Carbon Isotopic Studies of Organic Matter in Precambrian Rocks

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Science  17 Mar 1972:
Vol. 175, Issue 4027, pp. 1246-1248
DOI: 10.1126/science.175.4027.1246


Reduced carbon in early Precambrian cherts of the Fig Tree and upper and middle Onverwacht groups of South Africa is isotopically similar (the average value of δ13CPDB is -28.7 per mil) to photosynthetically produced organic matter of younger geological age. Reduced carbon in lower Onverwacht cherts (Theespruit formation) is anomalously heavy (the average value of δ13CPDB is -16.5 per mil). This discontinuity may reflect a major event in biological evolution.