PrepTest 114

Incorrect. There's no discussion of differing impacts of asteroid impacts on land vs. sea. We can't even assume that a sea impact wouldn't result in dust clouds being kicked up—maybe the asteroid itself creates the dust while going through the atmosphere or the wind it generates kicks up dust.

Incorrect. Trent believes the extinctions couldn't have been caused by an asteroid impact, but that doesn't mean he can't believe that the asteroids killed many, many dinosaurs in the vicinity of that impact site. As long as it didn't kill off the entire species, the argument can still hold.

Incorrect. Trent establishes that the dinosaur extinctions took place over "many years" (which isn't necessarily a "long period" but let's assume it is for a second). However, he concludes that it must have been due to "some other kind of cause." He's not saying that it has "many" different kinds of causes just one other one. If he had concluded that the extinction was caused by many factors this answer would be closer to being correct.

Incorrect. Trent believes that there is a certain amount of dust that would be sufficient to cause cooling, as witnessed by his statement that the crater isn't "large enough" to produce the "requisite amount" of dust. This answer is therefore not required for his argument to work.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Necessary Premise

Stimulus Summary:
S: There's dust and impact evidence that a massive asteroid struck the Earth around when the dinosaurs died, so that's the cause of their extinction.

T: The impact wasn't big enough and the extinction took place over many years, so the dinosaur extinction must have been caused by something else.

Answer Anticipation:
The argument is asking for an assumption of Trent's argument. When the question stem is phrased this way, the correct answer is always a necessary assumption (and it's usually a sufficient assumption, as well).

Here, we need to focus on Trent's argument. He states that the asteroid impact crater brought up by Selena isn't big enough to have killed off the dinosaurs, and they went extinct over several years, not all at once as would presumably have been the case if the asteroid impact killed them. From this, he rules out asteroid impact as the cause of the extinction.

However, all of his evidence shows that the one asteroid cited by Selena can be ruled out as the sole cause of the extinction. His conclusion, however, is about any potential asteroid impact. As such, the argument assumes that the asteroid that struck in the Yucatan is the only one that could have contributed to the dinosaur extinction. Let's find an answer reflecting that.

Answer Explanation:
Trent does bring up some valid points to show that the asteroid cited by Selena as the cause of dinosaur extinction isn't the full cause. However, that allows the conclusion that this one asteroid didn't cause the extinction, not that no asteroid, or no combination of asteroids, didn't result in that extinction. If more than one large asteroid struck the Earth during this time period, then together and over a period of years they may have kicked up enough dust to cool the Earth and lead to the dinosaur extinction. This answer is therefore necessary for Trent's argument to hold by ruling out a possibility that Trent doesn't address but would destroy his argument.

Key Takeaway:
Whenever an argument discusses a specific case in the premises but then draws a more general conclusion, it's assuming that the specific case it cites is representative or makes up the whole story. Always consider whether the specific case could be part of a larger "story" in such an argument.