Scientists analyzing air bubbles that had been trapped in Antarctic

Question

Scientists analyzing air bubbles that had been trapped in Antarctic ice during the Earth’s last ice age found that the ice-age atmosphere had contained unusually large amounts of ferrous material and surprisingly small amounts of carbon dioxide. One scientist noted that algae absorb carbon dioxide from the atmosphere. The scientist hypothesized that the ferrous material, which was contained in atmospheric dust, had promoted a great increase in the population of Antarctica algae such as diatoms.

Which one of the following, if true, would most seriously undermine the scientist’s hypothesis?

(A) Diatoms are a microscopic form of algae that has remained largely unchanged since the last ice age.

(B) Computer models suggest that a large increase in ferrous material today could greatly promote the growth of oceanic algae.

(C) The dust found in the air bubbles trapped in Antarctica ice contained other minerals in addition to the ferrous material.

(D) Sediment from the ocean floor near Antarctica reflects no increase, during the last ice age, in the rate at which the shells that diatoms leave when they die accumulated.

(E) Algae that currently grow in the oceans near Antarctica do not appear to be harmed by even a large increase in exposure to ferrous material.

fluke · Accepted Answer

Scientists analyzing air bubbles that had been trapped in Antarctic ice during the Earth’s last ice age found that the ice-age atmosphere had contained unusually large amounts of ferrous material and surprisingly small amounts of carbon dioxide. One scientist noted that algae absorb carbon dioxide from the atmosphere. The scientist hypothesized that the ferrous material, which was contained in atmospheric dust, had promoted a great increase in the population of Antarctica algae such as diatoms.

Bubble revealed that air in ice-age had high ferrous content and very little carbon-dioxide.
Hypothesis: Ferrous material increased algae, which in turn absorbed CO2 from atmosphere. This theory explains a possible reason for low CO2 level.

Which one of the following, if true, would most seriously undermine the scientist’s hypothesis?
 We need to weaken the hypothesis or prove it wrong.

A) Diatoms are a microscopic form of algae that has remained largely unchanged since the last ice age.
 This information actually helps to a certain extent in corroborating the hypothesis. Since Diatoms didn't change much, it still traps CO2 as it during the ice age. Thus, at least the information about the CO2 trapping property of diatoms is not baseless. However, this statement doesn't undermine the hypothesis. It is more like a standalone fact.

(B) Computer models suggest that a large increase in ferrous material today could greatly promote the growth of oceanic algae.
 Something true today may not have been true in the past, esp. in ice age when temperature was extreme. Furthermore, this only strengthens the hypothesis that ferrous material might have caused the increase in algae. 
 
(C) The dust found in the air bubbles trapped in Antarctica ice contained other minerals in addition to the ferrous material.
 This is additional information that was not a part of the premise. May be it contained sulfur, zinc, aluminum; who cares if it did. So far it carried ferrous materials, the scientists' hypothesis holds good. If the statement said, "the bubble contained other minerals that neutralized the inherent properties of ferrous materials", then it could be a weakening statement. If we assume that these gases may have caused the algae, then we are assuming too much.
 
(D) Sediment from the ocean floor near Antarctica reflects no increase, during the last ice age, in the rate at which the shells that diatoms leave when they die accumulated.
 
This statement may not be best in this world to weaken this hypothesis, but certainly is the best of the lot. It is attacking the hypothesis by finding out the fact that the algae's population didn't increase during the ice-age. Thus, the scientists hypothesis that increased population of algae caused the CO2 reduction is questionable.

Now, the scientists may come with a counter-argument that the tests used to actually analyze the sediment are rarely show correct results. Thus, despite your findings from the analysis of the sediments prove that the algae population didn't increase, it actually increased because your test findings are baseless.

Since we have to accept the statement as true, this directly casts a doubt on author's hypothesis.

It would be irrational to assume that the diatoms didn't die. If they didn't die, then they must still be present on the sea surface, making it easier for the scientists to hypothesize. 
 
 Correct.

(E) Algae that currently grow in the oceans near Antarctica do not appear to be harmed by even a large increase in exposure to ferrous material.
 Who said so that it would be harmed. Scientists said that the algae flourish in ferrous rich atmosphere. Strengthens part of the hypothesis.

smashzone · Answer

IMO, Answer is D.

If the scientists did not find an increase in the number of shells that diatoms leave when they die, then clearly there was no increase in the algae and thus the scientists' hypothesis that the ferrous material in the atmosphere was responsible for the increase in algae is wrong!

hsourabh · Answer

C can't be the answer as the passage doesn't mention the impact of other minerals anywhere.
'D' is the best choice since it mentions that there was no significant increase in algae population, hence no reason to believe that it could be the reason for low concentrations of CO2.

IMO D.

BMindful · Answer

Scientists analyzing air bubbles that had been trapped in Antarctic ice during the Earth’s last ice age found that the ice-age atmosphere had contained unusually large amounts of ferrous material and surprisingly small amounts of carbon dioxide. One scientist noted that algae absorb carbon dioxide from the atmosphere. The scientist hypothesized that the ferrous material, which was contained in atmospheric dust, had promoted a great increase in the population of Antarctica algae such as diatoms.

Which one of the following, if true, would most seriously undermine the scientist’s hypothesis?
 Brief: lots of ferrous material,BUT little CO2. Algae absorbs CO2. Conclusion: Scientist hypothesizes FM--> great increase in Algae.

(A) Diatoms are a microscopic form of algae that has remained largely unchanged since the last ice age  --> even though the diatoms are one type of artarctica algae, however, it is hard to strongly weaken the conclusion because it is just one kind of Algae. I consider this negligible weakening.

(B) Computer models suggest that a large increase in ferrous material today could greatly promote the growth of oceanic algae.  -->strengthen

(C) The dust found in the air bubbles trapped in Antarctica ice contained other minerals in addition to the ferrous material.  -->other minerals is out of scope.

(D) Sediment from the ocean floor near Antarctica reflects no increase, during the last ice age, in the rate at which the shells that diatoms leave when they die accumulated.  --> this suggests that there is no evidence that there are increase in shells which was died diatoms. So, no increase in diatoms. weaken. CORRECT

(E) Algae that currently grow in the oceans near ntarctica do not appear to be harmed by even a large increase in exposure to ferrous material.  -->lightly strengthen

gmatcrook · Answer

Although i understand D, I don't understand how to take out C.

The question says "if true" which means if you take the statements in the options to be true would it "most seriously" undermine the hypothesis.

How can C be out of scope or Irrelevant when the question itself brings it into scope when you view the argument and the option C as whole? The Scientist hypothesize that the ferrous material in the dust promoted the increase. If you get other minerals into the picture doesn't that question the hypothesis?

Please help clarify this. 
Thanks.

anshunadir · Answer

Scientists analyzing air bubbles that had been trapped in Antarctic ice during the Earth’s last ice age found that the ice-age atmosphere had contained unusually large amounts of ferrous material and surprisingly small amounts of carbon dioxide. One scientist noted that algae absorb carbon dioxide from the atmosphere. The scientist hypothesized that the ferrous material, which was contained in atmospheric dust, had promoted a great increase in the population of Antarctica algae such as diatoms.

Which one of the following, if true, would most seriously undermine the scientist’s hypothesis?

A) Diatoms are a microscopic form of algae that has remained largely unchanged since the last ice age.
 talks about diatoms(population has remained unchanged) in general, not specifically about Antarctica region. 
(B) Computer models suggest that a large increase in ferrous material today could greatly promote the growth of oceanic algae.
 Incorrect - Strengthens the argument 
(C) The dust found in the air bubbles trapped in Antarctica ice contained other minerals in addition to the ferrous material.
 The statement mentions that air bubbles contained other minerals but if other minerals caused increase in algae population is assuming too much for me. what if they were harmful... 
(D) Sediment from the ocean floor near Antarctica reflects no increase, during the last ice age, in the rate at which the shells that diatoms leave when they die accumulated.
 specifically talks about diatoms population around Antarctica region. Correct.  
(E) Algae that currently grow in the oceans near Antarctica do not appear to be harmed by even a large increase in exposure to ferrous material.
 neutral or a weak strengthner because it says ferrous material is not harmful to algae population.

mattce · Answer

Here's my take on these two:
C) There are a few materials; we hypothesize that ferrous material is the cause.
D) There has been a decrease in death, and thus there has unlikely been an increase in life.

"The scientist hypothesized that the ferrous material, which was contained in atmospheric dust, had promoted a great increase in the population of Antarctica algae such as diatoms"

For (C) to be correct, we are attacking the "ferrous material was the cause" issue.
For (D) to be correct, we are attacking the "increase in population" issue.

In my opinion, for those who say C is correct, you are in a way assuming that there was a - great increase - in the population, but that ferrous material was not the cause.

D is the correct answer because there could not have been a - great increase - in population with absolutely no change in mortality rate.

Pankaj0901 · Answer

While I understood the intended meaning of option D and why it is correct, I interpreted it slightly differently. Can an expert please point out why my interpretation is wrong?

My Interpretation:  
Count of shells didn't increase => count of Diatoms that died didn't increase (as they didn't leave shells) => More and more diatoms are present on the surface (as they seem to be living longer) => supporting the conclusion that diatoms increased during the ice age.

MartyTargetTestPrep · Answer

The main flaw in your reasoning is that you got the idea that "more and more diatoms are present on the surface" from nowhere.

Notice that you both decided that diatoms were living longer and that there were more of them without any evidence. All we know from (D) is that the rate of accumulation of diatom shells did not increase. There's no clear reason to believe that we can make the leap from that information to the ideas that there were more diatoms and that they lived longer.

Also, by the way, even if the diatoms did live longer, if there were more of them, then at a certain point, when many had lived for their longer lifespans, the rate of accumulation of shells would have increased. So, the idea that their living longer would have resulted in a long-term decrease in the rate of shell accumulation is also flawed.

Axwe7 · Answer

MartyMurray   KarishmaB

One question I have around option D), is that, I understand that the option says that an increase in the death rate was not observed. But, from that fact, how can we establish that it implies that the population did not grow substantially? After all, couldn't the longevity be extended, or is that too far of an assumption to make?

I chose option C) as to me, it was the strongest amongst the remaining 'poor' choices.

MartyMurray · Answer

Many things could have happened. For all we know, the longevity of diatoms increased or aliens came and took away most of the shells of the diatoms that had died. So, (D) does not confirm with certainty that the diatom population did not increase.

At the same time, (D) works well as the correct answer. Here's why.

The correct answer to a Weaken question doesn't have to definitively prove the conclusion untrue. It has only to provide a reason to doubt the conclusion.

(D) does just that, providing a reason to doubt that the population increased because evidence indicates that there was no increase in diatom shell deposits at that time.

Axwe7 · Answer

Thank you for your response Marty. For my comfort, would you think such a question would appear in the GMAT? I find D) to be a fairly weak answer choice. Let me know if I'm completely off

MartyMurray · Answer

A question that works like this one could absolutely appear on the GMAT. After all, information indicating that there was no increase in deposits of shells is a good reason to doubt that the population of diatoms increased.

So, unlike some LSAT questions, this one works like a GMAT CR question, meaning that your best move is to learn from it rather than hope one like it doesn't appear on your test.

guddo · Answer

The key point is that (D) is not merely about the  death rate . It is about the accumulation of diatom shells over the whole period.

If the diatom population had greatly increased, we would normally expect more diatoms to die over time and leave more shells in the sediment. Since no increase in shell accumulation is found, that is evidence against a major population increase.

Your longevity idea is possible, but it requires an extra assumption: that diatoms lived longer in a way that hid the expected shell increase. That is  too speculative .

(C) is weaker because the presence of other minerals does not show that ferrous material failed to promote algae growth.

Axwe7 · Answer

Thank you  MartyMurray  and  guddo

KarishmaB · Answer

Here is the conclusion: F errous material  promoted  a great increase in the population of Antarctica algae.

We need to weaken this. 
Age for which the algae lived is irrelevant here. Did their population increase substantially or not? If it did, then it will die off eventually, whether sooner or later. So no increase in shell remains makes us doubt whether the population actually increased.

There could be various reasons for the ice age to happen - that is not our concern. Focus on the conclusion - our concern is only whether the population of algae increased or not.

Scientists analyzing air bubbles that had been trapped in Antarctic

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Scientists analyzing air bubbles that had been trapped in Antarctic

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615 to 715 in 15 Days (Ria's Strategies)

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