Q4 - Scientists analyzing air bubbles

[htesra]

Please show me how D is the correct answer. I think the whole scientific topic intimidates me.

[giladedelman]

Thanks for your question.

So, the scientists are checking out these air bubbles trapped in ice from the ice age, and they find a lot of ferrous material and surprisingly little carbon dioxide. One of the scientists hypothesizes (that is, argues) that the reason for this result is that the ferrous material led to an increase in algae populations, which in turn sucked a lot of carbon dioxide from the air.

We're looking for an answer choice that weakens this hypothesis.

(D) fits the bill because if there was no increase in diatom shells, then it's pretty unlikely that this type of algae increased in population; if there were more of them, why don't we find more shells?

(A) is irrelevant. Who cares if they've remained unchanged?

(B) actually strengthens the argument somewhat by supporting the connection between ferrous material and algae population growth.

(C) is irrelevant; it doesn't matter whether there were other minerals in the bubbles.

(E) strengthens the argument ever so slightly by suggesting that ferrous material doesn't harm algae populations.

Does that clear this one up for you?

[ebrickm2]

Isn't it also an assumption that the ferrous materials was the sufficient cause for the assumed growth of algae.

And that C would weaken this assumption by suggesting that there is an alternative cause?

[ManhattanPrepLSAT1]

Thanks for posting your question! The answer to your question is no, and no

It's not an assumption of the argument that the ferrous materials caused an increase in the Antarctic algae - it's the conclusion of the argument!

Answer choice (C) does not provide an alternative cause since there is no reasonable expectation that the "other minerals" could have caused an increase in Antarctic algae.

There's another issue with answer choice (C). We're not just looking to undermine a causal relationship. We're asked to undermine an explanation - which includes the possibility of whether or not there was an increase in Antarctic algae in the first place. This one's not as straightforward as a simple mistake between correlation and causation, since part of the causal explanation in the conclusion isn't even established to have occurred - the rise in algae.

Your tactic would be more appropriate when we have the standard two events co-occurring and then a conclusion that posits that one of the two events caused the other to occur. Even then, answer choice (C) would still need to have a reasonable chance of representing an alternative cause. Nothing about "other minerals" gives us this reasonable expectation.

Hope that helps, and let me know if you still have further questions on this one!

[leinsdorf]

I found answer D troubling because it referred to the death of the diatoms rather than the proliferating of them. Should I have reasonably drawn a connection between the ice-age and the death of the diatoms? Had answer D referred to finding diatom shells AT THE END OF or AFTER "the last ice age" I might have drawn the connection, but as-is it was not so clear.

Is there another explanation?

[nandy_millette]

Hi leinsdorf,

Before I looked at the answer choices I thought that the correct answer would suggest that something else absorbed the carbon dioxide, maybe some other type of algae not necessarily diatoms or maybe some other material all together?

So that's why C was so tempting to me but then I thought-

C- Contained other material in addition to ferrous material- so maybe something else caused the reduction in carbon dioxide? okay but what exactly?? too vague-wrong answer

D- was the correct answer to me because it directly attacked the scientist hypothesis by suggesting that there may not of been a large increase in diatoms as hypothesized by the scientist.

The answer choice is saying that when diatoms die in accumulated numbers they leave behind shells, evidence (sediments from near the ocean floor) shows there was no increase in the number of shells left behind (during the last ice age) which is expected when diatoms die is accumulated numbers so there was essentially no increase in the number of diatoms

So although D is not telling me exactly what caused the small amount of carbon dioxide it is telling me that surely it was not the increase in diatoms as the scientist hypothesized.

To more directly address your concern about the answer choice referring to "during the last ice age" and not the end or after refer back to the stimulus it specifically states:

"Scientist analyzed air bubbles that had been trapped in Antarctic ice during the Earth's last Ice Age found....

So, the stimulus and the correct answer choice are both referring to during the ice age not the end of or after

[Mab6q]

Can someone please expand on the reasoning in this argument. I know that the conclusion is the explicitly stated hypothesis, but is the support the fact that algae absorb carbon dioxide. If the author taking for granted that just because something could've been the cause it was indeed the cause. Thanks for the help.

[sumukh09]

Can someone please expand on the reasoning in this argument. I know that the conclusion is the explicitly stated hypothesis, but is the support the fact that algae absorb carbon dioxide. If the author taking for granted that just because something could've been the cause it was indeed the cause. Thanks for the help.

The author is hypothesizing so he's not taking anything for granted when making his argument. The reasoning he utilizes to arrive at his hypothesis is this:

unusually large ferrous materials ----> possible that the unusually large ferrous materials caused increase in Antarctic algae such as diatoms

The part about algae absorbing carbon dioxide from the atmosphere is also used to support the conclusion that it's because of the unusually large ferrous material that there's an increase in algae. Remember that there's also a surprisingly low amount of carbon dioxide; so the basically what's being hypothesized here is this

unusually large ferrous material ---> increase in algae ---> algae absorbs CO2, so that's why surprisingly low amounts of CO2

[tara_amber1]

I just wanted to add to this by saying answer choice (A) may have tripped up a few others as did myself.

(A) is very similar to (D), but you have to pay close attention to the wording. I think this was preying on students who were moving through the questions too quickly.

(A) says that Diatoms are a form of algae that has remained largely unchanged. BUT WAIT, this is just talking about the subject - Diatoms - that has itself remained unchanged. Meaning it hasn't changed color, it hasn't deformed into another shape, something like that.

(D), the correct answer, refers to the amount of algae that has remained constant. We know this from "reflects no increase," the game-changer in separating (A) and (D). The stimulus says the amount of algae has increased. So (D) weakens.

[WaltGrace1983]

Can someone please expand on the reasoning in this argument. I know that the conclusion is the explicitly stated hypothesis, but is the support the fact that algae absorb carbon dioxide. If the author taking for granted that just because something could've been the cause it was indeed the cause. Thanks for the help.

The author is hypothesizing so he's not taking anything for granted when making his argument. The reasoning he utilizes to arrive at his hypothesis is this:

unusually large ferrous materials ----> possible that the unusually large ferrous materials caused increase in Antarctic algae such as diatoms

The part about algae absorbing carbon dioxide from the atmosphere is also used to support the conclusion that it's because of the unusually large ferrous material that there's an increase in algae. Remember that there's also a surprisingly low amount of carbon dioxide; so the basically what's being hypothesized here is this

unusually large ferrous material ---> increase in algae ---> algae absorbs CO2, so that's why surprisingly low amounts of CO2

I don't know if I am misreading your rationale but I am seeing the argument a bit differently:

Ice-age atmosphere contained unusually large amounts of FM, small amounts of CO2
+
Algae absorb CO2
-->
FM promoted an increase in algae, such as diatoms

The parts that we can nitpick include the following:

(1) Why did the FM have to promote anything?
(2) Why would it have to be algae that causes the C02 shortage?
(3) Why specifically diatoms?

I feel like the correct answer to any of these could have looked like

(1) "Ferrous material have always been dormant and useless, unable to spawn any organism but itself."
(2) "It has been noted that X was present in large amounts during the last Antarctic ice age, and X stays alive by absorbing CO2."
(3) Answer choice D.

Thus, I think (1), (2), and (3) are ALL taken for granted and we should treat the argument as doing such.

[LsatCrusher822]

D seems a bit far of a reach because we have to assume that the diatoms died at the end of the last ice age. There is no indication of that fact in the stimulus. Typically wrong answer choices for weaken/strengthen questions have unwarranted conditional statements. I thought we can only mark these as correct if the situation fits the stimulus. Could somebody please clarify?

Also is E incorrect due to the word "harmed"? Would this be correct if it said "affected"? Thank you

[anurag111284]

D seems a bit far of a reach because we have to assume that the diatoms died at the end of the last ice age. There is no indication of that fact in the stimulus. Typically wrong answer choices for weaken/strengthen questions have unwarranted conditional statements. I thought we can only mark these as correct if the situation fits the stimulus. Could somebody please clarify?

Also is E incorrect due to the word "harmed"? Would this be correct if it said "affected"? Thank you

As for D: Diatoms dying during Ice Age is surely an assumption, but it is plausible by 'commonsense standards' and is neither 'superflous or incompatible with the passage'/stimulus. The Ice Age, like any Age, must have lasted a long time and it is hard to believe algae would have outlived the Ice Age. The LSAT permits us to make such assumptions as indicated in the Directions on top of each LR section states.

As for E: E has several problems. First, it talks about the present age while we are concerned with Ice Age. Second, even if one assumes it is relevant (a BIG assumption), like you said, it is incorrect because it does not help us show that ferrous material did not promote algae growth.

If E said "affected": This would certainly help E. But there are other issues with E, mentioned above. Taking care of them, if E said, "Algae that grow in the oceans near Antarctica are not affected by even a large increase in exposure to ferrous material", it surely weakens the reasoning in respect of the assumption/gap identified by WaltGrace above i.e. "Why did the FM have to promote anything?"

Hope this helps.