Murchison chondrite

The question as to the potential availability of the requisite amphiphilic precursors in the prebiotic environment has been addressed experimentally by Deamer and coworkers, [143,145] who looked into the uncontaminated Murchison chondrite for the presence of such amphiphilic constituents. Samples of the meteorite were extracted with chloroform-methanol and the extracts were fractionated by thin-layer chromatography, with the finding that some of the fractions afforded components that formed monomolecular films at air-water interfaces, and that were also able to self-assemble into membranous vesicles able to encapsulate polar solutes. These observations dearly demonstrated that amphiphiles plausibly available on the primitive Earth by meteoritic infall have the ability to self-assemble into the membranous vesides of minimum protocells. ... 

Hiyagon H. and Hashimoto A. (1999a) excesses in olivine inclusions in Yamato-86009 and Murchison chondrites and their relation to CAIs. Science 283, 828-831. 

Twenty-two amino acids were detected by early analyses of the Murchison chondrite, 8 of which were biologically common, 10 of which liad a restricted occurrence on the Earth, and 4 of which had no natural terrestrial source [33]. Further analyses identified 75 amino acids in the Miuchison [34] 8 of them were biologically common, 11 of them were uncommon, and 55 of them had no terrestrial source [35-37]. 

Even more convincing than the spectroscopic proof of amino acids in the imiverse is the chemical analysis of chondrites (meteorites). Seventeen amino acids were discovered in the Murchison chondrite, which was found in Australia ten of these do not occur in Nature (on Earth). In terms of the total amino acid content of the Murchison chondrite, about one third consists of glycine. 

From the Murchison chondrite meteorite, the [Lu/Hf] ratio was taken as 0.24 and, assuming that the age of the chondritic reservoir is 4.55 Ga, the present value of the... 

The authors chose pyruvic acid as their model compound this C3 molecule plays a central role in the metabolism of living cells. It was recently synthesized for the first time under hydrothermal conditions (Cody et al., 2000). Hazen and Deamer carried out their experiments at pressures and temperatures similar to those in hydrothermal systems (but not chosen to simulate such systems). The non-enzymatic reactions, which took place in relatively concentrated aqueous solutions, were intended to identify the subsequent self-selection and self-organisation potential of prebiotic molecular species. A considerable series of complex organic molecules was tentatively identified, such as methoxy- or methyl-substituted methyl benzoates or 2, 3, 4-trimethyl-2-cyclopenten-l-one, to name only a few. In particular, polymerisation products of pyruvic acid, and products of consecutive reactions such as decarboxylation and cycloaddition, were observed the expected tar fraction was not found, but water-soluble components were found as well as a chloroform-soluble fraction. The latter showed similarities to chloroform-soluble compounds from the Murchison carbonaceous chondrite (Hazen and Deamer, 2007). 

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. 

Figure 6.9 Laser desorption mass spectra of extracts of the Murchison and Allende carbonaceous chondrites and an extraction from the K/T boundary. (Adapted from Becker L, Poreda R. J. and Bunch T. E., 2000 by permission of the Proceedings of the National Academy of Sciences 97 2979)...

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. 

Several factors indicate that the amino acids detected in all of these carbonaceous chondrites are indigenous and that they must have originated abiotically. First, the presence of protein and non-protein amino acids, with approximately equal quantities of D and L enantiomers points to a nonbiological origin and precludes terrestrial contamination. In addition, the non-extractable fraction of the Murchison is significantly heavier in 13C than terrestrial samples. Finally, the relative abundances of some compounds detected resemble those of products formed in prebiotic synthesis experiments. The aliphatic hydrocarbons are randomly distributed in chain length, and the C2, C3, and C4 amino acids have the highest concentrations (i.e., the most easily synthesized amino acids with the least number of possible structures are most abundant) [4]. 

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. 

Hinton RW, Davis AM, Scatena-Wachel DE (1987) Large negative Ti anomalies in refractory inclusions from the Murchison carbonaceous chondrite evidence for incomplete mixing of neutron-rich supernova ejecta into the solar system. Astrophys J 313 420-428... 

Hoppe P, Amari S, Zinner E, Ireland T, Lewis RS (1994) Carbon, nitrogen, magnesium, silicon and titanium isotopic compositions of single interstellar silicon carbide grains from the Murchison carbonaceous chondrite. Astrophys J 430 870-890... 

Hutcheon ID, Steele IM, Wachel DES, MacDougall JD, Phinney D (1983) Extreme Mg fractionation and evidence of Ti isotopic variations in Murchison refractory inclusions. Lunar Planet Sci XIV 339-340 Hutcheon ID, Hutchison R (1989) Evidence from the Semarkona ordinary chondrite for A1 heating of small planets. Nature 337 238-241... 

MacPherson GJ, Bar-Matthews M, Tanaka T, Olsen E, Grossman L (1983) Refractory inclusions in the Murchison meteorite. Geochim Cosmochim Acta 47 823-839 MacPherson GJ, Wark DA, Armstrong JT (1988) Primitive material surviving in chondrites refractory inclusions. In Meteorites and the Early Solar System. Kerridge JF, Matthews MS (eds) University of Arizona Press, Tucson, p 746-807... 

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... 

Kerridge JF, Chang S, Shipp R (1987) Isotopic characterization of kerogen-hke material in the Murchison carbonaceous chondrite. Geochim Cosmochim Acta 51 2527-2540 Kharaka YK, Berry FAF, Friedman I (1974) Isotopic composition of oil-field brines from Kettle-man North Dome, California and their geologic implications, Geochim Cosmochim Acta 37 1899-1908... 

Deamer, D. W. (1985). Boundary structures are formed by organic components of the Murchison carbonaceous chondrite. Nature, 317, 792. ... 

The degree of equilibrium isotopic fractionation among phases depends on temperature, so the isotopic compositions of co-existing phases can be used for thermometry. Oxygen is widely used in this way. For example, Clayton and Mayeda (1984) found that the oxygen isotopic compositions of calcite and phyllosilicates from Murchison lie on a mass-dependent fractionation line and differ in 6180 by 22%o. This difference requires a temperature of around 0 °C, which is interpreted to be the temperature of aqueous alteration on the Murchison parent asteroid. Similar measurements for Cl chondrites indicate that aqueous alteration for these meteorites occurred at higher temperature, 50-150 °C (Clayton and Mayeda, 1999). 

Clayton, R. N. and Mayeda, T. K. (1984) The oxygen isotope record in Murchison and other carbonaceous chondrites. Earth and Planetary Science Letters, 67, 151-166. 

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