>I did some websurfing as well:
>
>Earth's early atmosphere.
>
>
>http://seis.natsci.csulb.edu/rbehl/300i-L06.htm
>
>Evidence for the lack of free oxygen
>
> Urananite and pyrite minerals are found unoxidized in Precambrian
sediments
> Both readily oxidized today
>
> No early Precambrian iron oxides
> Fe-rich minerals in sediments deposited on land tend to rust
(oxidize)
> E.g., in alluvial fans, rivers, desert sand dunes
> Typically referred to as "red beds"
>
> Banded Iron Formations present in early Precambrian
> Mostly disappear by 1.8 - 2.5 Ga (billions of years ago)
According to Pflug(**) there are banded iron formations in the Isua rocks
of Greenland, 3.8 billion years old.
**Hans D. Pflug, "Early Geological Record and the Origin of Life,"
<Naturwissenschaften> 71:63-68, 1984.
>
> Chemical building blocks of life can't survive in the presence of O2
> Amino acids
> DNA
>
Begging the question. Reminds me of the following excercise in logic:
"Numerous experiments have shown that amino acids and a large variety
of other building blocks of living organisms can be synthesized in
electrical discharges if free oxygen is absent and if some reducing
gases are present. These experiments suggest that the earliest terrestrial
atmosphere was reducing." -- Lasaga et al, "Primordial Oil Slick,"
<Science> 174:53-55, 1971.
> The simplest living organisms have an anaerobic metabolism
> E.g., some bacteria (such as botulism), archaebacteria or archaea
which inhabit unusual
> environments
> They are killed by oxygen
>
>http://www.csuchico.edu/~jpushnik/6Abiol/abiotic.htm
>
>Formation of the Second Atmosphere
>
> Gases escaped from the molten core through volcanic activity.
> This atmosphere contained H2, H2O, CO, CO2, N2, H2S, HCN, H2CO.
> Noticeable absent is O2, making this second atmosphere a
"Reducing atmosphere"
> Water was present as vapor providing conditions for the development of
weather.
> Rains would have formed surface water deposits ("Primordial soups").
>
>
>So my view is that Art's statement that the non-reducing nature of the
early earth is well established is something that might be more wishing than
reality. I believe that there is still quite a bit of disagreement here.
>
>
>
Brian Harper
Associate Professor
Applied Mechanics
The Ohio State University
"He who establishes his arguments
by noise and command shows that
reason is weak" -- Montaigne