528 



Annals New York Academy of Sciences 



Unfortunately, Boato measured only the total combustible carbon, and not 

 the fractionation among the several forms of carbon in the meteorite. There 

 seems to be a correlation between decreasing C'^ content and decreasing total 

 carbon in the meteorite. Boato suggested that this imphed preferential loss 

 of C" during partial volatilization, and pointed out that a similar depletion 

 had been observed in terrestrial processes that were accompanied by a loss of 

 volatiles, e.g., the conversion of dead organisms to petroleum. For the purpose 

 of the present discussion, it is immaterial whether this last process is abiotic or 

 biotic; any low-temperature process will lead to qualitatively similar fractiona- 

 tions. 



Urey (1962) suggested that sulfur metabolizing organisms might be responsi- 

 ble for the oxidized sulfur compounds (S and MgS04) in the carbonaceous 

 chondrites. However, as seen in table 7, the elemental sulfur in Orgueil is 

 enriched in S^^ relative to the sulfate (Thode and DuFresne, 1961), whereas 

 sulfur bacteria as well as inorganic processes occurring under equilibrium condi- 



Table 7 

 Sulfur Isotopic Composition in Carbonaceous Chondrites 



* DuFresne & Thode (1961). 



t Thode, Wanless & VVallouch (1954). 



tions tend to produce just the opposite fractionation, depleting elemental S in 

 S''^ (Thode et al., 1954). The equilibrium constant for the reaction 



s^-'Or + H Ss^^ ^ S3404= + H Ss'^ 



is 1.071 at 25° C. (Tudge and Thode, 1950), so that the sulfur and sulfate in 

 Orgueil are clearly out of equilibrium. Perhaps the origin of the higher oxida- 

 tion states of sulfur will be clarified by further isotope measurements on the 

 troilite in Orgueil (Thode and Anders, 1962). 



Boato (1954) also measured the hydrogen isotopic composition of the hy- 

 drated silicates in carbonaceous chondrites. His results (table 8) show that 

 the D/H ratio in Ivuna, Orgueil, and Mokoia was considerably higher than that 

 in terrestrial waters. This fractionation may have been caused by kinetic 

 isotope effects during formation of the hydrated silicates (Clayton, 1961) or 

 by extensive evaporation of the water in the meteorite parent body. 



Hydrocarhous. Finally, a few words should be said about the hydrocarbons 

 (Nagy el al., 1961). This matter has been discussed in greater detail elsewhere 

 (Meinschein, 1961; Anders, 1961, 1962a; Nagy el al., 1962a; Meinschein et al, 

 1962). For the present discussion, only three of the most salient points will be 

 restated. 



Meinschein and his associates certainly deserve great credit for determining 



