Logical Reasoning

PT103 · S1 · Q22 When a planetary system forms

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When a planetary system forms, the chances that a planet capable of supporting life will be formed are high.

Conclusion

The chances that intelligent life will emerge on a planet are low.

Evidence

Planetary systems are unlikely to have any large planets, and without large planets like Jupiter and Saturn (whose gravity protected Earth from being frequently struck by comets), intelligent life would never have arisen on Earth.

Evaluate

We start with counterevidence ... when a planetary system forms, the chances it will have a planet capable of supporting life are high. The reason the author concludes pessimism for the change of life emerging is because she's worried that w/o big planets to provide comet-protection services, this life-eligible planet will get pummeled with comets and not be able to have long enough periods of stability during which intelligent life could evolve.

If we're playing Devil's Advocate and arguing that these life-eligible planets would actually be likely to develop intelligent life, then we need a different means for them to get protection from comets.

Goal

Look for an answer that would give you a way to say that, .

22.

Knowing which one of the following would be most useful in evaluating the argument?

  1. whether all planetary systems are

    Out of Scope Comparison

    It doesn't make any difference whether all planetary systems are formed from similar amounts of matter. Whether there's 1 billion tons of matter or 1 trillion tons of matter doesn't change the logic riddle of, "How can you be safe from comets, if you have no large planets around?"

    3% picked this

  2. whether intelligent species would be

    Out of Scope

    This is about whether intelligent life would survive a comet strike, but the argument is about whether comet strikes would keep intelligent life from having ever developed. Also, it's pretty fair to say that from the claim that "had Earth been frequently struck by large comets, intelligent life would have never arisen on Earth" that we're already pretty clear on the impact of comets on Earth (no pun intended). If comet strikes, bad for life. We're not going to object by saying, "getting hit by comets is fine". We're hoping to object by saying, "these planets aren't going to be hit by comets ... [for some reason]."

    24% picked this

  3. whether large comets could be

    Irrelevant Distinction

    The author is talking about planetary systems that have ZERO large planets, so the distinction between 1 vs. 2 is irrelevant.

    5% picked this

  4. Correct

    how high the chances are

    Why this is right

    This answer has a potential answer that would Weaken the argument, so it's correct. If we said "the chances are very low that a planetary system will contain many large comets", then that would badly weaken the argument. This is our way to argue that "even if these life-eligible planets don't have a large planet protecting them from comets, they're still safe from comets for some reason". The reason it gives is this: there aren't many large comets in their planetary system, so they don't need a large planet to protect them.

    Skill tested: Evaluate · how this choice captures the argument's function is the move to repeat next time.

    59% picked this

  5. how likely it is that

    Irrelevant Statistic

    If only 10% of planetary systems have a large planet, that's how the author is making her argument. It doesn't matter if we take that 10% and say, "Yeah, author, but 90% of those have Earth-size planets!" The author would just be like, cool, that's still 90% of 10%! That's only 9 out of 100 planets.

    9% picked this

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