Premise: 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.

Conclusion: ferrous material 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.
Only Diatoms has remained unchanged; other types of Algae may have increased - we do not know

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

(C) The dust found in the air bubbles trapped in Antarctica ice contained other minerals in addition to the ferrous material.
Something else besides Ferrous material might be the reason

(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.
No increase in death; does that mean the population decreased? NO

(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. No harm because of ferrous material but does it benefits the growth?

Only C is coming close to undermining the argument.
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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.
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Answer D according to me.

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.

Summary: Scientists found that the atmosphere during the last ice age had large amounts of ferrous material and very less carbon dioxide. Explanation for very less carbon dioxide was that algae absorbed it.
Hypothesis: The increase in algae was because of the ferrous material.

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

Thought process: How can we weaken the Hypothesis?
Either we say the cause of the increase was not ferrous material, or we say there was no increase in algae whatsoever!
"No-increase-whatsoever" gives a lethal blow to the hypothesis!

A) Diatoms are a microscopic form of algae that has remained largely unchanged since the last ice age.
Talks about Diatoms, but not about "no increase whatsoever"

(B) Computer models suggest that a large increase in ferrous material today could greatly promote the growth of oceanic algae.
Says there was "definitely an increase!", thereby strengthening the argument.

(C) The dust found in the air bubbles trapped in Antarctica ice contained other minerals in addition to the ferrous material.
Talks about "other minerals". This does not imply "other minerals caused the increase in algae." Close, but definitely not convincing enough to destroy the hypothesis

(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.
No increase in the mortal remains of algae! No increase in algae whatsoever! This is surely the answer

(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.
Talks about algae of today and not about algae during the last Ice Age.

So answer according to me is D.
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November 5, 2011: GMAT 1 630 Q42 V35

Answer should be A, because here if we look at choice D, which says "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 choice shows no meaning to me, as weakening is concerned. as there is no increase in sediments, which points to shell that diatoms leave when they die.

As for A choice is concerned" Diatoms are a microscopic form of algae that has remained largely unchanged since the last ice age." Diatoms are unchanged, that is giving some counter to conclusion "great increase in the population of Antarctica algae such as diatoms.".