We’re assuming that alien life requires the same things we do, why?
In: Biology
Because it is necessary for life *as we know it*.
We know how to find life *as we know it* because we know that if we detect liquid water and molecular oxygen in a planet’s atmosphere, it *has to* mean photosynthesis, for example. We don’t know any similar markers for life based on other chemistries.
There might be, for example, methane and fluoride based life out there, but we world be able to detect it because we don’t know what to look for. If you don’t know what to look for, there’s no point in looking for it.
Water also has some rare properties that make it uniquely suitable for life. For example, solid water (ice) is lighter than liquid water, meaning oceans don’t freeze from the bottom up, which would be bad for life.
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