Meteorites phosphates

Caro G, Bourdon B, Birck JL, Moorbath S (2003) Sm- Nd evidence from Isua metamorphosed sediments for early differentiation of the Earth s mantle. Nature 423 428-432 Chen JH, Wasserburg GJ (1981) The isotopic composition of uranium and lead in Allende inclusions and meteoritic phosphates. Earth Planet Sci Lett 52 1-15... 

Amelin, Y. (2005) Meteorite phosphates show constant 176Lu decay rate since 4557 million years ago. Science, 310, 839-841. 

Vanadium is found in about 65 different minerals among which are carnotite, roscoelite, vanadinite, and patronite, important sources of the metal. Vanadium is also found in phosphate rock and certain iron ores, and is present in some crude oils in the form of organic complexes. It is also found in small percentages in meteorites. 

Phosphorus is the eleventh element in order of abundance in crustal rocks of the earth and it occurs there to the extent of 1120 ppm (cf. H 1520 ppm, Mn 1060 ppm). All its known terrestrial minerals are orthophosphates though the reduced phosphide mineral schrieber-site (Fe,Ni)3P occurs in most iron meteorites. Some 200 crystalline phosphate minerals have been described, but by far the major amount of P occurs in a single mineral family, the apatites, and these are the only ones of industrial importance, the others being rare curiosities. Apatites (p. 523) have the idealized general formula 3Ca3(P04)2.CaX2, that is Caio(P04)6X2, and common members are fluorapatite Ca5(P04)3p, chloroapatite Ca5(P04)3Cl, and hydroxyapatite Ca5(P04)3(0H). In addition, there are vast deposits of amorphous phosphate rock, phosphorite, which approximates in composition to fluoroapatite. " These deposits are widely... 

The phosphorus chemistry occurring in interstellar matter and in the circum-stellar regions of the cosmos is not yet understood. We do, however, know that phosphorus compounds are present in meteorites, lunar rocks and Mars meteorites. Oddly enough, the element can be detected nearly everywhere, though only in low concentrations. Phosphate minerals, as well as the anions PO2 and PO3, have... 

Pasek and Lauretta (University of Arizona, Tucson) point to a further important source of phosphate they studied the corrosion of phosphide minerals from iron meteorites under various conditions in aqueous solution, e.g., using NaHCCb as a buffer, or in solutions containing MgCh and CaCL, as well as in the presence of ethanol and acetic acid. 

The synthesis of the nucleotides requires both a source of phosphate and a means of activating the phosphate group so that phosphate esters can be formed. There are three possible sources of phosphorus on the early Earth as well as from meteorites (Figure 8.9). 

Davis AM, Olsen EJ (1990) Phosphates in the El Sampal lllA iron meteorite have excess Cr and primordial lead. Lunar Planet Sci 21 258-259... 

Iron meteorites commonly contain oxygen-bearing minerals, such as chromite, phosphates, and sometimes silicates. Oxygen isotopes in such inclusions provide information on... 

Min, K., Farley, K. A., Renne, P. R. and Marti, K. (2003) Single-grain (U-Th)/He ages from phosphates in Acapulco meteorite and implications for thermal history. Earth and Planetary Science Letters, 209, 323-336. 

Nichols, R. H., Hohenberg, . M., Kehm, K., Kim, Y. and Marti, K. (1994) I-Xe studies of the Acapulco meteorite Absolute ages of individual phosphate grains and the Bjurbole standard. Geochimica et Cosmochimica Acta, 58, 2523-2561. 

The listed chemical formulae are ideal and most of these minerals contain trace and minor elements which undoubtedly affect the CL. Several of these minerals have polymorphic or compositional varieties which also may, or do, show CL (e.g. the silica polymorphs quartz, cristobalite, tridymite phosphate compositional varieties apatite, whitlockite, farringtonite, buchwaldite carbonate compositional varieties calcite, dolomite, magnesite). Glass and maskelynite (shock modified feldspar), although not strictly minerals, are relatively common. Below are described the CL observations for the most common phases including enstatite, feldspar and forsterite and they are related to their use for interpreting the mineralogy of meteorites. The observations for the other minerals are sporadic and many details have yet to be studied. 

Figure 6. Photomosaics of the cathodoluminescence of four meteorites of types 3.7-5 (a) Hedjaz (type 3.7, top right), (b) Dhajala (type 3.8, center right), (c) Bremervorde (type 4, center left), and (d) Barwell (type 5, bottom). Scale bar, as in Figure 5. These relatively high petrologic type chondrites show a uniform blue feldspar CL, with only an occasional phosphate grain with red CL.

Phosphorus is abundant on Earth, both as an element (the llth-most abundant atom in Earth s crust) and as phosphate. Meteorites hold a variety of phosphate-containing minerals and some phosphide minerals.10 Scientists at the University of Arizona have recently suggested that Fe3P, the mineral schreibersite, leads to the formation of phosphate and phosphite when corroded in water. Although phosphorylation of alcohols was not demonstrated, mechanistic considerations suggest that it should be possible. It is noteworthy that a clear prebiotic pathway for the chemical incorporation of phosphate into RNA or DNA has not been found. No nucleosides (nucleobases joined to sugars) have been reported from meteorites. Nor has evidence been found in any meteorite of the presence of nucleosides or nucleotides (nucleosides attached to phosphates). That suggests that nucleic acids were first formed as products of metabolism. 

Estimates of the abundance of zinc in the sun, in meteorites, in the Earth s core and crust, and in the oceans are very difficult to make, but its abundance in the Earth s crustal rocks and soils is of the order of 100 ppm, about 1000 times as abundant as its congeners cadmium and mercury. All three elements are Chalcophiles so that, in the reducing atmosphere that prevailed when the earth s crust solidified, they were deposited in the sulfide phase giving rise to the sulfide ores, their most important source. Eater, as weathering took place, zinc became soluble only to be precipitated as the carbonate, silicate, or phosphate. 

Davis A. M. and Olsen E. J. (1991) Phosphates in pallasite meteorites as probes of mantle processes in small planetary bodies. Nature 353, 637-640. 

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