PrepTest 137, Section 2, Question 20
Astronomer: Earth was bombarded repeatedly by comets and(74 more words not shown)
Which one of the following(30 more words not shown)
- AIt is a(19 more words not shown)
- BIt is a(19 more words not shown)
- CIt is a(19 more words not shown)
- DIt is a(18 more words not shown)
- EIt is a(27 more words not shown)
Reading the argument
Mars escaped the bombardment that probably prevented early life on Earth. That makes earlier microbial life on Mars a possibility, but it doesn't guarantee there was life there. We'd still want to know whether other conditions, such as temperature and water, were suitable.
The astronomer keeps the claim tentative: there could have been microbes on Mars first. Meteorites from Mars then supply a possible means of bringing microbes to Earth. The final proposal is that Earth's life may have begun through that transfer.
What we’re looking for
The statement we're asked about sits between the evidence and that proposal. Mars's escape from severe bombardment supplies a reason for it, and it in turn helps support the suggested origin of life on Earth. So it has support and supplies support. The remaining question is whether earlier Martian life is required for this explanation or is enough to establish it.
Working the answers
- A
Some justification is provided. The contrast between Earth's severe bombardment and Mars's escape from it is offered as a reason microbial life could have existed on Mars earlier. We might want more evidence, but that doesn't mean the argument provides none.
- B
This makes two mistakes. The claim does receive justification, and the possibility of earlier Martian microbes doesn't by itself establish that they could reach Earth and start life here. The argument also needs the proposed route of transfer. B both ignores the offered support and overstates what the claim establishes.
- CCorrect
The bombardment comparison supports the possibility of microbes existing on Mars first. That possibility is required for the proposed explanation of Earth's first life: microbes couldn't have arrived from Mars to start life on Earth unless microbes could already have existed on Mars.
This doesn't mean we've proved there actually was Martian life. The argument proposes a possible origin, and the earlier-life possibility is a needed part of that proposal. C captures both its supported role and its necessity for the argument's explanation.
- D
Earlier Martian microbes aren't enough. Life could have developed on Mars and separately developed on Earth, without any microbes traveling between them. Or the microbes might not have survived a journey. The claim helps the proposed transfer story, but it doesn't establish that story by itself.
- E
The claim does support the conclusion without guaranteeing it, but E goes wrong by calling it unnecessary. If earlier microbes on Mars weren't even possible, they couldn't be the source of Earth's first life. This isn't a dispensable detail; it is part of what the proposed origin requires.
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