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No. 115: Jan-Feb 1998

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Why did life take a left turn?

Life-as-we-know-it is left-handed; that is, our amino acid molecules are levorotatory rather than the mirror-image dextrorotatory versions. Because humans "expect" symmetry in nature, it is taken for granted that everything else in the universe is split equally between leftand right-handed molecules. Earth life is just a fluke -- or is it?

On September 28, 1969, organic-rich stones fell in Victoria, Australia. This was the Murchison meteorite, and it may carry a message. Over a decade ago, M.H. Engel and B. Nagy reported that the organic molecules in the Murchison meteorite were not split 50:50 between left- and right-handed versions. So contrary to expectations was this finding that most scientists assumed that the analysis was contaminated by terrestrial organic molecules. Now, M.H. Engel and S.A. Macko have refined the analytical techniques and apparently avoided any taint of contamination. Their conclusion: the Murchison amino acids still lean to the left.

From all this arise several intriguing possibilities:

  1. Life on earth started split evenly between left- and right-handed amino acids, but was nudged to the left by the influx of organic-laden meteorites like the Murchison.
  2. Terrestrial life actually originated elsewhere in the universe where much matter is left-handed, including life, if it exists there. In other words, our philosophical expectation of symmetry in the universe-as-a-whole is incorrect.
  3. The universe on the average is evenly split between left- and right-handed molecules, but there are "islands" or "pockets" which are left- or right-handed. Earth life is one of these "islands."
  4. Given the chance, amino acids and other organic molecules would exist evenly split, but physical phenomena, such as circularly polarized light, tip the scales -- to the left, in the case of terrestrial life. But that would mean that some physical phenomena are not symmetrical!

(Engel, M.H., and Macko, S.A.; "Isotopic Evidence for Extraterrestrial Nonracemic Amino Acids in the Murchison Meteorite," Nature, 389:265, 1997. Also: Chyba, Christopher F.; "A Left-Handed Solar System," Nature, 389:234, 1997.)

Comment. The references above state that terrestrial life is almost exclusively left-handed. Are there really righthanded organic molecules in terrestrial life forms? Where?

Left- and right-handed versions of the amino acid alanine Left- and right-handed versions of the amino acid alanine.

From Science Frontiers #115, JAN-FEB 1998. 1998-2000 William R. Corliss

Science Frontiers Sourcebook Project Reviewed in:


  • "A sourcebook of unexplained phenomena is therefore a valuable addition to a collection of scientific literature. William R. Corliss has provided this in the past with his source books of scientific anomalies in several subjects, and now he has provided it for astronomy. He has done an excellent job of collecting and editing a large amount of material, taken in part from scientific journals and in part from scientific reporting in the popular or semi-scientific press." -- "The Mysterious Universe: A Handbook of Astronomical Anomalies", reviwed by Thomas Gold, Cornell University, in Icarus, vol.41, 1980

  • "An interesting, systematic presentation of unusual weather [..] This book is recommended for a general audience" --"Corliss, William R., Tornados, Dark Days, Anomalous Precipitation, and Related Weather Phenomena, Sourcebook Project, 1983.", revieweed in Choice, September 1983
  • "..the science is necessarily somewhat speculative, but Corliss's symthesis is based on reputable sources." -- "Corliss, William R. (Compiler). Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena" reviwed by Joseph M. Moran, Univ. of Wisconsin in Science Books and Films, Sep/Oct 1983

  • "Before opening the book, I set certain standards that a volume which treads into dangerous grounds grounds like this must meet. The author scrupulously met, or even exceeded those standards. Each phenomenon is exhaustively documented, with references to scientific journals [..] and extensive quotations" -- "Book Review: The moon and planets: a catalog of astronomical anomalies", The Sourcebook Project, 1985., Corliss, W. R., Journal of the Royal Astronomical Society of Canada, Vol. 81, no. 1 (1987), p. 24., 02/1987