Using a new photochemical model, the HCN chemistry in Earth's early atmosphere is revisited. We find that HCN production in a CH4-rich early atmosphere could have been efficient, similar to the results of a previous study (Zahnle, 1986). For an assumed CH4 mixing ratio of 1000ppmv, HCN surface deposition increases from 2×109cm-2s-1 at fCO2=3% to more than 1×1010cm-2s-1 (30Tg/yr) at fCO2=0.3% and 1%. These conditions may well have applied throughout much of the Archean eon, 3.8-2.5Ga. Prior to the origin of life and the advent of methanogens, HCN production rates would likely have been at 1×107cm-2s-1 or lower, thereby providing a modest source of HCN for prebiotic synthesis.
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology
- Earth and Planetary Sciences (miscellaneous)
- Space and Planetary Science