Carbonate in meteorite

Carr, R. H., Wright, I. P., Pillinger, C. T., Lewis, R. H. Anders, E. 1983 Interstellar carbon in meteorites Isotopic analysis using static mass spectrometry. Meteoritics 18, 277. 

Carbon has two stable isotopes, C and C. Natural diamond has 6 C-values between -3 and -5. Diamonds have been formed from carbon in the mantle with an isotopic composition that can be supposed to be in accordance with what existed for the newly created planet earth. The isotopic composition for carbon in meteorites also corresponds to a 6 C-value of -5%o. Inorganic carbonate sediments have the value 0 while organic sediments have the value -25%o. To give a total mean value of-5 the latter must constitute 20% of all sedimentary carbon. Modem estimates [4.9] assert that this value has been constant in almost 4 billion years. That implies that living organisms have been active since very early in the history of our planet... 

Latin carbo, charcoal) Carbon, an element of prehistoric discovery, is very widely distributed in nature. It is found in abundance in the sun, stars, comets, and atmospheres of most planets. Carbon in the form of microscopic diamonds is found in some meteorites. 

Despite many publications on carbynes, their existence has not been universally accepted and the literature has been characterised by conflicting claims and counter claims [e.g., 27-29]. This is particularly tme of meteoritic carbynes. An interesting account of die nature of elemental carbon in interstellar dust (including diamond, graphite and carbynes) was given by Pillinger [30]. Reitmeijer [31] has re-interpreted carbyne diffraction data and has concluded that carbynes could be stratified or mixed layer carbons with variable heteroelement content (H,0,N) rather than a pure carbon allotrope. 

The photo below, taken by the Ttl/ng spacecraft, shows that the surface of Mars has been eroded, apparently by liquid water. More recent photos transmitted by Spirit and Opportunity convince scientists that this was the case. Apparently, Mars was once much warmer than it is today. Planetary scientists speculate that at one time the atmosphere of Mars may have contained large amounts of carbon dioxide, setting up a greenhouse effect that made the surface of that planet warmer and wetter. Might there, then, have been life on Mars at some earlier time Molecular stmctures found in meteorites thought to come from Mars have been interpreted to show that there was once life there, but these results are controversial. 

Alexander von Humboldt (1769-1859) recognised meteorites as being a source of extraterrestrial material. Several well-known chemists carried out analyses of material from meteorites, starting at the beginning of the nineteenth century. Thus Louis-Jacques Thenard (1777-1857) found carbon in Alais meteorites these results were confirmed in 1834 by Jons Jacob Berzelius, who by dint of very careful work was also able to detect water of crystallisation in meteoritic material. 

The earlier assumption of a reducing atmosphere has been modified in favour of a neutral one. It is hypothetically possible that iron vapour and reduced forms of carbon from meteorite impacts on the ocean could have led to limited regions with reducing properties. 

Another recent interesting finding is that previously unknown organic polymers or "amorphous carbon," which are noble gas carriers in meteorites, are actually carbynes. Five different carbynes have been identified in the Murchison and Allende carbonaceous... 

Besides the well-known cubic form, a hexagonal form (lonsdaleite) is found in meteorites, and it is also obtained synthetically. The relation between these two forms of carbon, similar to that between the two forms (cubic and hexagonal) of ZnS (sphalerite and wurtzite) is discussed in Chapter 7. 

Carbon isotopic compositions of silicon carbide grains from the Murchison meteorite compared with the carbon isotopic compositions of carbon stars (low- to intermediate-mass AGB stars). The composition of carbon in the solar system is indicated by the vertical line. Note the similarity in the distributions of compositions in the two plots. These data indicate that the silicon carbide in the Orgueil meteorite came from a population of carbon stars very similar to that in the galaxy today. 

Gallino, R., Raiteri, . M. and Busso, M. (1993) Carbon stars and isotopic Ba anomalies in meteoritic SiC grains. Astrophysical Journal, 410, 400 411. 

Borg and Drake (2005) have determined the timing of aqueous alteration events in Martian meteorites from the ages of secondary minerals. Carbonates in ALH 84001 formed at 3.9 Ga, iddingsite in nakhlites formed -630 Myr ago, and salts in shergottites formed sometime after the crystallization of these rocks, 170 Myr ago. 

Figure 7.4 shows the reduction in sulfates and the corresponding growth of both the parent carbonates and the offspring methane with subbottom depth. The methane production is parallel but lower in isotope production than the carbonates. In Figure 7.4 the sulfur isotope (< 34S) content is defined in an identical manner to Equation 7.2 with the replacement of the fraction 13C/12C by 34S/32S in both the numerator and the denominator, using Canon Diablo meteoritic troilite as a standard. The < 34S value increases from 20-60%c before substantial biogenic methane is produced. 

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