PrepTest 141, Section 4, 13. In early 2003, scientists detected…

How will the right answer fit in terms of support and conclusion?

Only the right answer will be support that must be true if the conclusion is true, but it will also be the only that supports the conclusion without bringing in anything new.

Highlight the main conclusion in the passage, if there is one:

any methane in the Martian atmosphere must have been released into the atmosphere relatively recently

[BACKGROUND]. [SUPPORT]. So [CONCLUSION].

Map the wording of the answers to the wording of the passage:

(A) Mars had no methane in its atmosphere prior to 2003

This answer happens at a different time than the conclusion, which is only about what’s happened “relatively recently”. That’s probably the best way to see this answer is bringing in something new. The methane around Mars now could be pretty recent even if there was no methane before 2003, so the conclusion isn’t relying on this info to be true.

(B) …is eventually exposed to sunlight.

This one connects the support about sunlight to the conclusion, without using wording stronger than the passage. It just says “eventually”, which definitely has to be true to make the conclusion work. If some methane never gets sunlight, there’s no reason to think it was released “relatively recently”. For all we know if could have been there basically forever, just hanging out.

(C) methane cannot be detected until…

Methane getting “detected” only came up in the background info. The author doesn’t connect detection to when methane “falls apart” or to “sunlight” or to getting released “relatively recently”. You’d have to come up with your own reasoning to explain how this supports the conclusion, and that’s never what an “assumption” does on the LSAT.

(D) the methane that the scientists detected…

…isn’t the methane mentioned in the conclusion. What the scientists detected is just background that clarifies the argument, but the author isn’t relying on anything being true about that methane to reach their conclusion about the “methane in the Martian atmosphere” now.

(E) methane in Earth’s atmosphere…

…is never mentioned or referenced in the argument. There’s no way anything must be true about Earth’s methane to make a conclusion about Martian methane work.

(B) is the correct answer.