Carbonaceous chondrites provide some of the most primitive solar system material available for study and are known to contain a wide variety of organic compounds (1). In particular, one group of carbonaceous chondrites, the CIs, which have been altered extensively by water on their parent body, have been found to contain high abundances of organic carbon. Orgueil, the most well known CI carbonaceous chondrite, fell in France on May 14, 1864 at a time when organic and analytical chemistry were in their infancy. Nevertheless, by using techniques available at the time, chemists soon showed that the meteorite contained organic material probably of extraterrestrial origin (2). Some scientists even speculated that the Orgueil organic material was produced by extraterrestrial organisms and thus provided evidence for panspermia, a process wherein life on Earth was seeded by a bacterial spore from another world that had hitchhiked on a meteorite that had fallen to Earth (3). Pasteur briefly examined the Orgueil meteorite and found no evidence for bacteria, a finding that he evidently considered so unimportant that it was never published except in his notebooks (4).
The possibility that Orgueil contained evidence for extraterrestrial life resurfaced in the 1960s when Nagy and coworkers published a series of papers claiming that the meteorite contained biogenic hydrocarbons along with "organized elements" that supposedly resembled fossilized algae (5, 6). These claims generated an intense debate, and soon it was shown that the hydrocarbons were terrestrial contaminants and the organized elements were ragweed pollen (7, 8).
Because of these controversies, the CI meteorite Orgueil has seldom been studied by using the modern analytical techniques now available to investigate organic compounds in meteorites. The last amino acid analysis of Orgueil was reported in 1972 when GC analysis using a chiral derivatizing reagent showed that the meteorite contained D- and L-amino acids and other amino acids such as -alanine, -aminoisobutyric acid (AIB), and -AIB, which generally are not present in terrestrial living organisms (9). Surprisingly, Ivuna, another CI carbonaceous meteorite that fell in Tanzania on December 16, 1938, has rarely been investigated for organic components, perhaps because of the controversies over Orgueil. Thus far in the only study to date, Ivuna has been found to contain a distribution of polycyclic aromatic hydrocarbons that is unique among other carbonaceous chondrites (10).
In contrast to the CIs, the CM-type chondrites Murchison and Murray, which fell in Australia in 1969 and in Kentucky in 1950, respectively, have been analyzed extensively for organic compounds by using modern techniques. Over 70 different amino acids have been detected in Murchison, the majority of which have no known terrestrial occurrence (1). The Murchison amino acids also have been shown to have unusual carbon, nitrogen, and hydrogen isotopic signatures that provide additional evidence of their extraterrestrial origin (11-13).
To enhance our knowledge of CI carbonaceous chondrites, we report here the results of amino acid analyses of Orgueil and Ivuna by using highly sensitive analytical techniques recently developed to study meteorites (14, 15).