Anders: Origin of Carbonaceous Chondrites 



529 



the mass spectrum of the hydrocarbons in the meteorite, and for drawing atten- 

 tion to its possible resemblance to the mass spectra of biogenic hydrocarbons. 

 One point on which we disagree, however, is the extent of such resemblance. 

 FIGURES 9 and 10, plotted from their data, show the worst and the best cases, 

 respectively. If the comparison is extended to the entire mass spectrum, and 

 to a larger variety of biogenic reference materials, certain additional resem- 

 blances, but also certain differences appear. It seems very difficult to decide, 

 on purely objective grounds, whether these resemblances are strong enough to 

 prove a biological origin. 



There is also a question to what extent the peak height at a given mass num- 

 ber may be taken as a measure of the amount of parent hydrocarbon of this 

 mass. This is a good assumption for the [CnHiH+o]"^ ions derived from the 

 CnH.2n+2 paraffius. But as one goes to compounds progressively poorer in 

 hydrogen, the ambiguity increases. The [CnH-in-e]"*" ions are derived not only 

 from the C„H-2„_6 ( = tetracycloalkane) series, but also from the CuH2u+2 , 



Table 8 

 Hydrogen Isotopic Composition in Carbonaceous Chondrites (Boato, 1954) 



CnHon , CnH2n-2 , aud CnH2n-4 families, with possible additional contributions 

 from nitrogen and oxygen compounds. Thus, it seems fair to attribute most 

 ob the observed peak height in the C„H2n+2 series to paraffins. However, just 

 in the case of this series, the resemblance is rather poor (figure 9), and the 

 great difference between the spectra of the original Orgueil distillate (Nagy 

 et al., 1961) and the chromatographically separated hydrocarbon fraction 

 (Meinschein, 1961) shows that even in this favorable case, some 70 to 90 per 

 cent of the originally observed peak height came from compounds other than 

 saturated hydrocarbons.* In figure 10, the resemblance is very good, and the 

 changes have been moderate, but as pointed out, the peaks in this series contain 

 substantial contributions from so many different sources, that it seems unsafe 

 to infer a similarity in parent hydrocarbon distribution from a similarity in 

 peak heights. 



Finally, one must not overlook the possibility that the observed hydrocarbon 



* This sample is not strictly comparable to the original distillate, collected in the range 

 250° to 400° C, because it also contains the 400° to 500° C. fraction. But differences of the 

 same order are found between the original distillate and a chromatographically separated 

 hydrocarbon fraction of a solvent extract of the whole meteorite (Meinschein et al., 1962). 



