On Extraterrestial Life

I used to think that the interest astronomers seeking life on other planets have for exoplanets in the “Goldilocks zone” that can sustain liquid water, or for signs of water in this solar system, or for signs of complex organic molecules outside Earth, that this interest is misguided. After all, they’re looking for the materials that are the building blocks of life on this planet, but it’s perfectly possible that life on other planets is made out something completely different, such as having ammonia as a substrate or having silicon as the core constituent of complex molecules (and these are relatively mild modifications, they’re building life on the same general plan and just substituting one material for another). Perhaps searching for Earth-like life is the best scientists can do given the absence of any other information on what to expect aliens to be like, but we shouldn’t think these clues are actually the right guides for finding life on other planets.

However, thinking about this more carefully, I changed my mind. Let me explain:

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