[meteorite-list] Happy Birthday Murchison - 40th Anniversary

From: bernd.pauli at paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: 28 Sep 2009 10:37:46 UT
Message-ID: <DIIE.000000870000406F_at_paulinet.de>

Jeff wrote:

"On this day 40 years ago in 1969, one of the most famous meteorites fell to
 Earth in a spectacular fashion. It was the beautiful Murchison CM2 meteorite
 which has been the subject of much scientific interest over the last four
 decades. It's this meteorite which sparked much interest in the contained
 amino acids and the burgeoning theories of meteorites seeding life on Earth."

http://images.google.com/images?hl=en&um=1&sa=1&q=murchison+meteorite

Hi Jeff and List,

and 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
Murchison 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 raditaion 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.

See also:

Cohen B.A. et al. (1998) Racemization of meteoritic amino acids (MAPS 33-4, 1998, A033).


Best wishes from late Summer
sunny Southern Germany,

Bernd
Received on Mon 28 Sep 2009 06:37:46 AM PDT