[FoRK] Water != Life (other solvents may work too)

Eugen Leitl eugen at leitl.org
Mon Jan 31 02:11:35 PST 2005


On Sun, Jan 30, 2005 at 10:02:00PM -0500, damien morton wrote:

> Even the notion that you need chemistry for life is suspect.

Are we talking naturally emerged, or designed? Designed indeed doesn't
require chemistry, see ALife.
 
> In my mind, all thats needed is a substrate that supports enogh compelxity.

For natural processes, we seem to be stuck to condensed phase.
Gas and plasma doesn't support persistent structures. There might be life
based on strange/dark matter, but we currently have no evidence that's
possible.
 
> Theres probably all kinds of environemts where that can happen.

Not really, natural element abundancy is basically the same across the
universe (local variation in metallicity currently favor the light regime),
so there are not many solvents available.

You need polar solvents, so liquid hydrocarbons are right out. This leaves
you with water, ammonia and *maybe* hydrogen sulfide. Water is special
because of 4 C anomaly, and wide liquid range (look up the phase diagram of
its close cousins, the difference is dramatic). Also, rate of chemistry at low
temperatures is glacially slow (Arrhenius equation).

Titan is certainly interesting inasmuch prebiotic chemistry is concerned. It
might even have life in its volcanic hot spots (relatively hot, liquid water
lava is pretty balmy). But, I think Europa has a far better chance of bearing
primitive life. Notice Europa would be barren, if its oceans were liquid
ammonia. Earth would be also likely barren, or only bear primitive life if it
wasn't for the water anomaly.
 
> Greg Egan is the sci-fi writer who explores this best (IMO).

Greg Egan's physics is frequently b0rken.

-- 
Eugen* Leitl <a href="http://leitl.org">leitl</a>
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