Astronomer: Earth was bombarded

A free, expert breakdown of this official LSAT Logical Reasoning question.

TopicsRole

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Stimulus

Astronomer: Earth was bombarded repeatedly by comets and asteroids early in its history. This bombardment probably sterilized the surface and prevented life from originating during this early period in Earth's geological history. Meanwhile, Mars escaped severe bombardment, and so there could have been microbial life on Mars prior to there being such have started when living microbes were carried here from Mars on a meteorite.

What this question is testing

Role

Your task

Break the argument into its conclusion and evidence, then do exactly what the question stem asks with that structure.

Common trap

Answers that sound relevant to the topic but don't connect to the argument's actual reasoning.

Winning move

Predict what a right answer must do, then test each choice against the conclusion-evidence gap.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question

20.

Which one of the following most accurately describes the role played in the astronomer's argument by the statement that there could have been microbial life on Mars prior

Answer choices

Opposite: Justification is Provided6% picked this
It is a claim for which no justification is provided but that is required in order to establish
This is a mean answer. This claim is necessary for the conclusion that "life on Earth could have come from Mars". But there was justification provided. In fact, we can even see that this claim was prefaced by the word "so", indicating that the claim is a conclusion. Why should we believe that there could have been microbial life on Mars? Because Mars was not getting pummeled by comets and asteroids.
6%
Opposite: Justification is Provided Not Sufficient3% picked this
It is a claim for which no justification is provided and that, if true, ensures the truth of
This claim is not sufficient. The fact that there could have been microbial life on Mars does not prove that "life on Earth could have come from Mars". And there was justification provided. In fact, we can even see that this claim was prefaced by the word "so", indicating that the claim is a conclusion. Why should we believe that there could have been microbial life on Mars? Because Mars was not getting pummeled by comets and asteroids.
3%
Correct60% picked this
It is a claim for which some justification is provided and that is required in order to establish
Why this is right
Is there justification provided for the idea that microbial life could have started on Mars? Yes, that's why it's wearing the word "so", which is a conclusion indicator. The support was the previous fact, that Mars was not getting ravaged by incoming objects. Is this claim required for the conclusion? Yes, try negating it: if "microbial life couldn't have started on Mars" would that hurt the author's story? Of course! The meteorite delivery service from Mars to Earth would be carrying no packages of life.
Skill tested: Role · how this choice captures the argument's function is the move to repeat next time.
60%
Not Sufficient17% picked this
It is a claim for which justification is provided and that, if true, establishes the truth of
The first half is true, as we've discussed in (A), (B), (C). The second half is not, as we've discussed in (B). Knowing that "microbial life could have started on Mars", does not establish the certain truth of "life on Earth could have started with microbes delivered via meteorite from Mars".
17%
Is Necessary14% picked this
It is a claim that provides some support for the argument's conclusion but that neither ensures the truth of that conclusion nor is required
It does provide support for the conclusion. It isn't sufficient. But it is necessary, as discussed in (A) and (C).
14%

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