PrepTest 138, Section 3, Question 17
The conventional view is that asteroids strike the(75 more words not shown)
Which one of the following,(11 more words not shown)
- ASeveral asteroid strikes(26 more words not shown)
- BIf asteroids repeatedly(29 more words not shown)
- CThe impact craters(21 more words not shown)
- DLumpy masses within(16 more words not shown)
- ENo similar pattern(13 more words not shown)
Reading the argument
A ring of impact craters is interesting. Does it show an organized process, or are we reading too much into a pattern?
I'd want to know how substantial the pattern is. A handful of impacts might be easier to explain by chance than a very large collection arranged the same way. And if the craters appeared around the same time, perhaps the incoming objects traveled together. We need an explanation for the pattern, not just a description that sounds striking.
What we’re looking for
The geophysicist says asteroid impacts result from a highly organized natural process, rather than simply striking at random locations. To support that claim, I'd look for something that explains why incoming asteroids would be directed along particular paths. I don't yet know what that mechanism would be.
Working the answers
- A
This explains how impacts could contribute to mass extinction: volcanic activity and blocked sunlight could disrupt life. But strikes could have those effects whether their locations were random or organized. A concerns the consequences of impacts, not the process directing them.
- B
This starts by supposing that asteroids repeatedly hit the same spots, then describes a possible effect on molten rock and continental movement. It doesn't explain why those repeated strikes would occur. An effect of impacts doesn't establish the organized process alleged to cause their locations.
- C
A single incoming cluster could help explain why this group of craters has a pattern. But it doesn't establish the broader claim about a highly organized natural process directing asteroid impacts. It gives us a shared arrival for this group without the directing mechanism D supplies. We shouldn't go further and say C proves the locations were random; it doesn't do that either.
- DCorrect
This supplies a mechanism that can organize the incoming paths. Masses inside Earth interact gravitationally with approaching asteroids and force them into specific orbits before impact. Now there is a natural reason for the paths, and therefore impact locations, to be constrained instead of random. That directly supports the geophysicist's claim.
- E
If this is the only period with such a pattern, we don't gain evidence that an organized process generally governs impacts. It makes this pattern look exceptional. A unique pattern doesn't prove randomness, but it also doesn't provide the mechanism or wider support the geophysicist needs.
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