PrepTest 114, Section 2, Question 17
Selena: Asteroid impact on the Earth caused the(115 more words not shown)
Trent's argument assumes(1 more words not shown)
- Aany collision of(16 more words not shown)
- Bdinosaurs in the(19 more words not shown)
- Cany event that(14 more words not shown)
- Ddust from the(17 more words not shown)
- Eno more than(15 more words not shown)
Reading the argument
What if there was more than one asteroid?
Selena's story is understandable: an impact raises dust, the dust blocks sunlight, cooling harms dinosaurs or the vegetation they depend on. The dust layer and crater could support that account. I'd still ask whether a dust layer could have another source, such as a volcanic eruption, but that is only an alternative to investigate.
Trent's first objection is that this crater is too small to account for the needed dust. That might show this one impact wasn't enough. It doesn't yet rule out several impacts contributing to the effect together.
His second objection raises another question. Why would an asteroid's effects have to finish within a year or two? An impact could happen quickly while its consequences for vegetation and animals continued for much longer. We haven't been given a rule that a sudden cause must produce a sudden extinction.
What we’re looking for
For the assumption, I'd focus on the possibility of other impacts. Trent uses the limits of this one crater to reject asteroid impact as the explanation. That reasoning needs to exclude the possibility that additional large asteroids contributed during the extinction period.
Working the answers
- A
The argument doesn't require every impact to have occurred on land. Whether an asteroid struck land or water is separate from whether more than one large impact contributed. Trent's objection to the size of this crater doesn't establish a general restriction on possible impact locations.
- B
The debate concerns effects extending beyond the immediate impact, including dust and cooling. Trent doesn't have to specify that every dinosaur outside the direct-impact zone would survive. He could allow some nearby deaths while still rejecting the impact as an explanation of the wider extinction.
- C
Trent discusses this extinction, not every event that unfolds over a long time. Even if he thinks an asteroid cannot explain this event, he needn't believe every lengthy event has many different kinds of causes. C adds a sweeping rule beyond his reasoning.
- D
Too little cooling to cause the extinction is different from no cooling at all. Trent could concede that an impact had a small climatic effect while maintaining that it couldn't explain the disappearance of the dinosaurs. D denies any effect, which is more than his argument needs.
- ECorrect
This excludes the multiple-impact possibility behind the first objection. If several large asteroids struck during the relevant period, the dust from this one crater wouldn't have to do all the explanatory work. The combined effects might be enough even if this impact alone was too small.
“No more than one” is the restriction Trent relies on when he moves from this crater's inadequacy to ruling out asteroid impact. It doesn't prove that his other objection about timing is sound, and we needn't treat it as a complete defense of the argument. It supplies a required part of the reasoning he uses.
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