Text 630, 251 rader
Skriven 2004-11-03 05:57:00 av Tinyurl.Com/uh3t (1:278/230)
Ärende: Re: Metabolism Forced
=============================


> From: Brett Aubrey <brett.aubrey@shaw.ca>
> > I disagree. Once a simple chemical replicator takes hold of the
> > chemistry of the ocean, basically dominating it, it's relatively simple
> > for that to eventually evolve, perhaps by getting slightly modified or
> > combined with other chemicals, perhaps by inducing a parasitical
> > replicator which replaces the original.
> Easy for you to say.  So do it in a lab if it's so relatively simple.

The key is "relatively". I.e. compared to starting the first replicator
(with fecundity greater then one hence exponential growth), which is
still a big question. The millions of years required are far beyond
anything that can be done in a lab during our time. Of course in a lab
somebody could manipulate circumstances to speed it up a lot, and then
use mathematical calculations to estimate how long it would have taken
without that manipulation. Still, that takes funding, which I don't
have available.

> But isn't all this still just speculation?

Correct. At present we have ideas how abiogenesis and subsequent early
chemical evolution might have happened, but a lot of research needs to
be done to pin down the particular chemical reactions that could have
been involved. Miller-Urey showed likely natural circumstances where a
lot of pre-biotic organic chemistry would have occurred, but I'm not
aware of any detailed work done to analyze exactly what was happening
at the molecular level in those experiments. For example, did activated
chemicals spontaneously form amino acids, or did some catalyst arise
which aided formation of amino acids? If catalytic action was present,
how complicated where the catalytic pathways, like a simple pipeline,
or more like a very complicated "food web"? This speculation serves two
purposes: Give a plausability argument to oppose the "it can't possibly
happen naturally so a supernatural power must have done it" arguments.
Provide ideas for future research if funding can ever be obtained.

> You write like we *know* that a simple chemical replicator took hold
> and dominated the oceans and led to life as we know it.

No. Just that to me it seems plausable and worth researching. I try to
eliminate the false arguments against this theory, so we can
concentrate on seriously considering whether it might possibly have
happened.

> Panspermia is still a possibility, no?

Correct, but that begs the question where replication really started
first. If we say it didn't happen on Earth, it merely got seeded from
somewhere else, then we still need to speculate how it might have
started somewhere else. My personal speculation is that it started on
Mars and splashed to Earth later after it was already well established
as prokaryotic life. So the geothermal vents or UV radiation etc. that
I speculate about would have been on Mars instead of Earth, but the
same scenerios work there as well as on Earth. If it came from very
deep space, far from the Solar System, then the environment would be
harder for us to guess.

> And hydrothermal vents without dominating replicators?

Right at the vent, the environment would be too harsh for a prebiotic
replicator to survive, but near the vent where the vented chemicals
have decayed (redox/energywise) a little and the water has cooled a
little, and where the water is cycling around due to bubbling from the
vent, is where I expect most of the interesting chemistry including
catalytic activity would have occurred. My speculation is that there
are several chemical species which are in abundant supply in such an
environment, and that the first replicator would use one or more of
those abundant chemicals as fuel, and consequently that first
replicator would consume nearly the entire supply of that/those
chemical(s), leaving only a little bit of that/those chemical(s) to be
used in any other way. That's what I mean by "dominating" the
chemistry, that it dominates the consumption of one/some particular
previously abundant chemicals produced from the vent (or UV radiation
alternately). Also this one particular catalytic cycle would dominate
*all* chemical reactions at that level of complexity and beyond. The
quantity of very primitive chemical reactions, such as simply hydrogen
sulfide bubbling out, would probably be greater, but at the level of
complexity matching the catalytic cycle, any other specific chemical
reaction would be a rare chance event, compared to this one catalytic
cycle which would be grinding away in massive quantities. So if we
listed the various species of chemical reaction in descending sequence
by rate of individual reactions occurring, we'd see in the first part
of our list all but one of our listed reactions being very simple,
involving only very simple chemicals, the one exception being this
catalytic cycle which consumes some of the simple common chemicals but
involves a significantly more complicated cycle of catalysts. Note that
just before the last link in the cycle chanced into existance, none of
the catalytic reactions were particularily common, and would be far
down our list, lost in the noise of millions of other equally rare
reactions. But as soon as that last link occurs and cycle closes with
fecundity greater than one, in short time the quantity of all the
catalysts in the cycle grows immensely, and consequently the total
number of instances of reaction around the cycle grows likewise, so
suddenly these already-occurring reactions move up the list to near the
top.

> > But for a fully-formed lifeform to suddenly emerge
> > out of nothing,
> Ya came in late.  As stated before, very much *not* "out of nothing",
> I just don't know out of *what*.

I mean out of nothing that was previously replicating, hence out of
nothing (except very simple chemicals) that existed in any significant
quantities, like probably only one molecule of any such complicated
species in the entire ocean at any time and then it breaks up and
millions of years pass before one more molecule of the particular
chemical species is by chance created again. I consider it unlikely
that something "alive" in the full sense could spontaneously arise
under such conditions. By comparison, a simple chemical replicator (a
catalytic cycle/loop) has some reasonable chance of spontaneously
arising in this complicated mix of Miller-Urey reactions going on all
the time throughout the oceans but mostly near sources of concentrated
energy. So my "bet" is on the simplest replicator as the first
replicator, which would be a catalytic cycle/loop, as having the best
chance of spontaneously coming into existance during the first several
hundred million years of the Earth's (or Mars's) existance.

> As stated before, very much *not* "life as we know it today".

You previously said "I think that 2 rare, complex and overlapping
events (replication, then life) are less likely than 1 (life, which
learns how to replicate, as we know it did)."

In that quote, you don't seem to define "life" to be anything which
replicates, even a simple chemical catalytic cycle, so you must mean
something more like "life as we know it today", i.e. an explicit genome
of some kind (RNA or whatever), and biochemical pathways mediated by
enzymes. Even if you allow the very most primitive form of each of
those, you still have something much more complicated than a simple
chemical catalytic loop sitting there consuming energy and replicating
itself. Such a complicated system is much less likely to arise by
chance than a simple chemical catalytic cycle. If it takes 200 million
years to spontaneously form a chemical catalytic cycle (with fecundity
greater than one), but it takes a billon billion years to spontaneously
form a lifeform per your idea, then your event simply can't have
happened yet, whereas my event happened just fine, then over the next
several tens or hundreds of millions of years evolved into what you'd
consider life. Two small steps are much likelier than one BIG step.

By the way, I should have blatantly challenged your claim that we KNOW
that life learned how to replicate. We know no such thing! What we do
know is that life replicates. But we don't know whether replication was
already happening before the stuff passed the threshold we'd accept for
calling it "life" or not. My idea is that pre-metabolism, i.e. chains
and webs of chemical reactions decaying from the high-energy input of
volcanic vents or UV irradiated chemicals etc., came first, and then
replication came next as one particular instance of such
pre-metabolism, whereby I would now refer to it as metabolism without
the qualifying prefix, and finally mutation and natural selection
caused the replicators to evolve to what we'd accept as "life".

> Well, the topic *is* OOL, not OOSOO (Origin of Something or Other).
> So maybe we (well, you, really) need to start with a definition of
> life (I'm comfortable with my internalized, personal version).  Else
> it seems there's little point in discussing its origin.

The qnswer to all such questions is a chain of events starting with
abiotic chemistry and ending with life as we know it today. Depending
on where you draw the line between non-life and life, the short answer
to your specific OOL question is the one link in the chain that starts
with the last point of pre-life and ends with the first point of
true-life.

I personally prefer to have two such dividing lines: First a definition
of what constitutes just barely life, which would be *anything* which
consumes resources (materials and energy, usually the two together) and
applies the energy to use the materials to build more of itself, such
that so long as plenty of resources are available it makes more of
itself faster than it decays, i.e. has fecundity greater than one, i.e.
any successful replicator. Second a definition of what constitutes
fully genomic evolving life, i.e. it carries some message defining how
to make more of itself and how to carry on all support activities
necessary for such replication, and such message has some sort of
alphabet such that variations in the character at some particular point
cause variations in coding for the support activities, and such that
the message is almost exactly replicated itself so as to carry almost
exactly the same message down to succeeding generations.

Once that second point has been achived, Darwin's theory explains
nicely how such life could evolve to the earliest prokaryotes we know
of, and how those could evolve to all the various forms of life we know
of today.

Between the first and second points, I've proposed mechanisms whereby
simple chemical replicators can evolve to eventually achieve fully
genomic evolving life. So if your definition of "life" includes only
fully genomic evolving life, then that part of my speculation is a
theory of OOL as you define L.

Before the first point, I've proposed mechanisms whereby the first
chemical replicator, a catalytic loop/cycle, might spontaneously form.
So if your definition of "life" is any successful replicator
whatsoever, then that part of my speculation is a theory of OOL as you
define L.

If your definition of "life" draws the line somewhere in the middle
between those two definitions of mine, then somewhere in the middle of
my speculations about how the first replicator could evolved to become
fully genomic evolving life would be the OOL per your midway definition
of L.

Note that the whole chain involves OOSOO followed by evolution of that
to become L where that last part would be the OOL theory.

Regarding cell death after oxygen is deprived:

> About how long does this take?

Human brain cells take about 7 minutes before they die.
Other human cells take longer, I don't know how much longer.

> At some time T, there was nothing we would consider "life" on this
> planet while at time T' there was.

All of us, except Gaiaists, would agree that before the first
successful replicator there was nothing whatsoever we'd remotely call
life. Most of us would agree that as soon as a prokaryote was
reproducing, that was surely life. Between those two points there's a
wide range of times various of us would say there wasn't life then
there was. My speculations haven't completely bridged that very long
gap from no-successful-replicator to prokaryotes. I've mostly tried to
bridge the early part, from no-successful-replicator to fully genomic
evolving life that was a distant ancestor of prokaryotes. I haven't
tried to bridge from the earliest fgel to prokaryotes. Anyway, the time
involved is a few hundred million years, eleven hundred million years
at the most. As to how long each of the individual links took, within
that total time for the whole chain, we at present have no idea.

> I just don't think the replicator sounds too convincing

You don't believe it remotely possible that over a time span of
hundreds of millions of years, with Miller-Urey experiments going on
constantly throughout the oceans of Earth and Mars, that sometime
during all those experiments a simple chemical replicator, possibly a
catalytic loop, with fecundity greater than one, might form by
accident? Or you don't belive that such a simple chemical replictor,
once formed and exponetially grown to have so many copies that it
persists indefinitely, could then evolve within a few additinal hundred
million years to fully genomic evolving life? Or you belive the
accidental creation of a fully formed RNA replicator or other more
lifelife replicator would happen sooner than a simple chemical
replicator (that's absurd in my opinion!!)? Or you consider *all* the
proposals for OOL to be so grossly improbable that you don't accept any
of them even as just-so speculations? Or what?
---
ū RIMEGate(tm)/RGXPost V1.14 at BBSWORLD * Info@bbsworld.com

---
 * RIMEGate(tm)V10.2á˙* RelayNet(tm) NNTP Gateway * MoonDog BBS
 * RgateImp.MoonDog.BBS at 11/3/04 5:57:44 AM
 * Origin: MoonDog BBS, Brooklyn,NY, 718 692-2498, 1:278/230 (1:278/230)