PrepTest 142, Section 2, Question 14
Geologists recently discovered marks that closely resemble worm(40 more words not shown)
Which one of the following,(6 more words not shown)
- AIt is sometimes(11 more words not shown)
- BGeological processes left(21 more words not shown)
- CThere were some(26 more words not shown)
- DAt the place(32 more words not shown)
- EMost scientists knowledgeable(38 more words not shown)
Reading the argument
The marks look like worm tracks, but they are much older than the earliest known traces of multicellular animal life. Does “earliest known” tell us when that life actually began?
Not necessarily. Our evidence could be incomplete. The half-billion-year gap is a serious reason to ask questions, but the absence of a known older trace doesn't by itself establish that no animals existed then. I'd be interested in evidence that worms lived earlier than the existing record suggests.
What we’re looking for
The geologists instead favor geological processes. For the weakener, I'd first look for evidence that worms could have made marks this early. We need a reason to doubt the argument, so I'll test that prediction against the choices.
Working the answers
- A
Sometimes dating sandstone is difficult. Was it difficult here, and was this estimate wrong? A doesn't say. A general possibility of dating trouble doesn't establish a problem with the particular timing evidence used in this argument.
- B
Geological processes were capable of making many kinds of marks during the relevant early period. That gives us reason to consider the geologists' explanation rather than reject it. It doesn't establish that geology made these particular marks, but it supplies no evidence against that account.
- C
Another life form could matter if it existed at the relevant time and could explain these marks. But C doesn't tell us that these organisms were present half a billion years before the earliest known multicellular traces. Calling them “early” leaves the timing question open. It offers a possible resemblance without addressing the specific historical problem as directly as D does.
- DCorrect
This takes a different route from my initial guess. Instead of giving evidence for worms, it attacks the geological explanation itself. At this location, the geological processes likely to leave worm-like marks could not have occurred when the marks were made. The proposed explanation loses its likely mechanisms at the very place and time we need them.
That doesn't prove worms made the marks or exclude every imaginable geological cause. It does make the claim that geological processes probably caused them much less convincing. We can weaken an explanation without supplying the final correct explanation.
- E
Soft tissue leaving scarce evidence gives us a reason to keep an incomplete record in mind. But being among the earliest animals doesn't place worms at the much earlier date of these tracks. E leaves that half-billion-year gap unresolved. D more directly challenges the likely processes offered as the explanation for these particular marks.
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