Amino acid analyses using HPLC of pristine interior pieces of the CI carbonaceous chondrites Orgueil and Ivuna have found that ␤-alanine, glycine, and ␥-amino-n-butyric acid (ABA) are the most abundant amino acids in these two meteorites, with concentrations ranging from Ϸ600 to 2,000 parts per billion (ppb). Other ␣-amino acids such as alanine, ␣-ABA, ␣-aminoisobutyric acid (AIB), and isovaline are present only in trace amounts (<200 ppb). Carbon isotopic measurements of ␤-alanine and glycine and the presence of racemic (D͞L Ϸ 1) alanine and ␤-ABA in Orgueil suggest that these amino acids are extraterrestrial in origin. In comparison to the CM carbonaceous chondrites Murchison and Murray, the amino acid composition of the CIs is strikingly distinct, suggesting that these meteorites came from a different type of parent body, possibly an extinct comet, than did the CM carbonaceous chondrites. 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, Ivu...

Abstract-Amino acid analyses of the Antarctic CM2 chondrites Allan Hills (ALH) 83100 and Lewis Cliff (LEW) 90500 using liquid chromatography-time of flight-mass spectrometry (LC-ToF-MS) coupled with UV fluorescence detection revealed that these carbonaceous meteorites contain a suite of indigenous amino acids not present in Antarctic ice. Several amino acids were detected in ALH 83100, including glycine, alanine, β-alanine, γ-amino-n-butyric acid (γ-ABA), and α-aminoisobutyric acid (AIB) with concentrations ranging from 250 to 340 parts per billion (ppb). In contrast to ALH 83100, the CM2 meteorites LEW 90500 and Murchison had a much higher total abundance of these amino acids (440-3200 ppb). In addition, ALH 83100 was found to have lower abundances of the α-dialkyl amino acids AIB and isovaline than LEW 90500 and Murchison. There are three possible explanations for the depleted amino acid content in ALH 83100: 1) amino acid leaching from ALH 83100 during exposure to Antarctic ice meltwater, 2) a higher degree of aqueous alteration on the ALH 83100 parent body, or 3) ALH 83100 originated on a chemically distinct parent body from the other two CM2 meteorites. The high relative abundance of ε-amino-n-caproic acid (EACA) in the ALH 83100 meteorite as well as the Antarctic ice indicates that Nylon-6 contamination from the Antarctic sample storage bags may have occurred during collection.

The extent of racemization of aspartic acid, alanine, and leucine provides criteria for assessing whether ancient tissue samples contain endogenous DNA. In samples in which the D/L ratio of aspartic acid exceeds 0.08, ancient DNA sequences could not be retrieved. Paleontological finds from which DNA sequences purportedly millions of years old have been reported show extensive racemization, and the amino acids present are mainly contaminates. An exception is the amino acids in some insects preserved in amber.