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As title says. We find water on a planet, and we assume that it's more likely life is there. How/why is this the case? Isn't it possible some life could survive without water? Even if the answer is 'no', the fact there's water doesn't mean life could've 'started' does it?

I'm obviously speaking with regard to the latest Mars findings, but the question is bigger than that.

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    $\begingroup$ Most living things on Earth are made primarily of water. Water is an excellent solvent of solids and gases, and is miscible with many other liquids. For those reasons it can transport chemicals to the tissues of living organisms, and provide a good medium for many chemical reactions to happen in. It is possible that life that evolved in another environment uses a different solvent / chemical transport medium, but few could be as good for the job as water. $\endgroup$ – Andrew Thompson Sep 29 '15 at 15:02
  • $\begingroup$ In the search for life, they look for water. I think one of the biggest reasons for that is life we know of requires water. Could there be some other kind of life that exists without water? Sure, but we don't know what kind of life that would be, and we wouldn't know how to find it. Scientists look for water, because that's what they know. It's easier to find what you understand than what you don't understand. $\endgroup$ – duzzy Sep 29 '15 at 18:30
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    $\begingroup$ Its the only common denominator in any life we've found it before $\endgroup$ – Premier Bromanov Sep 29 '15 at 20:39
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From a biochemical standpoint, we don't know of any life that doesn't require water. Everything on earth requires water as the solvent to a majority of the chemical reactions occurring within it. Without water those reactions don't happen and the life form dies.

However, that certainly doesn't make life based on other solvents impossible. There is always interesting discussion about silicon based life, but the seeming reason we are carbon based is due to the stability of carbon compounds vs silicon compounds in water. There could very well be another solvent in which silicon makes more stable bonds and then perhaps life would be based around it.

Aside from that, another common potential solvent in our solar system is methane, which is liquid on Titan. The problem is that for methane to be liquid, it has to be so cold that it would take a very long time for life to evolve (if it could). So we look to the water oceans of Europa more than the methane oceans of Titan.

In summary we look for water because water based life is the only we know. But we cannot rule out the possibility of other forms of life.

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Everywhere on Earth that we find water, we find life. From deep in the crust, to under the Antarctic ice sheets, to the most salty locations on the planet, life seems to follow water. The thought is, if it applies to Earth, it might apply to other planets. Of course, no one has observed life on another planet, so there is not knowing for certain if indeed water= life outside of Earth.

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