[meteorite-list] Murchison

From: Bernd Pauli HD <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 10:06:56 2004
Message-ID: <3DA07041.5886963E_at_lehrer.uni-karlsruhe.de>

Charles O'Dale wrote:

> Bernd: I found the Murchison article fascinating! Thank you.

My pleasure!

> regarding the left/right distribution of organic molecules
> in the meteorite, is there a theory on why life on earth
> contains predominantly left handed molecules?


Hello Chuck and List,

On Friday, 12 Sep 1997, Ron Baalke posted this:


Amino acids have been found in Murchison and other carbonaceous
meteorites. There are two types of amino acids, one group which is
characterized as being "left-handed" and the other group "right-handed".
Amino acids can be formed from biological and non-biological means.
However, it is interesting to note that all life known thus far produce
the left-handed amino acids. No one really knows why life has a
preference for left-handed amino acids. Murchison has been observed to
have an excess of left-handed amino acids. Is this an indication of life
in the Murchision meteorite? Under normal circumstances, you would
expect an equal number of left-handed and right-handed amino acids to
form if they were formed from non-biological means. Some people
speculated that this is a sign of life in Murchison. However, the excess
of left-handed amino acids alone is not an indication of life, as such
an excess can be explained by non-bioligical means. The excess of
left-handed amino acids in Murchison is rather small, with the excess
ranging from 2.8% to 10.4%. In a paper titled "Distinguishing the
Chiral* Signature of Life in the Solar System and Beyond" given by
Alexandra MacDermott at the SPIE conference in July 1997, she explains
how amino acids could be formed from non-biological means and show an
excess of either left-hand or right-handed amino acids. It has been
clearly shown in the laboratory that circular polarized light exposure
can be used to force the selection of which hand amino acids will be.
MacDermott proposes that early in the formation of the the solar system,
it was exposed to circularly polarized radiation of a passing neutron
star. Which pole of the neutron star facing the solar system would
determine which hand the pre-solar dust cloud would have an excess of.
MacDermott concluded that the excess of left-handed amino acids in
Murchison was not due to biological means, and an excess of amino acids
on its own does not necessarily imply life. MacDermott also remarked
that if Richard Hoover's paper on finding possible microfossils in
Murchison (which was also presented the day before at the same SPIE
conference) bears out to be true, then she would have to rethink the
conclusions from her paper.

* chiral / chirality = (of a molecule) not superimposable on its mirror
image.
Received on Sun 06 Oct 2002 01:17:53 PM PDT