Recently,many carbon isotopic investigations for the mantle samples,such as diamond,kimberlites,carbonatites,oceanic basalts and mantle xenoliths,have shown that a very concentrated distribution is around -5‰,and a relatively weak distribution is from about -15‰ to -25‰ in the mantle carbon isotopes.This type of carbon isotopic distributions is difficult to explain by the current hypotheses,such as phase transformation of carboniferous matters,subduction of sedimentary carbon or mantle degassing,and so it is possible that the primordial mantle is heterogeneous in carbon isotopes.