Passage Summary: Since Earth is one of nine planets and it has life, we can apply that same one-in-nine ratio to the billions of other planets out there to conclude that life is everywhere.

Conclusion: There is likely a massive number of planets in the universe that can support life.

Reasoning: One out of the nine planets in our own solar system supports life, and there are a staggering number of other planetary systems in existence.

Analysis: The author is making a massive leap by assuming that our solar system is a representative sample of the entire universe. For this calculation to hold any water, the argument must assume that the conditions in our little corner of space aren't unique or incredibly rare. We are looking for a necessary assumption that bridges the gap between 'our ratio' and 'the universal ratio.' If our solar system is an extreme outlier, the whole argument collapses, so the author must be assuming it is not.