On 9/01/2011 3:19 AM, Warp wrote:
>
>    It's hard to imagine how life could form without water.
>

I'm familiar with the view that water is important and perhaps essential 
for life to develop and survive.  It may well be correct or at least the 
most likely environment for life by far.

But it is interesting to think about what truly different environments 
might mean to life.

Rather than define liquid water as the essential requirement for life, I 
think the criteria might be more like:

a) A medium that provides both persistence and variability with enough 
complexity to support non-trivial patterns of organisation
b) An energy gradient that is neither too small nor too great for 
whatever the medium is - at least in some local regime for some period 
of time
c) Time

Given those factors it is possible to imagine life in all sorts of 
situations where liquid water is not an important factor.

There isn't anything in the meta-mechanism of evolution that requires H2O.

Then there could be forms of life that started in a water rich 
environment but evolved beyond that requirement.

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