wrote in message
news:c8098r$236r$1{at}darwin.ediacara.org...
> > From: jimmenegay{at}sbcglobal.net (Jim Menegay)
> > My speculation (that early major Fe+++ deposits were directly biogenic,
> > rather than indirect via biogenic O2) is based on two observations:
> > 1.  The biochemistry of oxidizing H2O to O2 is very complex.  The
> > biochemistry of oxidizing Fe++ to Fe+++ is much simpler, and seems
> > to be integral to all electron transport chains.  While Fe++ was widely
> > available, there seems to be little incentive for life to develop the
> > complex machinery for oxidizing H2O.
>
> Are you suggesting that when there was plenty of Fe++ dissolved in the
> ocean, life used the simpler biochemistry to directly convert it to
> Fe+++, which slowly precipated out of the ocean? But until it was
> seriously depleted, there was enough of it to go around, so some other
> resource was consumed to the limit, leaving none of it availble as
> surplus for other forms of life that didn't need Fe++ to use. But when
> enough of the Fe++ was gone and volcanic activity had reduced to the
> point where it wasn't being re-supplied enough, Fe++ became the
> limiting nutrient in the ocean, which caused all life dependent on
> consuming it to decline in abundance, leaving some of other nutrients
> available for other forms of life to grow on?
>
> Some of these other forms of life first chanced upon a way to convert
> sunlight into useful energy, using H2S and other sulfur compounds as
> the hydrogen donor, which led the way to eventual discovery of a
> variant of that method to use H2O as the hydrogen donor, which suddenly
> filled the atmosphere with O2 and filled the ocean with dissolved O2
> which suddenly eliminated the already low level of Fe++ in the ocean,
> changing the previous longterm slow problem into a sudden crisis?

That's my story and I'm sticking to it!

But I should point out that "sudden" in this context means "over a
period of 100 million years or so".
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