Hmmm.... I guess it would have been a good idea to state my own
views before playing the role of the skeptic so that people
don't get the wrong idea. My own preference at the moment is
for the deep sea hydrothermal vent scenario as being most
plausible. This view is very strongly influenced by several factors:
(1) potential atmosphere "problems" as being currently discussed
(2) rapid circulation of the early oceans through hydrothermal
vents (thereby destroying organics that may have been produced
a la Miller) (3) heavy meteorite bombardment subsiding about
4 billion years ago. (4) a predisposition towards nonlinear
dynamical (self-organizing) type scenarios. Intense physical
and chemical gradients in hydrothermal vents give rise to some
interesting possibilities here.
Thus, I would modify your statement "...make any prebiotic
scenario feasible" to "...make some prebiotic scenarios feasible"
Kevin:===========
>yet
>Miller claims that such conditions never existed.
No No. His claim was that it is not certain that they existed.
His view (hope) of course is that they did. But he is objective
enough to inform his readers that there is "considerable opinion"
against him. Sorry if this message got misconstrued. I thought
it relatively obvious that Miller would still be Mr. S&S
(sparks and soup). Actually, I admire Miller a great deal because
of his willingness to admit to the possible weaknesses of his
own theory and even to perform and publish experiments that
would, to some, seem to falsify his own theory. For this reason
I am very skeptical of your suggestion that Miller was being
critical of Fox out of competitiveness.
Kevin:==================
>What is his evidence?
>"Considerable opinion" is not scientific evidence.
In context, what Miller means by "considerable opinion" is
reasonable, informed, scientific opinion of experts in the
field. IOW, the results you present from Mason would also
be "opinion" in the way Miller is using the term.
I'm going to omit the Mason quote for sake of space. Let's
see what we can agree on. Can we agree that hard evidence
ends 3.8 billion years ago with the Isua rocks of Greenland?
Can we agree that at this latest point of hard evidence that
the earths atmosphere was most likely neutral or mildly
reducing? The rest seems to me to be speculation. Now, just
as there is more than one type of "opinion" there is also
more than one type of speculation. So, I'm not talking here
about wild speculations but reasonable speculations based
upon reasonable models etc.
Now, my major "complaint" here involves exaggerated optimism.
For example, your earlier "piece of cake" statement. Our
knowledge is much to rudimentary for such brash optimism,
IMHO. If one wants to say that its possible that the
earth's atmosphere prior to 3.8 billion years ago may have
been reducing and that perhaps enough organics formed in the
atmosphere or came from comets etc. to make a soup etc. etc.
then I will readily concede that its possible.
[...]
>Brian:====
>"If you check the Miller paper cited above you'll find that the yields drop
>way down for mildly reducing atmospheres. Typically less than 0.1% total
>yield, some times less than 0.001%."
>
Kevin:=======
>Funny you should mention that. In 1983 Miller co-authored a paper in the
>_Journal of Molecular Evolution_ with G Schlesinger entitled "Prebiotic
>synthesis in atmospheres containing CH4, CO, and CO2. I. Amino acids"
>[19(5):376-82]. Here is the complete abstract:
>
>"The prebiotic synthesis of organic compounds using a spark discharge on
>various simulated primitive earth atmospheres at 25 degrees C has been
>studied. Methane mixtures contained H2 + CH4 + H2O + N2 + NH3 with H2/CH4
>molar ratios from 0 to 4 and pNH3 = 0.1 torr. A similar set of experiments
>without added NH3 was performed. The yields of amino acids (1.2 to 4.7%
>based on the carbon) are approximately independent of the H2/CH4 ratio and
>whether NH3 was present, and a wide variety of amino acids are obtained.
>Mixtures of H2 + CO + H2O + N2 and H2 + CO2 + H2O + N2, with and without
>added NH3, all gave about 2% yields of amino acids at H2/CO and H2/CO2
>ratios of 2 to 4. For a H2/CO2 ratio of 0, the yield of amino acids is
>extremely low (10(-3)%). Glycine is almost the only amino acid produced from
>CO and CO2 model atmospheres. These results show that the maximum yield is
>about the same for the three carbon sources at high H2/carbon ratios, but
>that CH4 is superior at low H2/carbon ratios. In addition, CH4 gives a much
>greater variety of amino acids than either CO or CO2. If it is assumed that
>an abundance of amino acids more complex than glycine was required for the
>origin of life, then these results indicate the requirement for CH4 in the
>primitive atmosphere."
>
This sounds very much like what Miller wrote in the paper I
cited. I opted for the results at low H2/CO2 ratios because
every study I looked at said that H2 was present in trace
amounts if at all. Mason is the first author I've seen suggesting
that there may have been large amounts of H2. If there was, then
I would concede that things look much better for soup theory.
[...]
>Kevin:==
>All of which makes me wonder whether your Miller paper is really critical of
>abiogenesis, or is simply discussing the issues?
>
I'm kind of curious how anyone would think that Miller would
write a paper critical of abiogenesis :). It never occurred to
me that I would need to write a qualifier for that! :) For the
record, none of the studies I cited were critical of abiogenesis.
Some authors may be critical of a particular *theory* of abiogenesis
but it seems that all the papers I have regarding the possible
neutrality of the earth's early atmosphere take abiogenesis
to be a fact.
I really think you need to expand your horizons a little.
Abiogenesis is not a synonym for soup theory :).
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