Text 708, 119 rader
Skriven 2004-11-08 21:33:00 av Tinyurl.Com/uh3t (1:278/230)
Ärende: Re: Metabolism Forced
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> From: tomhendricks474@cs.com (TomHendricks474)
> I think the key is what powered the first replicator

The same thing that powers the Miller-Urey type of experiments:
Molecules are ionized or torn apart by a high-energy source, either UV
or extreme heat (from volcanic activity, crashed meteor/comet, or
lightning). These start a cascade of subsequent chemical reactions with
anything they touch, with reactions near the start of the cascade
spontaneously happening almost immediatley, and reactions further from
the start having a slower reaction rate so they might sit in a
meta-stable condition for a relatively long time.

> For those schooled in darwinian evolution - we stretch things to get
> to first replicator , because we understand the rest.

Well we consider the step from lots of interesting chemical activity in
those cascades of chemical reactions, to the first replicator, as the
only "missing link", everything else being pretty well worked out to or
confidence it'd really happen. So we spend most of our energy trying to
fill in that "missing link" so the path from non-life to
life-as-we-know-it would be unbroken.

> There is yet no reason why any aspect of life would have emerged on
> its own for any reason.

That sounds rather circular or redundant or somesuch. Per my
speculations, the first replicator didn't emerge for any reason other
than the fact the conditions suitable for formation of the first
replicator were present and enough time passed in that kind of
condition for the first replicator to chance into existance. The key
fact we don't yet know is the statistics (per unit time) of lengths of
chains (of once-through fecundity greater than one) of catalysts which
spontaneously appeared in the pre-life oceans. Two other key facts
aren't personally known by me, but are probably known by somebody else:
The number of different kinds of catalyzed reactions, and the
statistics of chemical species in an equilibrium situation after a
Miller-Urey experiment has run long enough to reach equilibrium. As
soon as the length-of-chain statistics are learned, and that's put
together with the other two key items of info, we'll be able to
estimate how often capable replicators are spontaneously created, and
one more mathematical step (see my posting a few minutes ago in another
thread) takes us to the length of time to expect to wait before the
first capable replicator succeeds at surviving the first few tens of
generations to where there are so many copies of it that it won't go
extinct for a very long time, and only when replaced by a new species
of life derived from it.

> The irreducible complexity of genetics-first origin scenarios is
> high, requiring joint emergence of catalysis, compartmentation, and
> heritability to make the minimal self-perpetuating structures.

No. There's only one thing going on, per my catalytic-loop scenerio: A
chance creation of a single molecule of a catalyst yielding a catalytic
chain (of once-through fecundity greater than one) long enough to close
on itself, happens every so often. Each time it happens, there's about
a 50% chance that over the first several tens of generations it'll grow
to many many copies rather than die out. So after some rather small
number of instances of such a capable catalytic loop, one of them is
successful. Voila! The first just-barely-life. Nothing irreducibly
complex about that at all.

There's no compartmentation, no variation in heritability, just this
replicator making more copies of itself at an exponential rate. Since
the thing being catalyzed is the catalyst itself, there's only one
thing going on, not two things, but you're calling it two things to
make it sound more complicated than it is. catalysis and replication
and inheritance are all the same thing here. What is inherited is the
particular set of chemical species which are in the loop. What is
replicated are those same chemical species. That is catalyzed is the
production of those same chemical species. See, only one thing going
on, nothing complex at all.

> life did not emerge, it is a planetary chemical response to a non
> random heat cycle (with further restrictions)

You haven't explained how a simple heat cycle could cause a wide
variety of chemical reactions to occur, whereby some replicator might
chance into existance eventually as a result of some random one of
those reactions. Has anybody ever run a Urey-Miller kind of experiment
where there is *no* input of ionizing or chemical-breaking-apart
energy, merely a smooth temperature cycling over a reasonable range
(say from near freezing of water to near boiling of water)? I predict
such an experiment could run for an indefinite time and still not
produce amino acids or anything else interesting. Do you disagree?

> In the end you look at earth and the only things that have survived
> 4.5 billion years are life, recycled chemicals and a few grains of
> zircon!

The simple chemicals didn't survive. They simply were re-created by
random decay of other chemicals as fast as they were destroyed. There's
no direct causal relationship between simple chemicals which existed
billions of years ago and the same species of simple chemicals which
exist now. The same specific molecules from back then don't exist at
all now, except by chance if the atoms of a single molecule back then
chanced their way back together recently.

Zircons survived only because they were created once and they're so
stable they don't break down for a very long time, longer than the
Earth has existed so-far. Give them enough time and eventually they'll
all be gone. Statistically they don't survive, they decay with a very
long halflife. You should have included individual nucleons among the
things you list as having survived, especially iron nuclei deep in the
core of the Earth, because they survive indefinitely if protons don't
decay and they decay with a very very long halflife even if protons do
decay.

Life has survived by replicating, and will survive as long as
conditions in places it can get to permit replicating. Life really does
survive, not just decay very very slowly.
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