PrepTest 103, Section 1, Question 22
When a planetary system forms, the chances that(77 more words not shown)
Knowing which one of the(9 more words not shown)
- Awhether all planetary(8 more words not shown)
- Bwhether intelligent species(11 more words not shown)
- Cwhether large comets(12 more words not shown)
- Dhow high the(10 more words not shown)
- Ehow likely it(15 more words not shown)
Reading the argument
A planet that could support life may still need protection while life develops.
That makes the argument seem reasonable at first. We're told that Jupiter and Saturn protected Earth from frequent large-comet strikes and that intelligent life wouldn't have arisen here without them. If planets that provide that protection are rare, perhaps the chance of intelligent life developing on a planet is low too.
My first hesitation is about the size of the universe. Even a low chance could produce some successes when there are many opportunities. But that doesn't refute this conclusion: the author says the chance on a planet is low, not that intelligent life is absent everywhere else. We should respond to the probability claim actually made.
What we’re looking for
The stem asks what information would be most useful in evaluating the argument. I don't yet have a precise missing fact predicted. I'll look for a question whose answer would make the move from Earth's experience to the broader conclusion more or less convincing.
Working the answers
- A
Similar amounts of starting matter might be relevant to how planetary systems form, but we are already given the claims about how commonly life-supporting planets and large planets form. A doesn't directly test whether the absence of large planets generally prevents intelligent life from emerging. We'd need additional connections to make the amount of matter answer that question.
- B
Surviving a comet strike after intelligent life exists is different from intelligent life emerging despite frequent large strikes. The passage gives us a claim about the latter on Earth. A species might survive one impact even though repeated earlier impacts would have prevented its development. B doesn't directly address whether Earth's need for protection extends to other planetary systems.
- C
Perhaps one large planet can provide the protection that two provide here. That would matter if the problem were specifically the scarcity of pairs. But the premise says systems are unlikely to contain any large planets. Reducing the needed number from two to one doesn't explain how a system without either could support the development of intelligent life.
- DCorrect
Are the dangerous comets even there? That's a gap I hadn't initially noticed. Earth needed protection from frequent strikes, but another planetary system might contain few large comets and have no comparable threat to protect against.
If many large comets are common across planetary systems, the Earth's-shield example becomes more useful. If they are uncommon, the lack of large protective planets tells us much less: a planet might develop intelligent life without a shield because it rarely faces the danger. The answer to D can move our assessment in either direction.
- E
This concerns the overlap between systems with large planets and systems with Earth-sized planets. The opening premise doesn't establish that specific overlap, so don't reject E as merely repeating a known fact. Still, even perfect overlap would concern the unusual systems that have large planets. D more directly tests the argument's crucial move: whether the many systems without large planets generally need that protection at all.
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