Murchison meteorite carbonaceous chondrite

Figure 4 Backscattered electron image of a highly altered Fe,Ni metal nodule in a chondrule in the Murchison CM2 carbonaceous chondrite. Thin veins of iron oxyhydroxides are present extending from the metal grain through the fine-grained rim, into the clastic matrix of the chondrite (reproduced by permission of University of Arizona and The Meteoritical Society from Meteorit. Planet. Sci, 2000, 35, 1300).

UV radiation hypothetical, but so is the transport of molecules from outer space to Earth. Recent analyses of the Murchison meteorite by two scientists from the University of Arizona, Tucson (Cronin and Pizzarello, 1997 Cronin, 1998) have shown it to contain the four stereoisomeric amino acids DL-a-methylisoleucine and DL-a-methylalloisoleucine. In both cases, the L-enantiomer is present in a clear excess (7.0 and 9.1%). Similar results were obtained for two other a-methyl amino acids, isovaline and a-methylvaline. Contamination by terrestrial proteins can be ruled out, since these amino acids are either not found in nature or are present in only very small amounts. Since the carbonaceous chondrites are thought to have been formed around 4.5 billion years ago (see Sect. 3.3.2), the amino acids referred to above must have been subject to one or more asymmetric effects prior to biogenesis. 

The Murchison meteorite shown in Figure 6.7, like all meteorites, is named after the place from which it was recovered and in this case it is the town of Murchison, Victoria in Australia about 100 km north of Melbourne. The fall occurred in 1969 and was followed by an analysis of the chemical composition in some considerable detail. The Murchison meteorite is a carbonaceous chondrite containing about 2 per cent carbon, some as inorganic carbonates, and some as soluble compounds such as amino acids but the bulk as a macromolecular heterogeneous material referred to as kerogen. 

Murchison meteorite A carbonaceous chondrite meteorite landing 100 miles north of Melbourne in a town called Murchison. 

Essentially the same amino acids, and nearly equal quantities of D and L enantiomers, were detected in the Murray meteorite, another type II carbonaceous chondrite [6]. Recent expeditions to Antarctica have returned with a large number of meteorites, many of which are carbonaceous chondrites. These may have been protected from terrestrial contamination by the pristine Antarctic ice. Careful analysis of two of these, the Yamato (74662) and the Allan Hills (77306), both type II carbonaceous chondrites, by ion exchange chromatography, gas chromatography, and GC/MS, have detected a wide variety of both protein and non-protein amino acids in approximately equal D and L abundances [9,10]. Fifteen amino acids were detected in the Yamato meteorite and twenty in the Allan Hills, the most abundant being glycine and alanine. The amino acid content of the Yamato meteorite is comparable with that of the Murchison and Murray, but the Allan Hills contains 1/5 to 1/10 that quantity. Unlike earlier meteorites from other locations, the quantities of amino acids in the exterior and interior portions of the Yamato and Allan Hills meteorites are almost identical [9,10]. Thus, these samples may have been preserved without contamination since their fall in the blue ice of Antarctica, which js 250,000 years old in the region of collection. 

Hydroxypyrimidines have been detected in the Murchison, Murray, and Orgueil carbonaceous chondrites in abundances similar to those of amino acids [7]. Earlier analyses of the Orgueil meteorite By thin layer chromatography of organic extracts indicated the presence of melamine, ammeline, adenine, and guanine [8]. Although these could not be confirmed by Folsome, et al., [7] using GC/MS, recent studies by Schwartz [11] and by Hayatsu, et al., [12] have shown that these constituents of the nucleic acids may indeed exist in the carbonaceous chondrites. 

Zitmer E (1997) Presolar material in meteorites an overview. In Astrophysical Implications of the I aboratory Study of Presolar Materials. Bematowicz TJ and Zinner E (eds) AIP, New York, p 3-26 Zinner EK, Gopel C (2002) Aluminium-26 in H4 chondrites implications for its production and its usefulness as a fine-scale chronometer for early solar system events. Meteorit Planet Sci 37 1001-1013 Zinner E, Amari S, Guitmess R, Nguyen A, Stadermann FJ, Walker RM, I wis RS (2003) Presolar spinel grains from the Murray and Murchison carbonaceous chondrites. Geochim Cosmochim Acta 67 5083-5095... 

Organic Matter in Carbonaceous Chondrites with Special Emphasis on the Murchison (CM2) Meteorite... 

The fall of a carbonaceous chondrite in September 1969 near Murchison (85 miles north of Melbourne, Australia) was an event of great importance for scientists involved in meteoritic research. In 1969, many laboratories were well equipped to analyse the lunar samples, and interest in extraterrestrial matter was at its height when suddenly 83 kg of a carbonaceous chondrite were available. The biggest fragment... 

Before leaving the aminoacids problem, it is interesting to note that aminoacids have been detected in carbonaceous chondrites found in Antarctica. The risk of contamination is much less important in Antarctica than in Australia and this is one of the reasons why these studies were undertaken. They fully confirm the results obtained on Murchison 54,55), even if in one CM carbonaceous chondrite the amino acid content was only 10% of what was observed in Murchison 56,57). The contamination is in fact lower than in Murchison the aminoacid content was very similar for samples taken near the surface of the Antarctica chondrites or from their bulk. On the other hand, all the significant analyses on Murchison were performed on samples from the interior of the meteoritic fragments due to the high degree of surface contamination. In the case of the Allende meteorite, which has the same terrestrial age as Murchison, contamination was found to extend to a depth of more than 5 mm below the surface 52). 

We do not know the extent to which the Murchison organics reflect what was available on early Earth before life emerged. The rich inventory of amino acids does not appear to be universal in carbonaceous chondrites (although the number that have been examined in detail is very small). For example, only a few amino acids (glycine, alanine, a-aminoisobutyric acid, a-amino-n-butyric acid, y-aminobutyric acid) are found in the meteorite that fell in 2000 on Tagish Lake, Canada (Table 5.3).7 The near absence of complex amino acids is significant, inasmuch as the meteorite was captured in a pristine condition soon after it fell. 

Murchison (meteorite) A carbonaceous chondrite, type II (CM2), suspected to be of cometary origin due to its high water content (12 percent)... 

Mono- and dichlorobenzenes have been found in several carbonaceous chondrites (Studier et al., 1968, 1972), but in view of the widespread human use of such compounds, it is not all certain that they are indigenous. Benzothiophenes, first reported by Hayes and Biemann (1968) in pyrolyas experiments, have also been seen in room-temperature solvent extracts (Studier et al., 1972) and hence must be original constituents of the meteorites, not thermal degradation products. Thiophene and several of its alkyl derivatives are released from Murchison at temperatures as low as 150 "C. It is not known whether these compounds can be made in FTT syntheses, because the necessary experiments have not yet been attempted. 

Hanowski N. P. and Brearley A. J. (2000) Iron-rich aureoles in the CM carbonaceous chondrites, Murray, Murchison, and Allan Hills 81002 evidence for in situ aqueous alteration. Meteorit. Planet. Sci. 35, 1291-1308. 

Sephton et al. (1998, 1999, 2000) used hydrous pyrolysis followed by supercritical extraction to examine insoluble organic matter in Orgueil (CIl), Murchison (CM2), and Cold Bokkeveld (CM2). The hydrous pyrolysates obtained for the three meteorites displayed a remarkable degree of qualitative similarity suggesting that the macro-molecular materials in different carbonaceous chondrites are apparently composed of essentially the same aromatic structural units, predominantly one to three ring alkyl-substituted aromatic structures. Significant quantitative differences were observed, however, and these were interpreted as indications of the different parent body histories of the three meteorites (Sephton et al., 2000). 

University of Texas scientists Robert Folk and F. Leo Lynch also announced the observation of fossils of terrestrial nanobacteria in another carbonaceous chondrite meteorite named the Allende meteorite. Other research has demonstrated that the Murchison and Murray meteorites... 

The Murchison carbonaceous chondite (CM2) provides the most reliable data relevant to organic materials in meteorites [31,32], because tire Murchison is one of the most famous carbonaceous chondrites and preserves many kinds of organic materials. The featiues of the organic materials are summarized as follows. 

Figure 6 The Murchison meteorite which landed at Murchison, Australia on September 28, 1969. Over / 00 kilograms of this meteorite have been collected. Classified as a carbonaceous chondrite, type II (CM2), this meteorite is likely to have come from a comet. More than 92 different amino acids have been Identified within the Murchison meteorite, nineteen of these are also found on Earth such that many believe that such meteorites provided the seeds of life on the early Earth.

PAHs found in carbonaceous chondrites show a compositional difference from the shock-synthesized PAHs in this study. The former are predominantly condensed ring compounds, whereas the latter are dominated by polyphenyl compounds. However, many PAHs reported to be present in carbonaceous chondrites could be produced by the shock reaction from benzene. Major species of PAHs in carbonaceous chondrites such as naphthalene, biphenyl, and phenanthrene were formed abundantly in this study. Furthermore, the mutual ratios of structural isomers in the Murchison meteorite [149], the Yamato-791198 meteorite [150], and the Yamato-74662 meteorite [151] resemble those of the shock products in our experiments in particular, the coincidence in the ratios of 2-MeNap/l-MeNap and fluoranthene/pyrene is striking. This implies a genetic connection between the shock products and the organic materials in carbonaceous chondrites. 

Carbonaceous chondrites, and in particular the Murchison meteorite, have a rich organic inventory, including carboxylic acids, amino acids, sulphonic acids dicarboximides and dicarboxylic acids, aliphatic and aromatic hydrocarbons and other classes of organic molecules (Table I) (for detailed reviews see 4, 19,... 

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