#4 - Scientists analyzing air bubbles that had been trapped

[kevin.hussain24]

hello,
Why is answer A wrong?

Thank you

[James Finch]

Hi Kevin,

It's ultimately irrelevant to the stimulus's argument whether diatoms are the same or different now vs the last ice age; all that matters is whether diatoms would have absorbed carbon dioxide from the atmosphere or not. As diatoms are algae and algae are plants, this is a safe assumption to make. This makes (A) ultimately irrelevant to the stimulus.

Contrast this with the correct answer choice, (D): if (D) is true, then there was likely no actual increase in the number of diatoms, which completely destroys the More Ferrous More Diatoms Less CO2 causal chain the stimulus is proposing, as there wouldn't actually be more diatoms, and the mystery of why there is so much ferrous material and so little CO2 in the bubbles would remain.

Hope this clears things up!

[kevin.hussain24]

Thank you James

[LSAT student]

This seemed like an unfair question because to pick (D) you'd need to understand something about diatoms and that they leave behind shells. This answer didn't make sense to me and so I just quickly eliminated it...
Please help!

[Adam Tyson]

That answer doesn't require you to know anything about diatoms and their shells, because the answer provides that information for you. The way the answer is worded - "the shells that diatoms leave when they die" - tells you that, in fact, dead diatoms (whatever they are) leave shells behind. We are told in the question stem to accept the answers as true, so all we need to do is accept that dead diatoms leave shells, and if there aren't more shells during that period then there probably aren't more dead diatoms, and thus probably not a lot more diatoms in general (because if you get a population boom of any living thing it would be reasonable to expect a corresponding increase in the number of those things dying over time).

A good prephrase would have been "something that indicates there may not have been an increase in stuff like diatoms." Answer D is the only one that comes close to that.

It's annoying, but it's fair!

[LSAT student]

Thank you for clarifying!

That answer doesn't require you to know anything about diatoms and their shells, because the answer provides that information for you. The way the answer is worded - "the shells that diatoms leave when they die" - tells you that, in fact, dead diatoms (whatever they are) leave shells behind. We are told in the question stem to accept the answers as true, so all we need to do is accept that dead diatoms leave shells, and if there aren't more shells during that period then there probably aren't more dead diatoms, and thus probably not a lot more diatoms in general (because if you get a population boom of any living thing it would be reasonable to expect a corresponding increase in the number of those things dying over time).

A good prephrase would have been "something that indicates there may not have been an increase in stuff like diatoms." Answer D is the only one that comes close to that.

It's annoying, but it's fair!

[Jonathan Evans]

A student asked me about this question via email, so I thought I'd share my reply here, in case this might help anyone else:

Let's illustrate the chain of causality here and what is known and unknown:

Event: high levels of ferrous material (known)
Event: increase in algae/diatoms (unknown, speculation)
Event: low levels of CO2 (known)

The conclusion's proposed causality is as follows:
High levels of ferrous material CAUSED increase in algae/diatoms CAUSED low levels of CO2

The core issue is that we don't even know that there was more algae/diatoms. This is just a speculative cause.

If we attack the idea that excess algae/diatoms were there at all, then we have fundamentally disrupted this causal chain.

In contrast, we know that there was more ferrous material. If we additionally know that there were other minerals, this doesn't disrupt causality because we still don't even know whether there were any algae there. We could speculate that algae, if it were there, might have been caused by some other mineral, but the simple presence of other minerals does not really disrupt the possible ferrous-algae causal connection.

Here's an analogy:

Farmer MacGregor has noticed a big increase in rabbits in his farm. He speculates that the MiracleGrow fertilizer he used has caused a big increase in carrots which has led to the additional rabbits.

Answer choice (C) would say something like this: In addition to MiracleGrow, the soil in the farm also contained earthworms.

Answer choice (D) would say: There is no evidence there are any additional carrots in Farmer MacGregor's farm.

Even if the soil contained earthworms, we still really haven't hurt the idea that MiracleGrow caused carrots which caused rabbits.

Answer choice (D) tells us, hey, there weren't even carrots at all.

This is a much more direct attack on the conclusion.