What dictates that extra terrestrial life requires water in the same way as we do? Even on earth we have fish who can’t live in the open air, and people who can’t live underwater.
What is to say that ET can’t eat space rocks to obtain all of its nutrients, or even more, what is to say that they require nutrients at all?
Edit: Thanks for all the wonderful answers. Makes perfect sense. They aren’t so much saying we HAVE to have water to create life, more that we only know how that works and looking for the unknown in the vast expanse that is the universe would be the worlds largest needle in a haystack game.
In: Planetary Science
We don’t know what forms life could possibly take, but we have exactly one example of life that certainly exists.
That example requires water.
So if we are looking for “life as we know it” looking for water is a good bet.
Life in the end just is a question of self replicating patterns. This in theory could take all sorts of forms, but chemistry of self-replicating molecules is one that we know for sure is a thing.
Those molecules probably require some sort of solvent to be suspended in.
Water is a good bet. For one thing water is extremely common.
Alternatives may include Ammonia instead of water.
We don’t know how life that evolved in an ammonia ocean would work in detail or if it would even be possible at all.
A life based on rocks has been often proposed in sci-fi. Rocks are mostly made up out of silicon compounds and silicon is directly one level below carbon in the periodic table and froms similar compounds to it. Silicon based life has the problem though hat it doesn’t easily form the same sort of long strings of molecules that our life is based on. It would also require some sort of solvent for the hypothetical silicon based self-replicating molecules to be suspended in. That would most likely be water too.
So if there is a rock eating ET out there they likely also evolved in a world with liquid water.
Other solvents could work, but water is much more common in the universe.
We do know water works is incredibly common and works so we start with that with that as a basis.
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