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

It is suggested that methane was the dominant carbon-bearing component of t he primary atmosphere of Mars. In this atmosphere CO2, being a minor compon ent, 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. Eventual ly, C-13-enriched carbonates became a source of atmospheric CO2. (C) 2000 A cademic Press.