"A fourth problem with Miller's experiment involves Assumption No. 4,
Uniform Orientation. This assumption sates: 'Only 'left-handed' amino acids
(L-amino acids) combined to produce the proteins of life.' The amino acids
that make up the proteins of living cells are all 'left-handed' (the
L-form), but in the Miller-Urey experiments, the amino acid products found
in the apparatus are alwyas a racemic mixture, that is, 50% 'left-handed'
and 50% 'right-handed' forms." Of Pandas and Peoples, p. 50-51
Thaxton, Bradley and Olsen (The Mystery of Life's Origin, p. 139) also
mention this problem,
"The problem of using only the appropriate optical isomer has also been
ignored. A random chemical soup would have contained a 50-50 mixture of
D-and L-amino acids."
Hugh Ross also raises this issue. (Fingerprint of God p. 137)
But the data is not with the antievolutionist on this one.
In 1982 Engel and Nagy reported that the amino acids they extracted from the
Murchison meteorite were non-racemic. They found a significantly greater
percentage of L-amino acids than D-amino acids. There data is as follows:
GLU ASP PRO LEU ALA
H2O .322 .202 .342 .166 .682
H2O .30 .30 .30 nd .60
HCl .176 .126 .105 .029 .307
~Michael H. Engel and Bartholomew Nagy, "Distribution and
Enantiomeric Composition of Amino Acids in the Murchison
Meteorite", Nature , 296, April 29, 1982, p. 838.
Of course the criticism was that this represented contamination.
In 1990 Engel, Macko and Silfer repeated the experiment and obtained similar
results. A preponderance of left-handed forms.(M. H. Engel, S. A. Macko and
J. A. Silfer, "Carbon Isotope Composition of Individual Amino Acids in the
Murchison Meteorite", Nature, 348, November 1, 1990, p. 47-48.)
Once again, contamination was raised. Because of this Cronin and Pizzarello
searched to Murchison for amino acids which did not exist on earth and
tested their chirality (L- or D-). They searched for 2-a-2,3-dmpa, an amino
acid not found on earth. They write:
"Contamination of the 2-a-2,3-dmpa by a terrestrial source of the
L enantiomers seems improbable. A search of Chemical Abstracts
failed to produce a report of the natural occurrence of 2-a-2,3-
dmpa other than that in the Murchison meteorite."~John R. Cronin
and Sandra Pizzarello, "Enantiomeric Excesses in Meteoritic Amino
Acids," Science 275(February 14, 1997):951-955, p. 952
They concluded,
"The finding of enantiomeric excesses in amino acids
indigenous to the Murchison meteorite constitutes the first
natural evidence for the operation of an abiotic process for
enantiomeric enrichment. The observations suggest that organic
matter of extraterrestrial origin could have played an essential
role in the origin of terrestrial life as a provider of the
initial enantiomeric excesses from which homochirality
developed."~John R. Cronin and Sandra Pizzarello, "Enantiomeric
Excesses in Meteoritic Amino Acids," Science 275(February 14,
1997):951-955, p. 954
Now in the Sept. 18, 1997 Nature comes a report that confirms that the
original amino acids (amino acids found on earth) are indeed the product of
some process occuring in space. Due to nuclear reactions which occur in
space, which do not occur on the earth, the nuclear isotopic composition of
amino acids made in space would be different than those made on earth. In a
note to Nature Engel and Macko write:
Isotopic evidence for extraterrestrial non-racemic amino acids in the
Murchison meteorite
" Many amino acids contain an asymmetric centre, occurring as
laevorotatory, L, or dextrorotatory, D, compounds. It is
generally assumed that abiotic synthesis of amino acids on the
early Earth resulted in racemic mixtures (L- and D-enantiomers in
equal abundance). But the origin of life required, owing to
conformational constraints, the almost exclusive selection of
either L- or D-enantiomers, and the question of why living
systems on the Earth consist of L-enantiomers rather than
D-enantiomers is unresolved. A substantial fraction of the
organic compounds on the early Earth may have been derived from
comet and meteorite impacts. It has been reported previously that
amino acids in the Murchison meteorite exhibit an excess of
L-enantiomers, raising the possibility that a similar excess was
present in the initial inventory of organic compounds on the
Earth. The stable carbon isotope compositions of individual amino
acids in Murchison support an extraterrestrial origin---rather
than a terrestrial overprint of biological amino acids---although
reservations have persisted. Here the authors show that
individual amino-acid enantiomers from Murchison are enriched in
15N relative to their terrestrial counterparts, so confirming an
extraterrestrial source for an L-enantiomer excess in the Solar
System that may predate the origin of life on the Earth. "
M H Engel & S A Macko
Isotopic evidence for extraterrestrial non-racemic amino acids in the
Murchison meteorite (Letter to Nature)
Unless one believes that there is life in space, this data shows clearly
that there is an inorganic process which produces non-racemic mixtures of
amino acids. The implications for the Creation/Evolution debate are obvious.
glenn
Foundation, Fall and Flood
http://www.isource.net/~grmorton/dmd.htm