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 ______________________________________________ http://www.meteoritecentral.com Meteorite-list mailing list [email protected] http://six.pairlist.net/mailman/listinfo/meteorite-list
