Text 780, 77 rader
Skriven 2004-11-13 02:49:00 av Tinyurl.Com/uh3t (1:278/230)
Ärende: Re: First Mutation Was Bi
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> From: "John Edser" <edser@tpg.com.au>
> What is missing but _absolutely_ required is
> a _refutable_ theory, i.e. not just another
> theory that can only be tested to non verification,
> re: how a replicator can be caused initially
> and how it might be able to sustain itself
> long enough to become our most ancient
> ancestor.

It's too early to make a theory for the whole process, because we don't
yet have enough data to decide whether capable replicators are created
so often (under Miller-Urey-type conditions) that there already was a
successful one in the original Miller-Urey experiment but we didn't
look for it so we didn't notice it, or whether capable replicators are
created less often but still common enough that with the whole ocean
available they happen within a year, or whether they require hundreds
of millions of years even with the whole ocean available, or whether
they have only about one chance in a million of occurring at all in a
billion years of each planet so most likely Earth was seeded from some
lucky planet elsewhere in our galaxy, or whether they occur so
extremely rarely that there probably hasn't been one in the entire
history of the whole Universe, in which case I'd have to scrap this
scenerio for how abiogenesis happened.

At present the most that is reasonable to theorize are just initial
pieces. For example, there's a theory that the early Earth was
subjected to UV bombardment from an early Sun, frequent crashes of
comets/asteroids, and lots of volcanic activity including lots under
the water as soon as the Earth had cooled enough to permit liquid water
on the surface. There's no way you can test that in the lab, because
it's history, but by studying other planets around other stars we can
get an idea whether this theory was likely to be true or not in Earth's
case.

Depending on that, there's a theory that such radiation and heat
sources caused simple molecules (water, carbon dioxide, methane,
ammonia, etc.) to break apart, and that these fragments of molecules
initiated cascades of chemical reactions. This we *can* test in the
lab. Furthermore we can learn which specific cascades occur and what
the reaction products are at each stage of the cascade until we reach
molecules that are so stable that no further reactions are likely for a
long time without new input near the start of the cascades. Once these
experiments are done, we could make a more detailed theory that lists
the various chemical species and their position within the cascades and
their yield (quantity produced) under various conditions (initial mix
of simple chemicals, type and intensity of energy input, temperature,
etc.).

Extending that work, we can then learn which chemicals created in this
way have catalytic activity, what kind and strength of catalytic
activity, what quantity of yield relative to speed of destruction of
the catalyst, and thereby compute one-step fecundity of each catalyst
to each of its reaction products. (I would hazard a guess right now
that it takes less than a year for a catalyst to be produced somewhere
in the ocean under primitive conditions such that it has one-step
fecundity greater than one for some reaction product that is rarely
produced by non-catalytic means. Note that it's impossible for a
non-catalyst to have one-step fecundity greater than one, unless you
use tricky accounting such as counting an input dimer just once but
then cleaving it and counting the total of monomers which would be
twice the input minus any loss.)

So do you know of any of that lab work, or simulation on computers,
that is already occurring, and any results reported? I don't have
access to any university library that would have such reports, just a
public library with SCIENCE where I haven't yet seen any such, but I
don't browse every issue before they expire from the 3-month shelf, so
I could easily have missed it.
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