PrepTest 143, Section 4, Question 8
The giant Chicxulub crater in Mexico provides indisputable(86 more words not shown)
Which one of the following,(7 more words not shown)
- AThe vast majority(22 more words not shown)
- BThe size of(23 more words not shown)
- CFossils have been(21 more words not shown)
- DThere is no(22 more words not shown)
- EDuring the period(26 more words not shown)
Reading the argument
Could an impact that large have effects far beyond the crater?
I'd want to investigate that before ruling it out as the cause of most of these extinctions. For example, what if the impact threw dust into the air that spread widely and blocked sunlight? That's a possible mechanism to investigate, not a fact established by this passage.
The older, larger craters also make me ask whether those earlier situations were comparable. What organisms were around then? Perhaps there weren't similar populations vulnerable to the same effects. A large crater without known extinctions doesn't automatically tell us what happened when this particular asteroid struck.
What we’re looking for
The question asks us to weaken the argument. My initial thought is to show that the impact could have had broader effects than the author allows. Keep the actual conclusion in view, though: this impact probably didn't cause most of the extinctions happening around that time. We need evidence against that claim, not a complete history of dinosaur extinction.
Working the answers
- A
Those species were already extinct. They aren't the species whose disappearance around the time of this impact we're trying to explain. Even if most dinosaur species disappeared earlier, this asteroid could still have caused most of the later extinctions discussed in the argument.
- B
This tells us what affects crater size. It doesn't tell us that the Chicxulub impact had wider effects than the other impacts or that it caused the extinctions in question. Knowing that both size and force matter doesn't, by itself, establish the missing comparison of consequences.
- C
The author already accepts that an impact kills many nearby organisms. Finding some dinosaurs that it killed is consistent with that concession. We need a reason to doubt the conclusion about most of these extinctions, and some confirmed deaths don't settle that larger issue.
- D
We don't need a second asteroid to challenge the argument. The question is whether this impact caused the extinctions. The lack of evidence for another equally large asteroid doesn't tell us how extensive this one's consequences were.
- ECorrect
This takes a different route from my prediction: perhaps the impact didn't need worldwide effects. Most of the world's dinosaurs were living in or near the area where it struck.
The author concedes severe local damage. If most dinosaurs were concentrated in that local area, the concession becomes much more important. A catastrophe confined to that region could still devastate the dinosaur population and help explain widespread extinctions. We don't have to establish an effect on every distant continent.
E says most dinosaurs, not every dinosaur, and it doesn't specify the location of every species. It therefore doesn't prove exactly which species the impact eliminated. But it directly challenges the author's reason for dismissing the impact: limited geographic reach is less reassuring when most of the relevant animals lived within that reach.
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