Isotope fractionations in the terrestrial carbon cycle:  a brief overview.
The bias in favour of isotopically light carbon inherent in biological carbon fixation has brought about an isotopic disproportionation of primordial (mantle-derived) carbon on a global scale, causing an enrichment of 12C in reduced (biogenic) carbon and a concomitant accumulation of the heavy complement (13C) in the residual oxidized (inorganic) carbon pool.  As a result, the terrestrial carbon cycle has gone bipartite, comprising an organic branch of isotopically light carbon, and an inorganic branch made up of 13C-enriched carbon (mostly in the form of carbonate).  The isotopic disparity between the two principal terrestrial carbon species can be traced back over 3.8 Gyr of Earth history, attesting to a biological modulation of the carbon cycle since the time of formation of the oldest sediments.
Schidlowski
M
M
Max-Planck-Institut für Chemie, Mainz, Germany.
D018533:Biomass; D002244:Carbon / Q000737:chemistry*; D002247:Carbon Isotopes; D002254:Carbonates; D005591:Chemical Fractionation; D018534:Earth, Planet; D019015:Geologic Sediments / Q000032:analysis*; D007700:Kinetics; D008956:Models, Chemical; D010788:Photosynthesis
D002247:Carbon Isotopes; D002254:Carbonates; D002244:Carbon