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Globally averaged authigenic H2 production on early Mars. As surface and subsurface water reservoirs interact on early Mars and trigger authigenic magnetite precipitation, atmospheric H2 concentration increases to percent levels over timescales of 104 to 105 years or less. Lines indicate atmospheric H2 concentrations calculated at various percentages of the early Martian surface hosting authigenic H2 production. Calculations apply a constant H-escape rate for H2-bearing atmospheres17.
