Carbonaceous meteorite

Fig. 2.7 The distribution of the ratio of the two hydrogen isotopes (D/H) in carbonaceous meteorites compared with that on Earth and in the comets. According to this distribution, most of the water on Earth must have had its origin in meteorites. From Robert (2001)...

Carbonaceous meteorites. Geochim Cosmochim Acta 36 377-394 Black DC, Pepin RO (1969) Trapped neon in meteorites. II. Earth Planet Sci Lett 6 395-405 Bogdanovski O, Papanastassiou DA, Wasserburg GJ (2002) Cr isotopes in Allende Ca-Al-rich inclusions. Lunar Planet Sci XXXIII 1802... 

Clayton RN, Grossman L, Mayeda TK (1973) A component of primitive nuclear composition in carbonaceous meteorites. Science 182 485-488... 

Robert F, Epstein S (1982) The concentration and isotopic composition of hydrogen, carbon and nitrogen carbonaceous meteorites. Geochim Cosmochim Acta 46 81-95 Robert F, Merlivat L, Javoy M (1978) Water and deuterium content in ordinary chondrites. Mete-oritics 12 349-354... 

Lawless, J. G. and Yuen, G. U. (1979). Quantification of monocarboxylic acids in the Murchison carbonaceous meteorite. Nature, 282, 396-8. 

Yuen, G. U. and Knenvolden, K. A. (1973). Monocarboxylic acids in Murray and Murchison carbonaceous meteorites. Nature, 246, 301-2. 

Scholer HF, Nkusi G, Niedan VW, Muller G, Spitthoff B (2005) Screening of Organic Halogens and Identification of Chlorinated Benzoic Acids in Carbonaceous Meteorites. Chemosphere 60 1505... 

Bematowicz, T., Fraundorf, G., Tang, M., Anders, E., Wopenka, B., Zinner, E. Fraundorf, P. 1987 Evidence for interstellar SiC in the Murray carbonaceous meteorite. Nature, Lond. 330, 728 730. 

Nagy, B. Carbonaceous Meteorites, Elsevier Scientific Publishing Co., Amsterdam 1975... 

Lange, M. A., Lambert, E, Ahrens, T. I. (1985) Shock effects on hydrous minerals and implications for carbonaceous meteorites. Geochim. Cosmochim. Acta, 49, 1715-26. 

Although it is clear that complex lipids can be synthesized under laboratory simulations using pure reagents, the list of required ingredients does not seem plausible under prebiotic conditions. Therefore, it is unlikely that early membranes were composed of complex lipids such as phospholipids and cholesterol. Instead, there must have been a source of simpler amphiphilic molecules capable of self-assembly into membranes. One possibility is lipidlike fatty acids and fatty alcohols, which are products of FTT simulations of prebiotic geochemistry [12] and are also present in carbonaceous meteorites. Furthermore, as will be discussed later, these compounds form reasonably stable lipid bilayer membranes by self-assembly from mixtures (Fig. 4a). 

Is this a plausible premise In order to approach this question, we can assume that the mixture of organic compounds in carbonaceous meteorites such as the Murchison meteorite resembles components available on the early Earth through extraterrestrial infall. A series of organic acids represents the most abundant water-soluble fraction in carbonaceous meteorites [ 15,67,68]. Samples of the Murchison meteorite were extracted in an organic solvent commonly used to extract membrane lipids from biological sources [69,70]. When this material was allowed to interact with aqueous phases, one class of compounds with acidic properties was clearly capable of forming membrane-bounded vesicles (Fig. 7). 

Fig. 7 Membranes can be formed by components of carbonaceous meteorites [69,70]. a The Murchison meteorite contains approximately 2% organic carbon by weight, b Organic compounds can be extracted from the meteorite by a lipid solvent system (chloroform-methanol), then separated by two-dimensional chromatography. Polycyclic compounds in the mixture produce fluorescent spots, c The organic acid fraction from the TLC plate readily assembles into membranous vesicles when exposed to dilute aqueous solutions buffered at pH 8-9. The vesicles were photographed by their autofluorescence. Scale bar shows 20 im...

Exobiological research offers reasons to expect that amino acids might be universal. Amino acids appear to be products of prebiotic synthesis. They are famously the products of the Miller process by which methane, ammonia, and water were subjected to electrical discharge. And amino acids are found in carbonaceous meteorites both as alpha amino acids that are standard in terran life and as the nonstandard alpha-methylamino acids found by Cronin and Pizzarello.24... 

Cooper, G., Novelle, K., Belisle, W., Sarinana, J., Brabham, K., and Garrel, L. 2001. Carbonaceous meteorites as a source of sugar-related organic compounds for the early Earth. Nature 414 879-884. 

Pizzarello S. The chemistry of life s origin a carbonaceous meteorite perspective. Acc. Chem. Res. 2006 39 231-237. 

Black D. C. (1972) On the origins of trapped helium, neon, and argon isotopic variations in meteorites II. Carbonaceous meteorites. Geochim. Cosmochim. Acta 36, 377-394. 

Kerridge J. F. (1964) Low-temperature minerals from the finegrained matrix of some carbonaceous meteorites. Ann. NY Acad. Set 119, 41-53. 

Nagy B. (1966) Investigation of the Orgueil carbonaceous meteorite. Geol. Foren. Stockholm Forh. 88, 235-272. 

The most ancient organic molecules available for study in the laboratory are those carried to Earth by infalling carbonaceous chondrite meteorites. All the classes of compounds normally considered to be of biological origin are represented in carbonaceous meteorites and, aside from some terrestrial contamination it is safe to assume that these organic species were produced by nonbiolo-gical methods of synthesis. In effect, carbonaceous chondrites are a namral laboratory containing... 

---