Astronomer: Earth was bombarded repeatedly by comets and asteroids early in its history. This bombardment probably st...

Skylar on March 21, 2020

@shafieiava, happy to help!

(C) It is a claim for which some justification is provided and that is required in order to establish the argument's main conclusion.

There are two key factors about this answer that stand out to me as correct:
1. The phrase "some justification" provides notable leeway for us when evaluating the level of support present in the passage. The passage uses language like "probably" to get to the statement in question, which implies some level of support, but not necessarily full support.
2. The phrase "required in order to establish the argument's main conclusion" sets up a Necessary condition. To put this in context, it helps me to think of the Strengthen lesson. We know that, in a Strengthen with a Necessary premise question (which will usually contain the word "depends" or "requires" like this question does), the negation of the premise will bring about the falsity of the conclusion. In other words, we need to look for the premise that must be true when we are dealing with a Necessary premise question. The same is true here- if we negate the statement that "there could have been microbial life on Mars prior to there being such life on Earth" to "there could NOT have been microbial life on Mars prior to there being such life on Earth," then the passage's conclusion that "life on Earth may have started when living microbes were carried here from Mars on a meteorite" would completely fall apart. Therefore, we can say that the statement is required to establish the conclusion.

(D) It is a claim for which justification is provided and that, if true, establishes the truth of the argument's main conclusion.

To contrast (D) with (C) above, we should focus on the following two issues:
1. The phrase "for which justification is provided" overstates the level of solid support the passage provides for the statement in question. Since the passage does not offer strong enough support to clearly establish the statement, we should be wary of this unqualified claim.
2. The phrase "if true, establishes the truth of the argument's main conclusion" sets up a Sufficient condition. Again, we can think back to the Strengthen lesson. When we are dealing with a Sufficient premise, we are looking for a premise that will guarantee the conclusion. If it were true, would the statement "there could have been microbial life on Mars prior to there being such life on Earth" be strong enough to absolutely guarantee the truth of the conclusion that "life on Earth may have started when living microbes were carried here from Mars on a meteorite"? Not necessarily, so (D) is incorrect.

(E) 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 in order to establish that conclusion.

There are two parts to this answer choice:
1. The first part of this answer choice- that the statement provides "some support" for the conclusion- is accurate as we established with answer choice (C).
2. The second part of this answer choice- that the statement neither ensures the truth of conclusion nor is required to establish the conclusion- is what makes (E) incorrect. As we should notice, (E) is now stating the opposite of the claims made in (D) and (C). Since we established with (C) that the statement is required to establish the argument's main conclusion, (E) can be eliminated.

Does that make sense? Please let us know if you have any other questions!

shafieiava on March 24, 2020

Yes, this was very helpful! Thanks.