Charcoal from a hearth site in Colorado, 2,000 miles south o

[JbhB682]

Charcoal from a hearth site in Colorado, 2,000 miles south of Alaska, is known to be 11,200 years old. Researchers reasoned that, since glaciers prevented human migration south from the Alaska-Siberia land bridge between 18,000 and 11,000 years ago, humans must have come to the Americas more than 18,000 years ago.

Which of the following pieces of new evidence would cast doubt on the conclusion drawn above?

(A) Using new radiocarbon dating techniques, it was determined that the charcoal from the Colorado site was at least 11,400 years old.

(B) Another campsite was found in New Mexico with remains dated at 16,000 years old.

(C) A computer simulation of glacial activity showed that it would already have been impossible for humans to travel south overland from Alaska 18,500 years ago.

(D) Using new radiocarbon dating techniques, it was proved that an ice-free corridor allowed passage south from the Alaska-Siberia land bridge at least 11,400 years ago.

(E) Studies of various other hunting-gathering populations showed convincingly that, once the glaciers allowed passage, humans could have migrated from Alaska to Colorado in about 20 years.

OA : D
Source : GMAT prep

[JbhB682]

Link :
https://ibb.co/7bc0gHC

[JbhB682]

Hello experts - question on the OA

I thought the OA stated the premise (marked in red color) was out right false.

Premise : migration CANNOT take place 18,000 years ago to 11,000 years ago
OA : D -- actually migration DID take place 11,400 years ago and before.

This is a strange OA because we are not allowed to question the premise (in red)

Thoughts ?

[TiffanyB]

Hello JbhB682,

Hello experts - question on the OA

I thought the OA stated the premise (marked in red color) was out right false.

It's more helpful to think that the answer choices may WEAKEN certain premises or provide alternative explanations. People used to believe that the world was flat, but then we received more information via observations and research. Now we believe accept a different truth.

When you're reading CR questions, you believe what is in the original argument, but you also keep in mind that there may be gaps in understanding or assumptions that the author is making.

In this case, the researchers were assuming that while the glaciers were moving from 18,000 to 11,000 years ago, there was NO possible means of traveling through that area.

Answer choice (D) illustrates that SOME travel may actually have been possible.

Premise : migration CANNOT take place 18,000 years ago to 11,000 years ago
OA : D -- actually migration DID take place 11,400 years ago and before.

This is a strange OA because we are not allowed to question the premise (in red)

Thoughts ?

Again, I would frame this as getting additional information that changes how you understand the original information provided.

[JbhB682]

Thank you so much Tiffany for responding.

I think what you are saying is

-- Per the premise (in red) : NO TRAVEL was possible (because of the glaciers)
-- Per the D -- Actually based on new evidence - 'Some travel' was possible (even though the glaciers were present)

Do you think this kind of 'weakening ' is acceptable only because of the *specific type** of question stem (i.e - the question stem -- mention - 'look out for new evidence') ?

Which of the following pieces of new evidencewould cast doubt on the conclusion drawn above?

Its because of this "new evidence" mentioned in the question stem -- we are allowed to challenge the premises ?

[JbhB682]

^^ Had the question stem been the 'classic' type of weaken questions stem

(i) If true, which of the following most calls into question the conclusion above?
(ii) Which of the following, if true, most seriously weakens the argument?

Would you still select D ?

I am not sure i would..... I would be looking for weakeners like
-- earlier than 18,000 years ago : it would not be possible for humans to come south of the border to America because of Humans had not learnt to travel for such long distances

-- glaciers made it IMPOSSIBLE for humans to travel PRIOR to 18,000 years ago as well

[Whit Garner]

^^ Had the question stem been the 'classic' type of weaken questions stem, Would you still select D ?

I am not sure i would..... I would be looking for weakeners like
-- earlier than 18,000 years ago : it would not be possible for humans to come south of the border to America because of Humans had not learnt to travel for such long distances
-- glaciers made it IMPOSSIBLE for humans to travel PRIOR to 18,000 years ago as well

Hi! Great question. While it might seem *unique* that this question specifically says "new pieces of evidence," but you want to expect that any Strengthen / Weaken answer is likely to present new information.

For me, I'd have read "what would weaken" and my mind would have gone to the following:
1. They said no travel south... was there another way?
2. Were they wrong about the dates?
3. Were they wrong about it being impassable?

(C) Would have survived through the first round of eliminations for sure! However, it brings up a year that pre-dates the window in question AND well predates the time we're seeing hearth sites in Colorado. (C) is also a computer simulation (so still just a hypothesis). My question #2 is still really valid here.

(D) gives me a hole for question #3 to exploit that is really close to the year we're seeing charcoal AND they say proved based on actual evidence (not just a simulation).