Americas before 32 thousand years(say 35 thousand years). I dont know whether this tactical error is something which we might encounter in the real exam, where an answer choice maybe correct even if its factually contradictory to the premise.
You see the actual premise says, "Most archaeologists have held that people first reached the Americas less than 20,000 years ago by crossing a land bridge into North America." This is followed by the word "but"...THIS IS A CLASSIC SETUP ON THE GMAT. The author of the stimulus is not saying that the migration happened less than 20 thousand years ago. He or she is saying that someone (in this case archaeologists) believe it. With the word "but" we have a negation and we see that the author of the stimulus does not take the belief as a fact and is indeed contradicting it immediately.

This type of stimulus occurs very frequently. From what I have seen at least 1 in 5 arguments have this negation. So be on the look out for it!

Here is another example, this one from the Veritas Critical Reasoning Book.

"Opponents of peat harvesting in this country argue that it would alter the ecological balance of our peat-rich wetlands and that, as a direct consequence of this, much of the country's water supply would be threatened with contamination. But this cannot be true, for in Ireland, where peat has been harvested for centuries, the water supply is not contaminated. We can safely proceed with the harvesting of peat."

Notice how the OPPONENTS argue that the water supply would be threatened and then the argument negates this with the "But this cannot be true."

Do not be confused with a fact that the argument (or the author of the argument) accepts and one that the argument states in order to refute it!

Hope it helps!
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