Q13 - In early 2003, scientists

[ManhattanPrepLSAT1]

This argument appeals to a rule in support of it's conclusion. It says that when exposed to sunlight, methane breaks down and falls apart. And since the scientists detected methane in the atmosphere of Mars, the scientists say that it must have been recently released.

Do we really know that the methane was exposed to sunlight? Not based on the information in the stimulus. And the rule doesn't apply to methane that has NOT been exposed to sunlight. So this argument assumes answer choice (B).

Incorrect Answers
(A) is too strong. Even if there were some methane in the environment prior to 2003, the argument remains unchanged.
(C) is too specific. How methane was detected is more information than we need, which was simply that methane was detected.
(D) undermines the argument by suggesting that the methane need not be recently released, since what was being detected was methane that had possibly fallen apart a long time ago.
(E) is too weak. This is consistent with the claim that methane in the Martian atmosphere would fall apart when exposed to sunlight.

#officialexplanation

[priyanka.krishnamurthy]

Hi:
I am pretty confused on the justification for B on this one. I think the "all" is throwing me off. I originally chose D, trying to link the ultraviolet radiation to the specific methane in the atmosphere that was detected. Could someone please help? What is the significance of "relatively recently" in the last part of the statement? Thanks in advance!

[aaronwfrank]

The most important factor in B being correct is that the stim assumes that since methane falls apart when exposed to sunlight, this methane must have been released recently.

If B is negated to "some methane in the atmosphere of Mars is not exposed to sunlight," then the contention that this methane must have been released recently is not necessarily true. If not all of the methane in the atmosphere is exposed and broken apart, this leaves open the possibility that the methane might not be recent.

[abrenza123]

I've spent a lot of time trying to wrap my head around this question, but I am honestly really confused about the core/missing assumption in this argument. I keep thinking I almost grasp the explanation, but am not quite there and keep overthinking it to the point that most of the other answers look tempting as well. How does methane falling apart relate to methane being released into the atmosphere relatively recently??

W/ answer B, to assume all methane in Mars atmosphere is eventually exposed to sunlight means that all methane in the atmosphere eventually falls apart. To me, eventually extends beyond relatively recently, so couldn't the methane detected have been released into the atmosphere a long time ago??

I feel like to get to answer choice B you have to make a ton of assumptions, such any methane in the atmosphere released PRIOR to "relatively recently" would have been exposed to sunlight before the detection. If that wasn't true, wouldn't that destroy the argument?? leaving open the possibility that the detected methane was old? How could that NOT be true and the argument still hold??

ALSO, even if some methane isn't exposed to sunlight, how does that destroy the argument?? That leaves open the possibility that there was methane released longer than relatively recently, but also couldn't methane not ever be exposed to sunlight and this was the FIRST TIME methane was let into the environment??

How is the assumption that all methane in Mars eventually being exposed to sunlight necessary to the argument?

[ohthatpatrick]

The correct answers to Necessary Assumption come in two main forms:

1. Supplying a Missing Link or Missing Trigger-Fact
(we call the former thing "Bridge ideas", as they play connect-the-dots with ideas from the argument. The latter thing is less common, but if we're provided with a conditional but never told the trigger was factually triggered, then sometimes we're just missing that fact)

In either case, the correct answer contains familiar wording, because it's either linking together two ideas from the argument or it's supplying a factual statement that matches the trigger of a conditional in the argument.

2. Ruling out a potential objection
(we call these Defender ideas)


When I read a NA stimulus, I basically start off thinking I'll probably be looking for #1 type stuff (it's more than 50% of answers but probably only about 65-70% of the time)

If I don't see a missing link or a missing fact, then my brain immediately goes into typical Debate mode (like we would for Flaw, Strengthen, Weaken, Evaluate)

I think:
GIVEN THIS evidence,
HOW CAN I ARGUE the anti-conclusion?

Here I would be thinking,
GIVEN THAT
they detected methane in Mars's atmosphere in 2003
and
methane falls apart when hit by UV radiation

HOW CAN I ARGUE THAT
at least some methane in the Martian atmosphere was NOT released into the atmosphere recently?


I start thinking, "Why can't I just say that some of the methane in the Martian atmosphere is from 1,000 years ago?"

The author would say, "Because, dude, how's methane gonna last 1000 years in the Martian atmosphere? It falls apart the second it's hit by UV radiation?"

To which we could respond, "Who said that all the methane gets hit by UV radiation? What if there is some methane released 1,000 years ago on the 'dark side' of Mars and it never got hit by UV radiation? Wouldn't that mean that at least some methane in the Martian atmosphere was NOT released recently?"

In order to rule out my objection, the author has to assume that
"Any methane that was released 1,000 years ago would have already been hit by methane and broken apart"

If you negate (B), it's saying that
"at least some methane in the Martian atmosphere is never exposed to sunlight (thus never exposed to the UV radiation in sunlight, thus once that methane is released, it could potentially continue to hang out in the Martian atmosphere forever)

That's a huge weakener for the argument. No, it doesn't PROVE that some methane in Mars's atmosphere is still there from being released a long time ago (because we don't know whether any methane was released a long time ago). But negations don't have to DISPROVE the conclusion. They just have to weaken the argument.

Teachers and books tend to oversell the negation test as: "the correct answer, when negated, will TOTALLY DESTROY the argument". That's not true. Sometimes, sure.

But just think of Necessary Assumption as:
"Which answer, if negated, would most weaken the argument"
and you'll never be led astray.

However, when the correct answer is more of a #1 style of Bridge Idea, you might find it easier to think of the correct answer as
"Which answer is clearly something the author was thinking, without going overboard"