Climate researchers examined sediments in a cave in Region Z, which

Question

Climate researchers examined sediments in a cave in Region Z, which now has a temperate climate, and they found arctic lemming bones in a buried layer corresponding to about 14,000 B.C. Arctic lemmings are typical of arctic climates and are unlikely to have changed their adaptation for temperature over a period as short as 16,000 years. So Region Z probably had an arctic climate around 14,000 B.C.

Which of the following is an assumption that the argument requires?

A. Arctic lemmings were, around 14,000 B.C., well adapted to the climate of the region where the bones were found. - ok.

B. Adjacent layers did not contain bones of arctic lemmings. - out of scope.

C. Temperature shifts between arctic and temperate climates are common over the long term. - common or not common is out of scope.

D. No bones of warm-weather animals from any period were found in nearby caves in Region Z. - "Any period" is out of scope, which is "about 14,000 BC"

E. The bones were from a species of lemming that was probably not well adapted for survival in the region where their bones were found. - weakener.

MartyMurray · Accepted Answer

Climate researchers examined sediments in a cave in Region Z, which now has a temperate climate, and they found arctic lemming bones in a buried layer corresponding to about 14,000 B.C. Arctic lemmings are typical of arctic climates and are unlikely to have changed their adaptation for temperature over a period as short as 16,000 years. So, Region Z probably had an arctic climate around 14,000 B.C.

The conclusion of the argument is the following:

Region Z probably had an arctic climate around 14,000 B.C.

The support for the conclusion is the following:

Climate researchers ... found arctic lemming bones in a buried layer corresponding to about 14,000 B.C.

Arctic lemmings are typical of arctic climates and are unlikely to have changed their adaptation for temperature over a period as short as 16,000 years.

We see that the argument goes from evidence involving the climate arctic lemmings are adapted to to a conclusion about the climate of Region Z around 14,000 B.C.

Which of the following is an assumption that the argument requires?

This is an Assumption question. So, the correct answer will be the one that's necessary for the evidence to effectively support the conclusion.

A. Arctic lemmings were, around 14,000 B.C., well adapted to the climate of the region where the bones were found.

As we saw above, the argument goes from the evidence that bones of lemmings were found in a layer corresponding to the time around 14,000 B.C. and that lemmings are adapted to arctic climates to the conclusion that Region Z had an arctic climate around 14,000 B.C.

For the evidence to effectively support the conclusion, the adaptation of lemmings to arctic climates must be connected to the climate in Region Z around 14,000 B.C.

So, for the argument to work, the assumption that arctic lemmings were, around 14,000 B.C., well adapted to the climate of Region Z is necessary.

After all, if lemmings were NOT well adapted to that climate, then the fact that lemming bones were found in Region Z would not be a reason to believe that Region Z had an arctic climate. After all, in that case, lemmings could have been adapted to an arctic climate while Region Z had a different kind of climate to which the lemmings were not well adapted.

So, this choice states an assumption upon which the argument relies.

Keep.

B. Adjacent layers did not contain bones of arctic lemmings.

The conclusion of the argument is that Region Z DID have an arctic climate around 14,000 B.C. The conclusion is not that Region Z DID NOT have an artic climate before or after around 14,000 B.C.

So, it's not necessary to assume that adjacent layers did not contain bones of arctic lemmings. After all, regardless of whether adjacent layers contained bones of artic lemmings, Region Z could have had an artic climate at the time corresponding to the layer examined.

Eliminate.

C. Temperature shifts between arctic and temperate climates are common over the long term.

The argument's conclusion is basically that there was ONE temperature shift, a shift from an artic climate that existed around 14,000 B.C. to a temperate climate exisiting now.

To conclude that one temperature shift occurred does not require assuming that such temperature shifts are "common." After all, even if such temperature shifts are NOT common, one such shift could have occurred.

Eliminate.

D. No bones of warm-weather animals from any period were found in nearby caves in Region Z.

This choice is tricky because the presence of bones of warm-weather animals could seem to disprove the conclusion that Region Z had an artic climate. So, for the argument to work, it could seem necessary to assume that no bones of warm-weather animals were found in the area.

What we need to notice, however, is that the conclusion of the argument is about a specific time period, the time period around 14,000 B.C. So, as long as no bones of warm-weather animals are tied to that period, the argument works.

Thus, the assumption that no bones of warm-weather animals from ANY period were found in nearby caves in Region Z is not necessary. After all, even if bones of warm-weather animals from a period other than around 14,000 B.C. were found, the argument could still work.

Eliminate.

E. The bones were from a species of lemming that was probably not well adapted for survival in the region where their bones were found.

The reasoning of the argument is basically that, since lemmings are adapted to arctic climates, Region Z had an arctic climate.

So, this choice is an opposite trap that casts doubt on rather than supports the conclusion.

After all, if the species of lemming whose bones were found was probably not well adapted for survival in Region Z, then if the lemmings were adapted for an artic climate, then Region Z probably did not have an artic climate.

Eliminate.

Correct answer:  A

HarshavardhanR · Answer

My two cents   
 My understanding of the argument:

- There is a region Z. This region has a  temperate  (mild - not too hot,  not too cold ) climate  at present  .
- Certain climate researchers studied  sediments  (layers of soil) in a cave in region Z.
- They found bones of a bird called  arctic  lemming in a  buried  layer. This layer of sediment corresponds to 14000 BC (i.e.,  this soil is from 16000 years ago ). 
- The above suggests that  the arctic lemming was present in this region at least at some point in and around 14000 BC.

Sidenote:   With the passage of time, layers of soil typically get deposited on top of current soil. So, typically, as one goes deeper into the layers of soil, they reach soil layers that are more ancient than the upper layers.

- Arctic lemmings exist even today (Note "are typical of", "belong", etc.). They belong to arctic climates ( very cold ).
- It is not likely that these birds changed their adaptation for temperature in such a short span as 16000 years.
-  What the above essentially means  ->  We know that arctic lemmings naturally belong to cold arctic climates today; Even 16000 years ago, in 14000 BC, they had the adaptations to thrive in cold climates only. It is not that in 14000 BC, the bird was well suited for tropical climates (say) and today, in a span of 16000 years, it has become an arctic bird suited for uber cold climates - n ope.

-  Conclusion  -> So, this  region Z probably had an arctic (very cold) climate around 14000 BC. 
-  Logic, in brief  -> 
 Artic lemming was definitely present in region Z around 14000 BC. This bird is presently built for very cold climates. This bird could not have been well suited for any other climate within a span of 16000 years. So, this bird was clearly suited for very cold climates only, even in 14000 BC. This must mean that region Z, where the bird was present in 14000 BC, probably had an arctic climate in 14000 BC.

Analysis 
- The arctic lemming bird, today, is well suited (has the adaptations) for cold climates. 
- As per the argument, the bird, even in 14000 BC, was a cold-climate bird.

Great. But there is a logical gap between  being present in 14000 BC in region Z (as the bone remains confirm)  and  thriving/surviving thanks to being well-suited for the climate in that place at that time.

For instance :  What if  ->

- Around 14000 BC, region Z had a tropical (hot!) climate, and
- the bones found recently were of arctic lemming birds that died because they could not adapt to the hot climate.

It is possible that region Z did not have the suited climate for these birds around 14000 BC. It is possible that the arctic lemming birds in that region died during that time, given they did not have the needed adaptations to survive in that weather. And it is these birds' boney remains that were recently discovered by climate researchers.

In such a scenario, can the author still make the stated claim? No.

The author is  assuming  that the arctic lemming birds that existed in 14000 BC in region Z must have been well-suited to live in the climate prevalent at that time in the region.

This, I think, is the reasoning behind choice A.

Hope this helps.
___
Harsha

Rucha.Shukla · Answer

Based on following lines from passage:

Arctic lemmings are typical of arctic climates and are unlikely to have changed their adaptation for temperature over a period as short as 16,000 years. So Region Z probably had an arctic climate around 14,000 B.C

Is E the answer?

Posted from my mobile device

saurabhmishrano1 · Answer

A. Arctic lemmings were, around 14,000 B.C., well adapted to the climate of the region where the bones were found.

- This assumption is necessary for the argument because it establishes the suitability of the climate for arctic lemmings around 14,000 B.C. If the lemmings were not adapted to the climate, their presence would not provide evidence of the climate conditions at that time.
   -  Example : Suppose further analysis of the lemming bones reveals specific physiological adaptations consistent with cold climates, such as thick fur or specialized metabolism. This information would support the assumption that the lemmings were well adapted to the climate of the region during the specified time period.

B. Adjacent layers did not contain bones of arctic lemmings.

- This assumption is not explicitly required for the argument because the absence of arctic lemming bones in adjacent layers does not necessarily impact the conclusion about the climate around 14,000 B.C.
   -  Example : Even if adjacent layers did contain arctic lemming bones, the presence of such bones in a specific layer corresponding to 14,000 B.C. still provides evidence of the climate at that time, regardless of the absence or presence of lemming bones in adjacent layers.

C. Temperature shifts between arctic and temperate climates are common over the long term.

- This assumption is not necessary for the argument because the argument focuses on the specific climate conditions of Region Z around 14,000 B.C. Whether temperature shifts are common over the long term does not directly impact the conclusion about the climate at that specific time period.
   -  Example : Even if temperature shifts between arctic and temperate climates are common over the long term, it does not change the fact that arctic lemming bones were found in Region Z around 14,000 B.C., suggesting an arctic climate at that time.

D. No bones of warm-weather animals from any period were found in nearby caves in Region Z.

- This assumption is not necessary for the argument because the absence of bones from warm-weather animals in nearby caves does not directly relate to the evidence presented regarding arctic lemming bones in a specific layer of sediment.
   -  Example : Even if bones of warm-weather animals were found in nearby caves, it would not necessarily impact the conclusion drawn from the discovery of arctic lemming bones in a specific layer of sediment in Region Z.

E. The bones were from a species of lemming that was probably not well adapted for survival in the region where their bones were found. 
    - This assumption contradicts the argument's premise, which states that arctic lemmings are typical of arctic climates. Therefore, this assumption would weaken rather than strengthen the argument.
   -  Example : If it were assumed that the lemming bones belonged to a species not well adapted to arctic climates, it would cast doubt on the conclusion that Region Z had an arctic climate around 14,000 B.C.

Jayam12 · Answer

I don't understand why C is not the correct assumption. If shift in temperatures is not common in the long term, doesn't it defeat the conclusion that Region Z has an arctic climate. It is clearly mentioned that now this region has temperate climate. Then for sure we would need to assume that a shift in temperature is possible right?

MartyMurray need your help

MartyMurray  need your help

MartyMurray · Answer

Hi Jayam.

Look above at what you said. I bolded two parts of it.

Notice that those two parts are not  the same.

Yes, for the argument to work, "temperature shifts between arctic and temperate climates" must be "possible."

On the other hand, the argument still works even if they are not "common."

After all, we need such a shift to have occurred just once, not commonly, for the conclusion to be correct.

HardikA170 · Answer

@Bunuel Would appreciate an experts analysis on this one, thank you

Gemmie · Answer

1.   The argument states:  Arctic lemmings are suited for arctic climates and wouldn't adapt significantly in 16,000 years.
 2. They found:  Bones of arctic lemmings in a layer dated to 14,000 B.C. in Region Z (now temperate).
 3. They conclude:  Region Z must have had an arctic climate around 14,000 B.C.

=> Why is this conclusion made?  Because if the first two statements are true, then the only logical explanation for finding arctic lemming bones is that the climate back then was suited to them, which means arctic.

=> What assumption is required for this conclusion to hold?  The argument assumes that the lemmings found were indeed adapted to the climate where they were found (Region Z at 14,000 B.C.). If the lemmings could survive in temperate climates as well, then their presence wouldn't necessarily indicate an arctic past.

So, the key assumption is:  A. Arctic lemmings were, around 14,000 B.C., well adapted to the climate of the region where the bones were found.

gmatstudent20 · Answer

deleted

egmat · Answer

Watch this solution to see how to tackle a challenging Critical Reasoning question that tests your ability to identify and evaluate factors crucial for the conclusion's validity.
Learn to distinguish between relevant and irrelevant information, and see how to quickly pinpoint the assumptions underlying the argument.
This approach will help you save valuable time in the exam by focusing on the core elements that strengthen or weaken the conclusion.

https://www.youtube.com/watch?v=vu4jgZrMUf0

Can you spot the key assumption before it's revealed in the explanation?

Raman109 · Answer

Climate researchers examined sediments in a cave in Region Z, which now has a temperate climate, and they found arctic lemming bones in a buried layer corresponding to about 14,000 B.C. Arctic lemmings are typical of arctic climates and are unlikely to have changed their adaptation for temperature over a period as short as 16,000 years. So Region Z probably had an arctic climate around 14,000 B.C.

Which of the following is an assumption that the argument requires?

A. Arctic lemmings were, around 14,000 B.C., well adapted to the climate of the region where the bones were found. - ok.

B. Adjacent layers did not contain bones of arctic lemmings. - out of scope.

C. Temperature shifts between arctic and temperate climates are common over the long term. - common or not common is out of scope.

D. No bones of warm-weather animals from any period were found in nearby caves in Region Z. - "Any period" is out of scope, which is "about 14,000 BC"

E. The bones were from a species of lemming that was probably not well adapted for survival in the region where their bones were found. - weakener.

chiplesschap · Answer

I eliminated C for the wrong reasons. I thought hey the answer choice says 'over the long term' but the question stem says 16,000 years is a 'short period'. This contradiction sort of me put me off C. But now that I've read the explanations, it makes sense. Thank you!

VerbalBot · Answer

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Climate researchers examined sediments in a cave in Region Z, which

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Climate researchers examined sediments in a cave in Region Z, which

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