Invisible <voi### [at] devnull> wrote:
> >    Of course for the water to be any good, it has to be in liquid form.
> > If you are too far away from the Sun, all the water will be frozen solid.
> > This isn't a very fertile ground for life to form. There are little chemical
> > reactions going on, chemicals are not very free to move, and there are
> > probably a huge bunch of other properties necessary for *any* kind of
> > life to form which just aren't possible with deep-frozen ice.

> You're aware that (on Earth) there are organisms that live in solid ice, 
> right?

  They did not originate in ice. The simply adapted to it afterwards.

> >    Now, perhaps if there was a liquid which remains an liquid form at those
> > temperatures, it could ostensibly happen. However, such liquids are both
> > extremely rare (iow. there wouldn't be enough of it in any given planet),
> > and their chemical properties are probably inadequate for any kind of
> > lifeforms.

> What makes you think that chemicals which are "rare" on Earth would 
> necessarily be rare elsewhere?

  There would have to be a significantly different process that formed
those rare elements than here on Earth. What would that process be?

  Heavy elements are formed when stars explode. After that the only way
for one element to change into another is by radioactive decay, and there's
only so much that will be formed that way.

> (E.g., O2 used to be "rare" on Earth - extremely rare, in fact.)

  O2 is not essential for life (unlike eg. water).

> > (Also, most liquids other than water get denser when they
> > solidify, which is a big problem.)

> Care to explain why?

  If water had a higher density when it freezes (as happens with the vast
majority of other chemical compounds), life on Earth wouldn't exist because
all bodies of water would freeze from the bottom up, killing all living
organisms. Water having a lower density when it freezes happens to create
a nice protective "shell" on top of bodies of water when they freeze,
insulating it from the cold. (That's why eg. lakes don't freeze solid
throughout, they only get a relatively thin layer of ice. Relative to
the entire depth of the lake, of course.)

  (Although I don't know this for certain, I'm pretty sure that if the
Earth was closer to the Sun so that it would never experience ice ages
or the like, it would be too close for life to form for other reasons.)

-- 
                                                          - Warp

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