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
Scientists know what life on Earth looks like, so that’s what they’re looking for. Practically all life on Earth needs water, so if a planet has water, scientists can say that the planet could potentially harbour life (as we know it). They’re also looking for free atmospheric oxygen because it’s highly reactive and won’t remain atmospheric for long unless it’s being replenished through a biological process.
You’re asking why won’t scientists look for something else that they know nothing about. It may not even exist. If a process exists that allows for life that doesn’t require any nutrients, we have no idea what it could be. How could we possibly look for it?
We are looking for life we were exposed to – water based. So far we have not encountered any other variant hence we are looking for what we know works
They key point is that water is essential for “life as we know it”, so we’d look for it when looking for life.
It may not be necessary for a hypothetical “life as we don’t know it” but we aren’t looking for that, because we don’t know what it looks like.
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.
It doesn’t prove life on other planets. We know other planets/moons have liquid water but (likely) don’t have life. It helps guide us in the search for life though!
Life on Earth does indeed need water, even if you don’t live in it. More than that though, we know thats where life on our planet started from. Our planet is a small sample size — 1 —, but it’s all we have. What else would we be looking for from so far away? We can’t look for all the potential indicators of a different kind of life that we don’t know about.
>Why do scientists looks for water on other planets to prove life?
Because it is easier to look for life as we know it because we know so much about it. How would we recognise the signs of silicon based life forms? What would we look for? What signs would we be looking for to detect a ET that eats space rocks?
Everything above and also in earth almost all the places that has liquid water has life (-20c ~ 120c). Scorching hot water springs and coldest ice blocks has living organisms. If we find liquid water out of earth without life that would be quite a surprise as well.
Let’s say that I give you some coloured wooden blocks. Cubes are green, spheres are red, cones are blue.
Now I give you a sealed bag with wooden blocks and ask you, without looking into the bag to pick a red block. What do you pick first?
Sure, the bag might have red cubes or cones, but for all you know spheres are red. So you start with what you know.
There might be unlimited types of life out there but as far as we know, water helps support life. So we start from there.
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