Anders: Origin of Carbonaceous Chondrites 



531 



(composition, temperature, pressure, time, energy input, catalysts, availability 

 of surfaces, etc.) has been explored. 



Some chemical evidence has become available on the Orgueil hydrocarbons 

 (Yang and Tsong, 1962). A cyclohexane extract of the meteorite shows nothing 

 but C — H groups in its infrared spectrum, indicating that it consists mainly of 

 hydrocarbons. The ultraviolet absorption spectrum shows a broad band near 

 270 m/i, but virtually no absorption above 300 m/x. Hence, aromatic ring 

 systems larger than naphthalene or biphenyl seem to be ruled out. Pre- 

 sumably, 1- and 2-ring aromatic systems with aliphatic side chains are present. 

 Chromatographic separation on silica gel resolved in the material into 5 spots, 2 

 of which fluoresced weakly under ultraviolet light. The material possessed a 

 strong, terpene-hke odor. More complex materials, including polynuclear 



1,000 



5 100 

 o 



Q. 



20 



15 



20 

 Carbon Number 



25 



Figure 10. Mass spectrum of meteorilic hydrocarbons and 2 biogenic reference materials 

 (Nagy et al., 1961). In the CnHsn.e series, the meteorilic and terrestrial mass spectra show a 

 strong resemblance to each other, but because the contribution of fragment ions to the peaks 

 is quite large in this series, the similarity in peak heights does not necessarily imply a simi- 

 larity in hydrocarbon distribution. 



hydrocarbons of higher molecular weight, bearing polar substituents, were 

 extracted from the meteorite with more polar solvents, but it seems that none 

 of these higher polynuclear hydrocarbons were present in the free state. This 

 relative simplicity of the aromatic hydrocarbon fraction was already noted by 

 Meinschein el al. (1962), on the basis of mass spectrometric analysis. 



Perhaps the hydrocarbons in Orgueil are of biogenic origin. But in our 

 opinion, the present evidence is not suthcient to justify this conclusion. 



Summary 



The carbonaceous chondrites seem to have been produced by the action of 

 liquid water on a more primitive source material. Their mineralogy implies 

 that this exposure to water occurred at temperatures near 300° K., a pH of 6-10, 

 a reduction potential of <— 0.2 volts, and that it lasted for at least 10^ years 

 (DuFresne and Anders, 1962). Their high content of chalcophile trace ele- 



