Astronomer:
Observations of the Shoemaker–Levi comet on its collision course with Jupiter showed that the comet broke into fragments before entering Jupiter’s atmosphere in 1994, but they did not show how big those fragments were. In hopes of gaining some indication of the fragments’ size, astronomers studied spectrographic analyses of Jupiter’s outer atmosphere. After the fragments’ entry, these analyses revealed unprecedented traces of sulfur.
The fragments themselves almost certainly contained no sulfur, but many astronomers believe that the cloud layer below Jupiter’s outer atmosphere does contain sulfur. Since sulfur would have seeped into the outer atmosphere if comet fragments had penetrated this cloud layer, it is likely that some of the fragments were at least large enough to have passed through Jupiter’s outer atmosphere without being burned up.
In the astronomer’s argument, the two portions in boldface play which of the following roles?
The argument is trying to determine the size of the comet fragments. The first boldface introduces that issue: observations showed fragmentation but not fragment size. The second boldface supports the conclusion by ruling out the fragments themselves as the source of the sulfur.
So the sulfur likely came from the lower cloud layer, meaning some fragments were large enough to reach that layer without burning up.
A. The first is a claim that the astronomer seeks to show is true; the second acknowledges a consideration that weighs against the truth of that claim.
This is incorrect. The first boldface is not something the astronomer tries to prove; it sets up the issue. The second does not weigh against it.
B. The first is a claim that the astronomer seeks to show is false; the second acknowledges a consideration that weighs in favor of the truth of that claim.
This is incorrect. The astronomer does not try to disprove the first boldface.
C. The first reports observations that the astronomer argues have certain implications; the second is one of those implications.
This is incorrect. The second boldface is not an implication of the first. It is a separate premise used to support the final conclusion.
D. The first introduces the issue that the argument addresses; the second is a judgment advanced in support of the conclusion of the argument.
This is correct. The first introduces the uncertainty about fragment size. The second supports the conclusion by showing that the sulfur probably did not come from the fragments themselves, but from
inside Jupiter’s atmosphere.
E. The first provides evidence in support of the conclusion of the argument; the second acknowledges a consideration that weighs against that conclusion.
This is incorrect. The first mainly introduces the issue, and the second supports the conclusion rather than weakening it.
Answer: (D)