Home Page Science Frontiers

No. 111: May-Jun 1997

Issue Contents

Other pages











Extraterrestrial Handedness

Human life forms favor right-handedness over left-handedness by a 9:1 ratio. Other terrestrial animals are also asymmetrical in various ways. But on the molecular level, terrestrial biochemistry is all left-handed. As far as scientists can determine, only left-handed amino acids are incorporated into proteins. In nonlife (if such a state really exists), amino-acid molecules are right- and lefthanded in equal numbers -- as least this has been the theory up until now.

Amino acids are found in substances we assume are non-life or of abiotic origin. In fact, amino acids are present in meteorites, often in substantial amounts. They are profuse in Australia's Murchison meteorite, a carbonaceous chondrite. However, analysis of the Murchison's amino acids indicates that there are slightly more (7-9%) left-handed than right-handed amino acids present.

This extraterrestrial handedness is of great import to both cosmologists and biologists, because the carbonaceous chondrites are thought to have formed 4.5 billion years ago -- long before life on earth originated. Furthermore, some of the Murchison's amino acids have never been found in terrestrial life, and they are also slightly left-handed. For some unfathomed reason, chemical and biological evolution both tilt to the left!

(Bada, Jeffrey L.; "Extraterrestrial Handedness?" Science, 275:942, 1997. Cronin, John R., and Pizzarello, Sandra; "Enantiomeric Excesses in Meteoritic Amino Acids," Science, 275:951, 1997. Also: Peterson, I.; "Left-Handed Excess in Meteorite Molecules," Science News, 151:118, 1997. Note that left-handed amino acids in the Murchison meteorite were also reported in the early 1980s: Kerr, Richard A.; "Odd Amino Acids in a Meteorite," Science, 216:972, 1982.)

Comments. This discovery of a tilted universe means that we cannot confirm Martian life with spacecraft instruments that test for an excess of left-handed amino acids.

Human philosophers, from the ancient Greeks to the present, like to think the universe is in balance, that equality reigns, yin and yang, and similar presumptions. But, let's face it: our particular universe is lopsided. Of course, our universe may be balanced by another one far away, where everything, including its intelligent life forms, are made from right-handed amino acids -- chemically speaking, a mirror image of our universe. Balance could thus be preserved at that scale.

From Science Frontiers #111, MAY-JUN 1997. 1997-2000 William R. Corliss