The Archean atmosphere

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Science Advances  26 Feb 2020:
Vol. 6, no. 9, eaax1420
DOI: 10.1126/sciadv.aax1420


  • Fig. 1 Precambrian events and atmospheric change.

    For biological evolutionary dates, see (6). For a description of other events, see (64) and references therein.

  • Fig. 2 Schematic histories of atmospheric O2 and surface barometric pressure or N2.

    (A) Colored arrows faithfully represent known O2 constraints, but the black line is speculative. An Archean upper bound of <0.2-μbar O2 (blue) is for photochemistry that generates S8 aerosols, preserving observed mass-independent isotope fractionation in sulfur compounds (44). The size and shape of an O2 overshoot during the GOE are highly uncertain; a lower bound (red arrow) comes from iodine incorporation into carbonates (251). In the Proterozoic, a lower bound (light green) of 6 × 10−4 bar is required for an O2-rich atmosphere to be photochemically stable (44). However, O2 levels likely remained low for most of the Proterozoic (252). Neoproterozoic oxygenation began around ~800 Ma ago. From ~600 Ma ago, a lower bound of >0.02-bar O2 (dark green) is from plausible O2 demands of macroscopic Ediacaran and Cambrian biota (120). Charcoal since 0.4 Ga ago implies a lower bound of >0.15 bar (purple) (253). The post-Devonian black line for O2 evolution approximately represents curves from calculations of C and S isotopic mass balance (254, 255). (B) Constraints on surface atmospheric pressure (red) (56, 57) and the partial pressure of nitrogen, pN2 (blue) (48, 49, 140). Blue shading shows a schematic and speculative pN2 range in different time intervals consistent with very sparse proxy data.

  • Fig. 3 History of CO2 and a CH4 schematic since the Archean.

    (A) The black line is median CO2 from a carbonate-silicate climate model, and yellow shading indicates its 95% confidence interval (34); this curve merges with a fit to CO2 proxy estimates for 0.42 Ga ago to present from (256). Various Precambrian pCO2 proxy estimates are shown (42, 43, 168, 257259). (B) A very schematic history of CH4. Constraints include a lower limit (blue) required for Archean S-MIF (44) and a tentative lower limit of ~3.5 Ga ago from a preliminary interpretation of xenon isotopes (black) (187). The black curve is from a biogeochemical box model coupled to photochemistry (121). Orange shading is schematic but consistent with possible biological CH4 fluxes into atmospheres of rising O2 levels at the GOE and in the Neoproterozoic. Note that the suggestion that moderately high levels of methane may have contributed to greenhouse warming in the Proterozoic (260, 261) has been disputed (262, 263) and may depend on fluxes from sources on land (264). The curve for ~0.4 Ga ago to present is from (265).

  • Fig. 4 Mass fractionation of nine atmospheric xenon isotopes over time relative to modern air per atomic mass unit showing relative enrichment in light isotopes in the past.

    Data from (49). The vertical axis shows the fractionation per atomic mass unit (amu) of atmospheric xenon relative to modern air. To compute this average fractionation across the nine isotopes, Avice and co-workers (49) normalized the isotopic compositions to 130Xe and to the isotopic composition of the modern atmosphere using the delta notation. For a Xe isotope of mass i, δiXeair = 1000 × ((iXe/130Xe)sample/(iXe/130Xe)air − 1). The slope of a straight line fit to the normalized data provides the average fractionation per atomic mass per unit and its uncertainty, i.e., plotted points. Inset: A diagram showing schematically how the slope of the fractionation of the nine isotopes changed over time relative to the initial solar composition, where the graph is normalized to atomic mass 130.

  • Fig. 5 An overview of post-Archean atmospheric evolution in the context of biological evolution and constraints on mean global temperature in the Archean (see text) in the context of the glacial record.

    (A) Uncertainties on gas concentrations are a factor of a few or more as detailed in Table 1, the text, and the other figures. Dinitrogen may have tracked O2 levels due to an oxidative weathering and denitrification source of N2, but pN2 changes are debated. Methane was oxidized as O2 rose but could have been protected subsequently under an ozone layer, depending on post-Archean CH4 source fluxes. The secular decline of CO2 is a feedback effect in the geological carbon cycle induced by decreasing solar luminosity. (B) Constraints on Archean mean global temperature. Vertical blue bars denote that glacial rocks exist, noting that the durations of glaciations in the early Proterozoic and earlier are poorly known. Neoproterozoic and Phanerozoic glaciation ages are from (266, 267). A proposed Mesoproterozoic glaciation (268) is not plotted because its age is disputed and possibly Sturtian (269). Cenozoic glaciations only occur at a global mean temperature below ~20°C. Red arrows on the Archean glaciations are a more conservative 25°C upper limit, taking into account of the possible effects of different land configurations and lack of vegetation. Low CO2 during the Phanerozoic (A) correlates with glaciations (B), such as Carboniferous-Permian ones, 335 to 256 Ma ago. Precambrian greenhouse gases must also have fluctuated, but the amount is unknown and so not reflected in (A).


  • Table 1 Archean environmental constraints.

    Constraints on atmospheric gases at ground level (unless stated otherwise) and some bulk marine species. Gas level constraints are given in the same units as in the cited papers: partial pressure in bar or atm, where 1 bar = 0.9869 atm, or as mixing ratios (ppmv = parts per million by volume; S-MIF = sulfur isotope mass-independent fractionation).

    Archean atmospheric gases
    Parameter or speciesPublished constraintAge (years before present)Basis of constraint
    O2<10−6 × present O2>2.4 GaModeled S8 flux needed to create and carry S-MIF (44)
    <3.2 × 10−5 atm2.415 GaDetrital uraninite (66), if the river length feeding
    the Koegas subgroup is accurately estimated
    O3 column<1015 molecules m−2>2.4 GaModeled for ground-level O2 < 0.2 ppmv (44, 270)
    Surface barometric pressure<0.52–1.1 bar2.7 GaMaximum fossil raindrop imprint size (57)
    0.23 ± 0.23 bar (2σ)2.74 GaFossil vesicles at the top and base of basaltic lavas (56)
    N2<1.1 bar (2σ)3.5–3.0 GaN2/36Ar in fluid inclusions (48)
    <1 bar (2σ)3.3 GaDerived from Fig. 4A and Table 2 of Avice et al. (49).
    HCNUp to ~100 ppmv>2.4 GaPhotochemistry if CH4 was ~103 ppmv (166, 167)
    N2O~Few ppbv>2.4 GaLightning production of NO and HNO in a reducing
    atmosphere, dissolution of HNO, and evaporation
    CO2>0.0004 bar (0°C),
    >0.0025 bar (25°C),
    >0.26 bar (100°C)
    3.2 GaSiderite weathering rinds on river gravel (257)
    0.03–0.15 bar2.77 GaMt. Roe paleosol, Australia (43)
    0.02–0.75 bar2.75 GaBird paleosol, South Africa (43)
    0.003–0.015 bar2.69 GaAlpine Lake paleosol, MN, United States (168)
    0.05–0.15 bar2.46 GaPronto/NAN paleosol, Canada (43)
    <~0.8 bar3.8–2.4 GaEnough UV to make S-MIF (58)
    CH4>20 ppmv>2.4 GaLower limit for sufficient reductant for S-MIF (44)
    >~5000 ppmv~3.5 GaEnough methane to induce sufficiently rapid hydrogen
    escape to drag Xe+ and fractionate Xe isotopes (187)
    COLess than a few ppmvAfter the origin of
    CO consumers
    Thermodynamic limit if microbes used available free energy
    of CO [appendix A of Krissansen-Totton et al. (250)]
    <300 ppmvLimit if transfer of gas through the atmosphere-ocean
    interface restricts CO consumption (183).
    H210 s–100 ppmvAfter the origin
    of methanogens
    Assuming that methanogens used available free energy
    from consuming H2 (197, 271) and the transfer of gas
    through the atmosphere-ocean interface restricts
    H2 consumption (183).
    <0.01 bar3.0–2.7 GaThe survival of detrital magnetite in rivers, if Fe3+-reducing
    microbes are assumed (200)
    Archean seawater species
    At 4 Ga
    At 2.5 Ga
    95% confidence ranges from a carbon cycle model
    with 104-ppmv Archean CH4 (34).
    SO42−(aq) (bulk sea)<2.5 μM>2.4 GaLack of mass-dependent sulfur isotope fractionation (75)
    NO3(aq) (bulk sea)~0>2.4 GaBy analogy to the deep, anoxic Black Sea (272)
    NH4+(aq)0.03–10.3 mM
    (probably porewater
    rather than seawater)
    ~3.8 GaFrom the N content of biotites (originally clays),
    derived from adsorption of dissolved NH4+(aq) (148)
    Fe2+(aq) (deep sea)40–120 μM (2–7 ppm by weight)>2.4 GaBased on solubility constraints of Fe2+ (139)
    Salinity (g/kg)~20–50 at 40°–0°C versus modern of 353.5–3.0 GaFrom seawater fluid inclusions in quartz (50)
    PotassiumCl/K ~50 versus modern 293.5–3.0 GaFrom seawater fluid inclusions in quartz (50)

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