On Wed, 05 Mar 1997 21:40:25 -0600, Glenn Morton wrote:
[...]
GM>One of the criticisms creationists make about the inorganic
>origin of life scenarios is that when amino acids are made in the
>laboratory they are 50% left handed and 50% right handed( a 50-50
>ratio is called racemic). Since a mixture of left and right handed
>amino acids make useless proteins and living forms only have left
>handed proteins, the problem has been claimed to be fatal to the
>origin of life scenario.
It still is "fatal" to every *known* naturalistic "origin of life
scenario".
GM>It has been known for a while that non-racemic amino acids
>existed in the Murchison meteorite.
Yes. Originally it was claimed that since they were racemic it
suggested the amino acids were extraterrestrial. Now they are
thought to be non-racemic, it suggests they are terrestrial:
"Added to this is the suggestive discovery of amino acids in
meteorites, including some that are important in proteins. The
Murchison meteorite, which fell in Australia in 1969, contained dl
amino acids (More recent reports challenge this interpretation. See
Michael H. Engel and Bartholomew Nagy, Nature 296, 1982, 837).
including some proteinous ones. The presence of dl-amino acids was
considered proof of extraterrestrial origin, and evidence that the
meteorite was free of contamination from earth life. This is
significant because the meteorite fell on a sheep farm, where
remaining uncontaminated would be no trifling feat!" (Thaxton C.B.,
Bradley W.L. & Olsen R.L., "The Mystery of Life's Origin:
Reassessing Current Theories, Lewis & Stanley: Dallas TX, 1992,
pp192-193)
GM>...Unless you are willing to believe in life in outer space,
>there is a mechanism (unknown to us at this moment) which is quite
>capable of producing non-racemic amino acids.
Glenn's "unknown to us at this moment" seems to indicate that he
believes that this "mechanism" will become known to us in the future.
I ask on what scientific evidence Glenn bases his belief on?
The only "mechanism" that we actually know of that is "capable of
producing non-racemic amino acids" is life itself. I personally
would not necessarily have a problem if it was proved that there was
" life in outer space". Until there is a known naturalistic way that
life can arise from non-life, as a theisti I would still consider it
needed an Intelligent Designer to get the "mechanism" started.
GM> Here is data from the Murchison meteorite in which non-racemic
>amino acids were extracted....~Michael H. Engel and Bartholomew
>Nagy, "Distribution and Enantiomeric Composition of Amino Acids in
>the Murchison Meteorite", Nature , 296, April 29, 1982, p. 838.
>
>Some of these results show that something in space was able to
>produce 70-90% L amino acids.
They don't "show" that at all. Croft points out that Engel and Nagy
didn't draw that conclusion:
"Engel and Nagy have reported during 1982 in Nature that several of
the amino acids are, in fact, only partially racemized. They
concluded that the original amino acids in the meteorite were
completely racemic but that during its descent to earth some of the
amino acids may have undergone some sort of stereoselective
decomposition." (Engel M.H. & Nagy B., Nature, 296, 1982, p837 in
Croft L.R., "How Life Began", 1988, p111)
Croft further points out that one cannot ever be certain that the
contents of a meteorite did not originate on earth:
"At best one cannot be absolutely certain that, whatever one finds in
a meteorite, it did not originate on the earth itself. Even if the
meteorite were to have been collected soon after landing and if it
had the minimum of handling, one can never be sure that it hadn't
picked up biological material from a previous encounter with the
earth. It is now known that some meteorites collide with the earth's
atmosphere and are immediately ejected back into space, only to
return many years later." (Croft L.R., 1988, p111)
Croft actually provides an alternative explanation for the amino
acids in meteorites:
"I believe there is a simple explanation for the presence of
biochemicals in meteorites. They arise from contamination by pollen
grains. Immense quantities of pollen are driven up into the upper
atmosphere by air currents. During the descent of any meteorite the
pollen grains become embedded into its surface cracks. Within the
pollen shell are an abundance of amino acids. They are all of the L-
type, but as the meteorite becomes hot, the amino acids racemize.
Finally, as it passes through layers of cloud, water droplets wash
out the amino acids from the pollen grains to leave a shell of
sporopollenin....Proof of this suggestion comes from an inspection of
the types of amino acid found in meteorites. They resemble very much
the amino acids present in honey; take for example, pipecolic acid,
a- amino butyric acid and b-alanine. These amino acids arise in
honey from pollen. In fact the amino acids found in meteorites are
characteristic of pollen. Pipecolic acid, for instance, is
characteristic of grass pollen." (Croft L.R., 1988, p111)
GM>This concept that Christians propagate that nature can't produce
>anything but racemic forms is flawed. I don't know the mechanism
>but there is one.
Until Glenn does "know the mechanism" he cannot claim that "there is
one". Apart from natural explanations given by Croft above, ie.
previous encounter or ejection from the Earth, or contamination
during descent, it is possible that God created first life elsewhere
in the Solar System or even in another solar system. It is
significant to me that Genesis 1 which deals with life on Earth only,
does not say that God created the first life on Earth. This leaves
open to me that God may have created life elsewhere and when Earth
was ready caused it to be seeded with life from outside.
GM>(See also Engel, Macko and Silfer, "Carbon Isotope Composition of
>Individual amino acids in the Murchison Meteorite," Nature 348,
>Nov. 1. 1990, pp 47-48)
I thank Glenn for his steady stream of journal references!
GM>Some people still criticised these results as being due to
>left-handed amino acid contamination. Cronin and Pizzarello
>provide strong evidence that the chirality problem (handedness) may
>not be as severe as previously thought. Peterson in an
>accompanying commentary notes,
>
>"Now chemists have furnished intriguing evidence that certain amino
>acids that formed in space 4.5 billion years ago have a small, but
>significant, excess of the left-handed form. John R. Cronin and
>Sandra Pizzarello of Arizona State University in Tempe report their
>findings in the Feb. 14 SCIENCE.
>
>"'This is the first convincing demonstration that there may be
>some natural nonbiological process that results in a slight...excess
>of the [left-handed] amino acids,' says Jeffrey L. Bada of the
>Scripps Institution of Oceanography in La Jolla, Calif.
The problem for naturalists is not just L-handed amino acids. All
sugars used in DNA are R-handed:
"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, from which a true protein could
incorporate only the L-enantiomer. Similarly, DNA uses exclusively
the optically active sugar D-deoxyribose." (Thaxton C.B., Bradley
W.L. & Olsen R.L., "The Mystery of Life's Origin", 1992, p139)
Therefore there has to be at the same time in the same place a
naturalistic means of producing R-handedness too!
>"The observations suggest that extraterrestrial, nonbiological
>organic matter could have played an essential role in the origin of
>life on Earth by providing the initial asymmetry from which a
>distinctive handedness developed, Cronin and Pizzarello contend.
See above. Even if it is shown that the L-amino acids were
extraterrestrial, it still would not show that they were the result
of a natural process unless that process is known. Science has tried
every conceivable way to make L-amino acids naturally, but has drawn
a complete blank.
the Earth was forming "4.5 billion years ago" God was preparing life
ready to seed the Earth and even other planets with. Until science
can demonstrate how life can be spontaneously generated from
non-living chemicals, it cannot be said that "This concept that
Christians propagate that nature can't produce anything but racemic
forms is flawed."
Finally, even if it is shown that there is a natural way to bias
amino acids towards left-handedness, this could be something that God
prepared and later used. There is still a long way that
naturalistists need to go to show how life spontaneously originated
from non-life.
GM>"Using sensitive analytical techniques, the researchers extracted
>and studied in meticulous detail four amino acids found in the
>carbon-rich Murchison meteorite, a type known as a carbonaceous
>chondrite. They examined amino acids that were relatively common in
>the meteorite but were not among the 20 amino acids found in
>terrestrial orangisms.
OK. But it should be remembered that this meteorite is "4.5 billion
years" old, and it may be that these "amino acids" were once
"found in terrestrial organisms" but have since become extinct.
GM>"By focussing on these particular amino acids, Cronin and
>Pizzarello could avoid problems of contamination that would bias
>the results. In each case, the researchers found an excess of the
>left-handed form of the amino acid, ranging from 2 to 9 percent.
>
>"The findings indicate that even amino acids that are never found
>in known life-forms, and so could not result from terrestrial
>biological evolution, display a left-handed bias."~I. Peterson,
>"Left-handed Excess in Meteorite Molecules", Science News, Feb 22,
>1997, p. 118
Interesting. If it was 50 or more "percent', I would find it
more convincing. In such a small sample, mayble it is just a
statistical fluke. All "known life-forms" are composed of *100%*
L-amino acids.
GM>The article itself describes their procedure "We initially
>targeted for study 2-amino-2,3- dimethylpentanoic acid
>(2-a-2,3dmpa), an amino acid with two chiral centers and,
>consequently, four steroisomers. This amino acid meets two
>important criteria: (i) It is present in the Murchison meteorite
>but has not been reported to occur in terrestrial matter, and (ii)
>its two chiral centers are resistant to epimerization because one
>9C-2) lacks a hydrogen atom and the other (C-3) has a methine
>hydrogen atom of low acidity. Consequently, it is likely that the
>chiral centers retained their original configurationsn through the
>aqueous and mild thermal processing experienced by the meteorite
>parent body and that the original enantiomer ratios have not been
>compromised by contamination."~John R. Cronin and Sandra Pizzarello,
>"Enantiomeric Excesses in Meteoritic Amino Acids," Science
>275(February 14, 1997):951-955, p. 951
>
>and
>
>"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
Which in itself is a bit of a mystery. If there was a natural
process in space that can bias amino acids acids towards
L-handedness, one why would evidnece of it only be found "in the
Murchison meteorite"? I would have thought that this suggests that
the possibility of some unusual terrestrial contamination cannot be
ruled out.
GM>"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.
I cannot see how they can draw this conclusion. It could equally be
"evidence for the operation of a" *biotic* "process" on Earth or in
space "4.5 billion years" ago.
GM>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
Even granted all the above, this may still be something that the
Intelligent Designer prepared and used. It is the planning,
preparation and putting together that is the mark of Intelligent
Design.
GM>The creationist argument, that life could not arise spontaneously
>because of the chirality problem, is beginning to look like a God of
>the Gaps argument.
Not really. Glenn is just pinning his theistic naturalistic faith in
a *Science* "of the Gaps argument". Even if "the chirality problem"
is overcome (and with only a " 2 to 9 percent" "excess of the
left-handed form of the amino acid" and in "amino acids that are
never found in known life-forms" this is far from being the case),
naturalistists still have a long way to go before they can claim that
"life could...arise spontaneously".
The fact that naturalists (including the theistic kind) have to pin their
hopes on such meagre evdience shows that they have no answers to
their origin of life questions.
God bless.
Steve
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