Table 1 Assumed initial atmosphere-ocean composition for Archean and Proterozoic.
Archean rangeProterozoic range
Atmospheric
species
Mixing ratioReference/explanationMixing ratioReference/explanation
Minimum
disequilibrium
Maximum
disequilibrium
Minimum
disequilibrium
Maximum
disequilibrium
N2(g)0.980.5Mixing ratios sum to 10.990.86Mixing ratios sum to 1
O2(g)1 × 10−102 × 10−7(39)0.00010.03(14, 76)
CH4(g)0.00010.01(77)3 × 10−61 × 10−4(78, 79)
CO2(g)0.0010.5(80, 81)0.00010.1(80, 81)
H2(g)00.0001(59)02 × 10−6(82)
N2O(g)00No denitrification so negligible production01 × 10−6(79, 83)
NH3(g)01 × 10−9(84)00Negligible in bulk atmosphere
O3(g)00Negligible in bulk atmosphere00Negligible in bulk atmosphere (79)
CO(g)00.001(59)02 × 10−7(82)
Ocean speciesMolality (mmol/kg)Reference/explanationMolality (mmol/kg)Reference/explanation
Minimum
disequilibrium
Maximum
disequilibrium
Minimum
disequilibrium
Maximum
disequilibrium
Na+550586Charge balance547549Charge balance
Cl546546Modern value546546Modern value
Embedded Image00.2(85, 86)0.255(87, 88)
H2S00.004In euxinic oceans using a Black Sea analog*00.004In euxinic oceans using
a Black Sea analog*
Embedded Image00.050Set by phosphorus assuming Redfield ratios and
the presence of N fixation, given that N fixation
evolved early (89)
00.050Set by phosphorus
assuming Redfield ratios
Embedded Image00Anoxic bulk ocean00Anoxic bulk ocean
Alkalinity440(29); Krissansen-Totton et al., in preparation1.03.0(29); Krissansen-Totton
et al., in preparation
pH8.06.3Carbon chemistry equilibrium8.46.0Carbon chemistry
equilibrium

*The concentration of H2S in the Black Sea is around 400 μmol/kg (90). However, <1 to 10% of the Precambrian seafloor was euxinic (91), which implies <1% euxinia by volume because euxinic continental slopes are much shallower than the deep ocean. Thus, we assumed 4 μmol/kg as an upper limit for bulk ocean aqueous H2S.

†The maximum subsurface concentration of Embedded Image is ultimately controlled by flux of phosphate from continental weathering. Assuming a modern dissolved phosphate abundance of ~2 μmol/kg, this implies an ammonium abundance of 32 μmol/kg assuming a 1:16 Redfield ratio. Results are largely insensitive to initial abundances of Embedded Image (Fig. 5).

‡pH is calculated from alkalinity and Pco2 assuming chemical equilibrium.