Critical Reasoning

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.


Currently there is a lot of tussle between option C and option D at the forum.Will request an instructor to clarify the same.

Hi,
Hope you dont mind me commenting on the thread as I am no expert. But I see a very obvious flaw in option C.

C requires the additional assumption that the other minerals present in the bubble do affect algae growth. No where in the stimulus or the answer option this fact is mentioned. So C cannot be the correct answer.

As you cannot rope in any additional info besides whats given in the answer choices, answer choice D is correct.

Hi I have also marked D with the same logic. But there is a lot of heated debate between option C and option D with 50 percent supporting C and 50 percent supporting option D. Thus was really confused. Lets wait for others to reply on the thread..

C is out of scope. Hence D

IMO D.
C talks about other materials. But they may or may not be relevant. If the choice would have stated that the other materials are also instrumental in algae growth - ans would have been C

To me only D makes sense.

If you need an expert reply I will see what I can do!

This one is an LSAT question. It is listed in an LSAT forum as being from test 19, the second section, question 4.

Answer Choice D is the correct answer. As mentioned above by bblast choice C requires too much of an assumption of information that this not in the stimulus and not in the answer choice.

When I read choice C "The dust found in the air bubbles trapped in Antarctica ice contained other minerals in addition to the ferrous material." I said, well that is to be expected, right? Shouldn't there be other things in the air? This in no way impacts the diatoms in the Antarctic.

As bblast said for this to be correct we would need to know that the other minerals did not increase or actually harmed the growth of the diatoms.

I mean D indicates that there actually WAS NO INCREASE in the diatoms.

Since this in an LSAT question I will give you the LSAT lingo for this one -- this shows the cause (ferrous materials) without the effect (there was not increase in diatom shells). This is a classic way to weaken a cause and effect.

It is like saying that peanut butter makes me ill and then I eat peanut butter and do not get ill. So the cause is there but not the effect.

David@VeritasPrep wrote:If you need an expert reply I will see what I can do!

This one is an LSAT question. It is listed in an LSAT forum as being from test 19, the second section, question 4.

Answer Choice D is the correct answer. As mentioned above by bblast choice C requires too much of an assumption of information that this not in the stimulus and not in the answer choice.

When I read choice C "The dust found in the air bubbles trapped in Antarctica ice contained other minerals in addition to the ferrous material." I said, well that is to be expected, right? Shouldn't there be other things in the air? This in no way impacts the diatoms in the Antarctic.

As bblast said for this to be correct we would need to know that the other minerals did not increase or actually harmed the growth of the diatoms.

I mean D indicates that there actually WAS NO INCREASE in the diatoms.

Since this in an LSAT question I will give you the LSAT lingo for this one -- this shows the cause (ferrous materials) without the effect (there was not increase in diatom shells). This is a classic way to weaken a cause and effect.

It is like saying that peanut butter makes me ill and then I eat peanut butter and do not get ill. So the cause is there but not the effect.

Hi David

Well, i may not be correct, but what i, on the very first look at this problem, tried to pre-phase was to find some option that could establish that it was not ferrous material but some other alternate cause that actually could have resulted in the abundant algae population. While doing this i presume that the part of the scientist's hypothesis that talks about the increase in algae population is correct. Only the cause for this result is at question.

But, doesn't option D tells us that, forget the cause, even the algae population remained unchanged during that particular ice-age, thus defying the premise itself.

Had it been said for some other preceding ice-age, or say, for some other hypothetical planet, then the logic of Cause but No Effect were more applicable.

I may be wrong also, but request you to pl clarify this doubt.

Thanks & Regards

Looking at this one more closely - you will see that the effect that they are actually trying to explain is the decreased carbon dioxide levels. Remember the effect is a fact that must be true and as you indicated cannot be contradicted. Not even by the answer choices. So it is important to realize that the effect is not the diatoms but is the increased carbon dioxide.

note that the text is trying to explain the "surprisingly small amounts of carbon dioxide." So what is supposed to have caused the decreased carbon dioxide? Because algae absorb carbon dioxide "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."

So they are saying that the observed low level of carbon dioxide was caused by a "great increase in the population of Antarctic algae such as diatoms." The evidence for the diatoms is the ferrous material.

Remember that this is an LSAT question and the LSAT is not limited to only offering an alternate cause in order to weakening. The GMAT would primarily be looking for an alternate cause.

In this case choice D indicates that basically there was no increase in diatoms. The low level of carbon dioxide cannot be denied it is a fact to be explained. But the purported cause - Antarctic algae does not seem to have been there.

Does that help?

Thanks David for the explanation.

I find this question to be of a certain different kinds, where the explicitly written conclusion, "scientist hypothesized that the ferrous material, which was contained in atmospheric dust, had promoted a great increase in the population of Antarctica algae" is also not the main conclusion. The main conclusion being the fact that this abundant algae population caused the CO2 to diminish.

In this scenario, definitely any option that tells me that the talked-about cause was actually not present, but the effect, the decreased CO2 in atmosphere, was always there, will attack the conclusion.

A different sort of difficult problem though.

Thanks a ton David, for your time and patience.

Regards

Most, if not all, of the other answers are off topic (or out of scope). I would choose D.

Thanks David for the explanation !!!