Logical Reasoning

PT15 · S3 · Q6 As far as we know, Earth

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As far as we know, Earth is the only planet on which life has evolved, and all known life forms are carbon-based.

Conclusion

We should generate our scientific estimates of the probability of alien life from estimates of the number of Earth-like planets and the likelihood of carbon-based life on those planets.

Evidence

As far as we know, Earth is the only planet where life evolved, and the life forms are carbon-based.

Evaluate

Our job is support this recommendation. If we were going to support it with a linking idea, it would sound something like this:

all known life is found estimates of alien life on Planet X and → should be based on with property Y estimates of X and Y

How might one object to this recommendation?

We could say that even though we've only found life on Earth and carbon-based, that's not a strong reason for us to think that we should only be looking for planets like ours and life forms like ours. Maybe life more commonly emerges on planets the size of Jupiter, with silicon-based life.

Goal

Look for an answer connecting .

Or look for an answer ruling out objections like,

6.

Which one of the following general principles most strongly supports the recommendation?

  1. There is no good reason

    Opposite

    This would be a great weakener. The author is assuming a correspondence between the life we've yet to observe and the life we have so far observed.

    2% picked this

  2. A scientific theory that explains

    Unrelated to Recommendation

    This recommendation is not about picking one scientific theory over another. It's just endorsing one method of calculating the probability of extraterrestrial life.

    2% picked this

  3. It is preferable for scientists

    Weakens

    The recommendation is about how we can make a good estimate about the unobservable presence of extraterrestrial life. This answer is saying we shouldn't make estimates about unobservable things.

    15% picked this

  4. A scientific theory that explains

    Unrelated to Recommendation

    This recommendation is not about picking one scientific theory over another. It's just endorsing one method of calculating the probability of extraterrestrial life.

    5% picked this

  5. Correct

    Estimations of probability that are

    Why this is right

    This is the only answer even giving us a principle for how we should estimate probability (which is what the recommendation is about), so this answer leaps out to the lead in terms of relevance. Was the method of estimation recommended tying its estimations to what is known? Sure! It was saying, "As far as we know, life can emerge on Earth-like planets with carbon-based life forms. So let's base our estimate on those two known properties."

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

    75% picked this

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