Re: Snowball Earth at 2.3 gya

We really don't know if the impact 4.5bya lost all of the original
atmosphere. A "secondary atmosphere" puts the cart before the horse,
in my perspective. An oxygenating atmosphere requires free oxygen,
doesn't it? Oxygen was chemically locked-up in the high temperature
environment of the early earth. Logic doesn't allow CO2 as the primary
greenhouse gas. Volcanic CO2 comes from limestone breakdown in
tectonic plate subduction. Free nitrogen in volcanic eruption is from
oceanic bed nitrate breakdown and plate subduction.
I would agree that the anaerobic photosynthesis (that I mentioned)
occuring in estuaries would have occured first. This is likely the
pathway modified to the oxygen-producing photosynthesis, which would
produce this gas close to the surface. The kind of "Winogradsky
column" organization you mentioned fits this pattern.


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