On the phenomenon of enrichment of Mars in 13C:: A suggestion on the reduced initial atmosphere

It is suggested that methane was the dominant carbon-bearing component of the primary atmosphere of Mars. In this atmosphere CO2, being a minor component, became enriched in C-13 due to isqtopic exchange with methane. In the presence of water CO2 was deposited as carbonate. Subsequently the methane atmosphere was lost to outer space possibly due to impact erosion. Eventually, C-13-enriched carbonates became a source of atmospheric CO2. (C) 2000 Academic Press.