"Brett Aubrey"  wrote in message
news:ciqvp3$1tv3$1{at}darwin.ediacara.org...
"TomHendricks474"  wrote in message
news:civ2db$2rm$1{at}darwin.ediacara.org...
> >> > IMO the more we know about life, the more we
> >> > will see how locked in it is to certain conditions.
> >> > Sci-fi lets' us imagine anything as does early
> >> > unproven speculation. But as the origin becomes
> >> > deciferable, we'll find it limits what life is
> >> > and where it can be, much much much more
> >> > than most think now.
> >>
> >> Interestingly, the last few decades has taken the opposite
> >>direction.  Extremophiles are now found deep in the rocky
> >>mantle, high in the atmosphere and around oceanic vents,
> >>where we used to assume life was impossible.  If life has
> >>evolved elsewhere, I think we'll find it can thrive in even
> >>more extremely diverse and "inhospitable" (from our
> >>viewpoint) habitats than ones just here on this planet.
> >>If I were a betting man and thought that any of this
> >>can be proven in my lifetime, I'd even propose a
> >>wager that whatever life we find will not have DNA,
> >>nor anything we'd consider a variant, as its base.
> >>Regards,  Brett.
>
> TH
> I don't think so. The extremophiles on planet earth took
> 4 billion years to evolve that ability.

I wasn't aware of this, but naiively assumed they've inhabited these niches
for much (most?) of the past 4BY.  How sure are you about this?

> Our common
> ancestor probably was formed in a very specific
> set of circumstances that began with a heat cycle
> and water in liquid form (which limits the heat cycle
> to an amazingly short short short temp range - and
> if its also a wet/dry cycle, then we are left with
> an almost exact temp range of near 100C to allow
> for water and steam both.

I don't dispute any of your probability (my earlier post stated "I think
you're likely right about the heat cycle"), but think that unless life is
extraordinarily rare (and barring panspermia) that there will likely be
more that a double-helixed, quad-spanned (my whuffo-like term)
nucleic acid as the only possible basis of an evolutionary mechanism.

> Further an important clue is that nucleic acids
> absorb UV at 260nm. IF that is indeed a key
> element then life is almost point-on specific.
> Your scenario of anything goes would have to be
> supported by some 'for instance' before I would
> change my mind on this.

To clarify, there wasn't an "anything goes" scenario.  I stated, rather
"(there will not be an infinite variety of chemicals that can produce life,
but there's probably >1 - a wild guess.)"  and  "I'm suggesting that you
can't know that Earth's (raw materials and) chemistry is the *only* one
capable of producing life."  (emphasis added.)

And I won't grasp at 'for instances', partly because, as stated, "I'm not
thinking that we can even guess at what that might be"  and  "we'll likely
never know".  I'm also not trying to change your mind, but was only
providing your requested comments.

However, I will suggest that when people have argued for limitations such as
life can only take the one form it has taken here on Earth, (or "we'll never
fly"; "we'll never get to the moon"; "all that can be
invented has been
invented", etc., etc., etc.) the limitations are frequently proven invalid.

> -----
> >I completely agree on all points, Brett. It may well turn
> >out that the primary criterion for life is the necessity for
> >complexity, and it may be achieved over many paths and
> >materials.     ...tonyC
>
> TH
> Again that is hard to support with facts.

There is a dearth of facts around OOL, it seems to me.

> The complexity
> comes from ways to survive the heat cycle IMO.
> So life is not a first event, it is a reaction to what
> comes before it. You can't begin in the middle of the
> process. Life cannot come before certain earlier
> instances.  Life cannot exist without the  heat cycle
> that produces the monomers for it, stirs the
> primordial soup pot, powers it with endless cyclic
> energy in a reasonably constant form (with enough
> variation to make variants and have some variants more
> stable - that lead to even more stable variants) and
> selects some variants over others through UV damage, etc.

But none of this says DNA (or variant) is the *only* way or
that "other forms" of life are impossible.
Regards,  Brett.
---
þ RIMEGate(tm)/RGXPost V1.14 at BBSWORLD * Info{at}bbsworld.com

---
 * RIMEGate(tm)V10.2áÿ* RelayNet(tm) NNTP Gateway * MoonDog BBS
 * RgateImp.MoonDog.BBS at 9/24/04 5:56:08 AM