Fig. 2.

Compound specific and bulk organic δ¹³C data. Stable carbon isotopic measurements of bulk organic matter from AIDP-2 and RHDH2A (3, 39) are compared (Center). The RHDH2A depth was converted to the AIDP-2 depth scale by a correction factor of 45 m due to the stratigraphic offset (see Fig. 1). Rock extract and HyPy full scan chromatograms are plotted with compound-specific isotopic analysis (CSIA) of PAH δ¹³C. AIDP-2 133.55 m (SI Appendix, Fig. S3) is the only sample that displayed an isotopic match between the extractable PAHs and the bulk organic matter (Top Right). The extractable PAH δ¹³C from the other Carawine Dolomite samples diverged from the corresponding bulk organic matter δ¹³C (Top Left). The hydropyrolysate PAHs from the Carawine Dolomite and the Jeerinah Formation match the bulk organic carbon isotopic composition (Bottom Left and Bottom Right). The range of previously published (Pub.) Archean PAH δ¹³C is plotted for reference (21, 24, 25). The analytical uncertainty is plotted for the PAH δ¹³C measurements, but it is smaller than the symbol in most cases. The different GC methods yield different retention times.