Text 694, 79 rader
Skriven 2004-11-07 21:59:00 av Tinyurl.Com/uh3t (1:278/230)
Ärende: Re: Not Hydrothermal Vent
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(This is the last of three articles I posted this 9 days ago, via
Google Groups while I was away from my usual method of posting, which
never appeared, so I'm trying to post them again, this time by my usual
method:)
> From: tomhendricks474@cs.com (TomHendricks474)
> Hydrothermal vents are somewhat methodical, but
> they would not have lasted the millions of years
> necessary to form all the stages leading to life

It isn't necessary for a single vent to last all that time.
It's sufficient that there were many many vents all at the
same time, and that they were close enough together that
chemicals could drift from one to another, so that any replicator
that formed near one vent which consumed vent-stuff would diffuse
throughout the region and eventually colonize other vents before
the vent-of-origin ceased to exist.

> The ability of photosynthesis is in some of our
> very earliest fossil evidence.

This fossil evidence doesn't go far enough back to get close
to the time when abiogenesis is presumed to have occurred.
Whatever happened way back then is like to be much simpler
than photosynthesis. I don't accept that photosynthesis could
happen by accident, whereas a simple catalytic cycle formed
from byproducts of volcanic vents could indeed happen by accident.

> Even if meteors or comets sterilized the earth
> during this period - a. they would possibly bring in
> monomers (like the Murchison meteor) and b. the
> sun would be there to re-start the origin process.

Each time it has been destroyed and needs to re-start, all
that progress has been lost, and it's chancy whether it'll
re-start at all. But in crevices in rock near volcanic vents,
water could persist after such a global sterilization of
the open seas, and any replicator that had been produced in
very large quantities could survive enough copies to get
going again as soon as water is abundantly available again,
with no need to re-start from scratch, rather just pick up
where left-off after a brief lull in activity.

> The genetic code is IMO there because of
> the UV damage on the pyrimidine pairs - thus
> separating the two sets of bases and aligning them
> with different types of amino acids.
> Hydrothermal vents could not do that.

This may be an argument that UV influenced early evolution
at some point in time, but doesn't eliminate the chance
that life mostly developed around volcanic vents and only
evolved in a high-UV environment a minority of the time.

Maybe abiogenesis occurred around vents, then miagrated
to high-UV regions and evolved the ability to survive there,
and then such UV-tolerant creatures bred better than the
volcanic-vent creatures to the point where they drove the
vvc to extinction, so the UV-tolerant creatures are a common
ancestor of everything alive today.

The recent discovery that a common volcanic-vent chemical
spontaneously causes amino acids to link together into chains,
lends support to volcanic vents being the general locale where
the first replicator occurred. With amino acids linking together
into many many random sequences, and with a good fraction of
such sequences having some catalytic ability, the variety of
such catalysts would be very large, hence the variety of catalyzed
reactions would be very large, making the chance of a catalytic
cycle highly likely compared to chemical systems where there isn't
much variety in catalysts randomly created.
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