Q20 - Astronomer: Earth was bombarded

[ManhattanPrepLSAT1]

I don't know why I love questions about asteroids and the solar system so much, but I do!

The astronomer asserts that life on Earth may have gotten its start from a meteorite arriving from Mars. The argument offers two main reasons. First, there are meteorites that have landed on Earth that are from Mars. Second, since Mars escaped severe bombardment, microbial life could have existed much earlier on Mars than on Earth.

The question asks about the role of the statement that microbial life could have existed much earlier on Mars than on Earth. The easy answer is that it's an intermediate conclusion. But this is not an easy question. The correct answer choice is (C). The claim has some support and is required for the main conclusion to be possible--that life on Earth may have gotten its start from a meteorite arriving from Mars. Without first existing on Mars, Earth could not have acquired life from Mars.

Incorrect Answers
(A) is contradicted. Evidence is provided for this claim.
(B) is contradicted. Evidence is provided for this claim.
(D) is too strong. The claim would not prove the argument's main conclusion.
(E) is contradicted. The claim is required in order to establish the argument's main conclusion.

#officialexplanation

[jennifertrimo]

I don't understand why the answer is (C) as opposed to (D)?

[yzbyyanxin]

I also picked D in PT. When did the blind review, i still didn't see why D is wrong. Is that because "establish" means "leads to", but the claim that microbial life having been on Mars is not sufficient to come to the conclusion?

[JorieB701]

Okay, so when I was doing this in a timed PT I recognized that it was a subsidiary conclusion, that it had some support.. but I got tricked by all the "probably," "could have been," "may have started" language. That is why I was afraid to choose C and ended up going with E.

But now I go back and see, obviously life had to have originated on Mars before it originated on Earth, otherwise the conclusion wouldn't make sense. lol.

Is that how these are meant to be answered? If an answer choice for a role question says, "required in order to establish the argument's main conclusion," as it does in C, can we just negate it like a necessary assumption question?

And for D, what would that look like if it were, in fact, the right answer? Would the argument have offered the sentence in question as something sufficient to make the conclusion true?

[ohthatpatrick]

You got it.

This is the only Role question I've ever seen (as far as I can remember) that also tested whether an idea was Necessary or Sufficient, so don't expect to need to do this analysis on most Role questions.

But anywhere we see it on the test, we evaluate it the same way.

IS IT NECESSARY? = if negated, would it badly weaken the argument?
IS IT SUFFICIENT? = if this is true, can the conclusion be 100% derived?

[JeffW669]

The issue between C and D is indeed necessary vs. sufficient. Because of the many qualifiers in the argument, that can be hard to follow, as it was for me during the timed test. What I sometimes find helpful in these situations is thinking of hypotheticals to eliminate answers.

C: It is certainly a claim that is partially justified (one factor, of potentially many, points to the possibility of microbial life on Mars); and this claim is also certainly required to establish the main conclusion (if microbial life did not exist on Mars, then meteorites couldn’t have carried microbial life from Mars to Earth).
vs.
D: It is a claim that is justified, but not completely (maybe Mars was too cold to support microbial life, so there couldn’t have been such life on Mars even without asteroid/comet bombardment); and it establishes the possibility but not the certainty of the argument’s main conclusion (maybe microbial life can’t survive the trip from Mars to Earth, so the conclusion is not valid).