Organic Compounds in Martian Meteorites May Be Terrestrial Contaminants

In 1996, David McKay and coworkers reported evidence suggesting the possibility of fossils in the martian meteorite ALH84001 (see PSR Discoveries article Life on Mars). This work has stimulated much discussion as to the nature and origin of organic material in ALH84001, another martian meteorite, EET79001, and other martian meteorites in general. My colleagues C. Courtney, D. A. Jeffrey, and J. W. Beck and I have been investigating the origin of the organic compounds by measuring the abundances of the isotopes of carbon (C) using accelerator mass spectrometry (AMS). Important clues to the origin of the organic material can be obtained from the amounts of 14C (frequently nicknamed radiocarbon) and the relative amounts of 13C and 12C. Our analyses indicate that at least 80% of the organic material in ALH84001 is from Earth, not Mars, casting doubt on the hypothesis the meteorite contains a record of fossil life on Mars.