PrepTest 140, Section 2, Question 24
Biologist: Scientists have discovered fossilized bacteria in rocks(72 more words not shown)
Which one of the following(31 more words not shown)
- AIt is a(24 more words not shown)
- BIt is a(32 more words not shown)
- CIt is a(33 more words not shown)
- DIt is a(24 more words not shown)
- EIt is a(31 more words not shown)
Reading the argument
The bacteria were already complex when they became fossils. The biologist takes that complexity as evidence that their evolution had started much earlier.
How much earlier? The passage gives Earth's age as about 4.6 billion years and the fossils' age as about 3.5 billion years. That leaves roughly 1.1 billion years between the planet's formation and the fossils. The author reasons that a long evolutionary history before the fossils pushes the beginning of life back toward Earth's harsh early conditions.
We could question how long that history had to be, or whether conditions elsewhere resemble early Earth in the relevant ways. But this question asks what the claim about a long history does in the argument. It receives support from the bacteria's complexity, then supports the early origin of life. That early origin, in turn, supports the final suggestion about life arising under difficult conditions elsewhere in the universe.
What we’re looking for
Follow those steps separately. A claim can be supported by one part of an argument and then serve as support for another; it doesn't have to be either an unsupported starting point or the final conclusion.
Working the answers
- A
There is support: the fossils indicate that the bacteria were complex, which the author uses to infer a long evolutionary history. The claim also helps establish further conclusions rather than merely illustrating the final suggestion. A misses both relationships.
- B
This gets the later chain right but incorrectly says no support is provided for the target claim. Complexity is the stated reason for inferring that the bacteria already had a long history.
- CCorrect
The target claim has support, and it supports another claim that supports the overall conclusion. First comes bacterial complexity; then the long evolutionary history; then life arising soon after Earth's formation under harsh conditions; finally, the possibility of life arising under difficult conditions elsewhere. C captures the target claim's place in that sequence.
- D
The target claim does support something else. A long history before fossils formed 3.5 billion years ago helps the biologist push life's origin closer to Earth's formation. D would wrongly stop the reasoning at the target claim.
- E
There are two later conclusions, but they aren't independent. The claim that life arose under harsh conditions on early Earth is itself evidence for the suggestion about difficult conditions elsewhere. E says neither later conclusion supports the other, which breaks the actual chain.
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