Passage Summary: Some people think life came from space because it couldn't have started on Earth so quickly. The astronomer says they're wrong because they haven't proven space-life is real; they've only tried to disprove Earth-life.

Conclusion: The extraterrestrial-spore hypothesis is likely false.

Reasoning: The proponents of the theory only argue against the Earth-origin theory; they haven't provided positive evidence for their own theory.

Analysis: The astronomer is committing a classic 'absence of evidence' fallacy. Just because a theory hasn't been proven true (lack of positive support) doesn't mean it is false. Furthermore, the astronomer ignores the possibility that disproving a rival theory (Earth-origin) could actually serve as indirect evidence for the alternative. Look for an answer that points out the astronomer is confusing a lack of proof for a theory with proof that the theory is wrong.