[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: Murchison

>For some detailed information on amino acids found in Murchison
>(specifically the enatiomeric excess), check "Science" February 14, 1997
>issue. 

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 
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.

Ron Baalke