Re: OOL II - Building Blocks

> From: "Perplexed in Peoria" <jimmenegay@xxxxxxxxxxxxx>
> > One scientist (forgot who) suggested that the unanalyzed tars acted
> > like time release capsules - that would replenish the soup (for those
> > of us who still think prebiotic soup was important) as the environment
> > broke it down.
> An interesting idea. Or perhaps the tars were simply recycled to CO and
> CO2 by subduction and vulcanism.

Or all of the above. In the early days, tektonic plates hadn't yet
formed, the crust itself hadn't yet formed, the topmost part of the
mantle was in contact with water hence must have been below the melting
point of rock, non-existant tektonic plates hadn't slid around and
collided and buckled to form continents, the top of the mantle was
relatively flat, so after enough water had deposited there was a global
shallow sea. At least that's what I got in my mind from various recent
theoretical studies from various sources (online and print). Assuming
that, we didn't have subduction zones like we do now, rather we had
haphazard patchwork of subduction and volcanism.

Today's subduction zones tend to swallow *everything* that is attached
to the descending tektonic plate, and swallow it *deep*, all the way
down until it melts and merges with the magma of the mantle. The only
part that doesn't make it all the way down is stuff that melts or
vaporizes early and then rises to form volcanic activity. But of course
that part is heated enough to destroy any complex organic chemicals.

But the haphazard patchwork of subduction and volcanism surely didn't
pull stuff very deep most of the time. I expect there was a wide range
of degrees of heating of material from the time it started to sink
until the time it somehow got back up to the shallow sea, all the way
from slight warming before convection brought it back up, through
denaturing double strands of polymers to make single strands and
melting globs of tar to separate the various molecules, and decomposing
polymers to monomers, and some scorching of the monomers and other
simple organic molecules, to near complete destruction of organic
chemicals with only the very stable parts such as saturated
hydrocarbons and iron-cyanide/heme complexes surviving, and finally to
complete decomposition to carbon dioxide & carbon monoxide & water
vapor & {hydrogen sulfide or sulfur dioxide or atomic sulfur} & ionic
metals&halogens. (Does anybody here know what happens to the
phosphorus? I mentally ran through the mnemonic CHOPKINS (Chinese name)
CaFe (diner) Mg (mighty good), and P was the only element where the
answer wasn't obvious to me.)

Somebody cited one million years as the halflife of a random molecule
before volcanic activity decomposes it. Miller-Urey process might build
up lots of tarry globs over time, but lots of it would be recycled to
all the degrees of decomposition I listed earlier, so thinking of it as
a time capsule for the whole range of chemicals from stable CN to
complex single molecules might be correct?? There's an analytical
technique whereby an unidentified organic chemical is heated or somehow
shocked to partially decompose them, then the fragments are run through
a mass spectrum analyzer which can uniquely identify all the really
small fragments where isomers can't occur, then analysis of the
statistics of those fragments is used to guess the overall structure of
the molecule. Something like that partial decomposition, but of course
without the mass spectrum analysis, might have happened naturally under
the shallow primordial sea. So the flux of free-radical chemistry, the
random number generator of chemical synthesys, could have come from
both sources, build-up from CO2 and CH4 caused by UV radiation and
lightning, and break-down of tar in undersea shallow-subduction
activity. UV would make a wider variety due to the ability of UV to
break *any* bond it hits instead of only the weakest bonds, but
shallow-subduction might process a larger quantity of material per unit
time, so it's hard to say which would be more useful for generating
lots of random complex carbon-based chemicals which by chance could
become the first successful replicator.

> Well vent chemistry takes place several miles below sea level, and
> perhaps even several miles below the ocean floor.

That's true today, when the Earth's surface has miles-deep oceans
separated by miles-high continents. But on the very very smooth surface
of the early Earth, when the deepest part of the water was maybe a few
meters deep, UV exposure at the surface and convection through the
vents and other undersea volcanic activity could have been closely
coupled.

> The sun is completely irrelevant in this. These processes would still
> take place if the Earth were parked in interstellar space.

Consider the Earth's surface at a time when the Sun's radiation wasn't
yet warm enough to thaw water but geothermal activity had subsided to
allow water to condense and pool. Could it have consisted of a solid
layer of ice, fractured by tides as on Europa, overlaying a shallow
sea, overlaying the shallow-subduction&volcanism zone, overlaying the
mantle? Could an interstellar Earthlike planet have lasted like that
for a very long time, with the top layer of ice slowly vaporizing into
space, but the bottom layer being added from the sea because of the
temperature cooling, and the ocean being added from the mantle by
longterm venting of new gas?

> the Earth probably couldn't have formed in interstellar space. The
> sun is probably essential for that.

Have you been reading Sky&Telescope recently? Current theory is that in
most planetary systems, orbital resonance between small planets and
gas-giant planets throws most of the small planets inward (to be
absorbed into the star) or outward (to wander interstellar space), with
only fortunate few remaining in stable orbits as do four of our own
planetary system (five if Ceres is counted too, Luna doesn't count
since it was formed from collapse of ring around Earth formed from
debris from collision of Mars-size object, rather than formed from
collapse of planetesimals orbiting the star). By different twist of
luck, Earth might have been formed here, then tossed out to
interstellar space.

> The second is that liquid ocean water may be a necessary lubricant
> for subduction.

That's not a problem with the Europa model (fractured ice over sea over
shallow-subduction zone over mantle). Plenty of water indefinitely to
lubricate subduction. If it gets too cold at the surface, ice sublimes
slower at the top, freezes faster underneath, thicker layer of ice
traps gasses better allowing volcanic gasses to build up under the ice
and warm it again. Europa in interstellar space might actually outlast
the red-giant phase of the Sun which will melt Europa as a planet.

Any experts in planetary geology etc. care to comment on my guess that
the ice/water/shallowsubduction layering could continue for billions of
years?

.

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