>Alright. Your argument is that only strongly reducing conditions can
>produce enough amino acids to make any prebiotic scenario feasible, yet
>Miller claims that such conditions never existed. What is his evidence?
>"Considerable opinion" is not scientific evidence. If it was, there is also
>"considerable opinion" that such conditions did exist, very early, within
>the first 500 million years at least. What's more, there is even evidence
>to support that opinion.
There is substantive evidence that the earth never did have a reducing or
neutral atmosphere. The evidence has long been known, but only recently
quantified in an article in the December 1997 issue of Geology p. 1135, an
article by H. Ohmoto titled "Evidence in pre-2.2 Ga paleosols for the
early evolution of atmospheric oxygen and terrestrial biota". Ohmoto
concluded: "<i>Minimum</i> concentration of O2 in the 3.0-2.2Ga atmosphere
is calculated to be about 1.5% of the present atmospheric level [his
italics]". This conclusion delivers the final blow to those wishing the
Precambrian atmosphere to be reducing or neutral throughout most or all of
the Precambrian.
The article (abstract at
http://geosociety.org/pubs/geo9612.htm#S20)considers the behavior of soils
under anoxic and oxic conditions, concluding the oxygen levels of the
Precambrian earth were a minimum of 1.5% O2 throughout most of the
Precambrian.
Miller-Urey experiments have at least 2 orders of magnitude smaller yields
of amino acids in neutral and mildly reducing atmospheres, and do not
produce biological products at all in an oxidizing environment. This
proposal is not for a neutral or mildly reducing atmosphere. The author
emphasizes
repeatedly that his figure of 1.5% is a minimum, and likely there was more
O2 than that.