Re: Ways to prove or disprove


"William Morse" <wdmorse@xxxxxxxxxxxx> wrote in message news:dvo6ef$14e7$1@xxxxxxxxxxxxxxxxxxxxxx
"Perplexed in Peoria" <jimmenegay@xxxxxxxxxxxxx> wrote in
news:dv9mpt$1ac0$1@xxxxxxxxxxxxxxxxxxx:

Let me preface this - I know less about OOL than about
evolution in general. So please forgive me if my
ignorance shows.

No one knows anything about OOL. The only experts are those
who are familiar with the range of speculation and argument.

The interesting thing about the WGS equilibrium is that the
equilibrium constant for the gas-phase reaction is very close to
unity. That means that the ratio [CO]/[CO2] is about equal to the
ratio [H2]/[H2O]. I interpret this to mean that we probably will not
see much CO from WGS unless the [H2] level rises to fairly unrealistic
levels. But, it those high H2 levels do appear in vent fluids, then
we will have plenty of CO to work with and we don't need to invent
hydrogenase to make use of that reducing power.

I had suggested the WGS reaction because it is exothermic
and because I had thought that vent gases were
known to contain CO2 and H2O - but it hadn't occurred to me
that the reaction would already be at
equilibrium after passage through the vents.

Do you have a reference for the suggestion that WGS is exothermic?
I'm having trouble reconciling this with what I thought I already
knew.

However, CO, CO2, and H2 are all fairly non-polar - so they
might preferentially enter a lipid membrane. And if the CO
is rapidly removed by some anabolic reaction
(are there any that involve H2S?), then the reaction might
be driven to produce more CO.

Well, Wachtershauser suggests a formal reaction like this:

CO + H2S + FeS(solid) -> FeS2(solid pyrite) + -CHOH-(biomass)

As to whether there is a modern anabolic reaction that works as
a model of this, there is this reaction in the acetogens:

CH3OH + CO + HS-CoA -> H2O + CH3-CO-S-COA (acetyl COA)

It is also possible that CO (and HCN) were scavenged in the early
oceans by Fe++ and Ni++. These transition metal ions form complexes
with CO and CN-, but not with CO2. I believe that the biological
source of CO and HCN was the metal complexes. But in any case,
you are right that life would not run out of CO if there were
an atmosphere full of CO2 and a continuing vent resupply of H2.

As to the lipid solubilities of CO, CO2, H2S, HCN, and NH3, the
fascinating thing to me is that these molecules, when aquaeous,
will be in equilibrium with (non-lipid-soluble) conjugates
formate, bicarbonate, HS-, CN-, and NH4+.

If there is, for some reason, a pH gradient across the
membrane, this gradient can be used as an 'energy currency' to,
say, import HCN across a concentration gradient and export
NH3. And, perhaps the pH gradient can be established and maintained
by consumption of one of these chemicals on one side of the
membrane and/or production on the other side.

My guess is that life arose near vents and that CO or HCN was the
original carbon source and limiting resource. Once life figured
out how to utilize CO2 as a carbon source, the limiting resource
became the source of reducing power - probably H2S. But then
life figured out how to utilize sunlight to perform photo-assisted
oxidation of Fe++, and photons became the limiting resource.
Eventually Fe++ became rare, so life learned how to use photons
even more efficiently and oxidize water. Today, it is minor nutrients
like phosphate, potassium, and fixed nitrogen that are limiting.

Sounds plausible enough. Where do the red beds enter in? During
the photo-assisted oxidation of Fe++? Or not until oxidation of
water with an overall increase in redox potential?

I am still unclear as to the distinction between the red beds and
the BIFs. But, I am guessing that at least some Fe+++ was produced
by oxidation of Fe++ and deposited in solid form by biological
processes even before oxygenic photosynthesis was developed.

It is important to realize that the oceans may be stratified
with respect to redox potential, and that while there was a
long-term overall increase in global redox potential, locally
there may have been swings in the opposite direction. So, the
redox history of sediments is likely to be very complicated.
Nonetheless, I don't see much evolutionary reason why the
oxygenic photosynthesizers would have out-competed the Fe++
oxidizers until Fe++ became rare. Therefore, I am skeptical
of the conventional wisdom that Fe+++ is generally produced
geochemically as a result of biogenic O2. It seems to me that
if O2 can diffuse into the deep dark ocean to oxidize Fe++,
then Fe++ can diffuse into the shallow illuminated ocean and
serve as an electron source that is easier to use than water.


.

Relevant Pages

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    ... I had suggested the WGS reaction because it is exothermic and because I had thought that vent gases were ... original carbon source and limiting resource. ... During the photo-assisted oxidation of Fe++? ...
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  • Re: Ways to prove or disprove
    ... it those high H2 levels do appear in vent ... I had suggested the WGS reaction because it is exothermic ... towards H2 and CO2) at standard temperature and pressure. ... If there is, for some reason, a pH gradient across the ...
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