PrepTest 118, Section 1, Question 21
Although the geological record contains some hints of(58 more words not shown)
Which one of the following(9 more words not shown)
- AIf there were(22 more words not shown)
- BMajor meteor impacts(17 more words not shown)
- COf the mass(25 more words not shown)
- DIf there is(22 more words not shown)
- EThere could be(25 more words not shown)
Reading the argument
What does “consistent” mean here? If it means that every major impact must bring a mass extinction, the record described gives us a problem. But if impacts sometimes cause extinctions, exceptions wouldn't by themselves erase that connection.
The record points to both kinds of exception: extinctions without a known major impact, and major impacts without an apparent mass extinction. The first could reflect other causes, such as disease, volcanic activity, or an ice age. The second could mean that an impact's consequences depend on other circumstances. We shouldn't invent those circumstances as facts, but we also shouldn't assume every impact must have the same result.
Imagine impacts brought extinctions 20 percent of the time. That wouldn't be a 100 percent rule, but we'd still want to know what caused the extinctions in those cases. Simply saying “not every time” doesn't settle what kind of causal connection exists.
What we’re looking for
The question asks for an assumption that makes the conclusion follow. We need a rule connecting the exceptions to the claim that there is no consistent causal link. In particular, a rule requiring every major impact to be followed by a mass extinction would do the job: the record says that requirement isn't met.
Working the answers
- ACorrect
This defines a requirement for the consistent causal link: all major impacts would have to be followed by mass extinctions. But the record contains major impacts that apparently weren't followed by them. Given A, those exceptions are enough for the argument to conclude that the record suggests the absence of a consistent causal link.
Read the rule through the failed requirement. If the link requires every impact to produce an extinction, and that pattern isn't present, the claimed consistent link cannot be present on that account either. We don't need the answer to start with the evidence to use it.
- B
This requires many extinctions after impacts, not an extinction after every impact. The evidence doesn't establish that the many requirement fails. There could be many examples of the connection and also many exceptions. B therefore doesn't let us rule out a consistent causal link from the exceptions described.
- C
This helps address a different uncertainty: perhaps extinctions with no known preceding impact were actually preceded by impacts that left no recorded hints. C largely rules that possibility out. But other causes of extinction could exist alongside a consistent effect of major impacts. C still doesn't tell us what pattern is required for a consistent causal link, so it doesn't make the conclusion follow.
- D
This tells us what follows if there is no consistent link. We are trying to establish that there is no consistent link in the first place. Observing its stated consequence doesn't establish that starting claim; the same observation could occur when other causes of extinction exist. D gives us the connection in the wrong direction for this argument.
- E
This explicitly allows a consistent causal link despite some impacts not producing extinctions. That leaves open the very possibility the argument needs to exclude. E weakens the proposed move from exceptions to no consistent link instead of making that move valid.
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