Availability of O(2) and H(2)O(2) on pre-photosynthetic Earth - PubMed (original) (raw)

Availability of O(2) and H(2)O(2) on pre-photosynthetic Earth

Jacob Haqq-Misra et al. Astrobiology. 2011 May.

Abstract

Old arguments that free O(2) must have been available at Earth's surface prior to the origin of photosynthesis have been revived by a new study that shows that aerobic respiration can occur at dissolved oxygen concentrations much lower than had previously been thought, perhaps as low as 0.05 nM, which corresponds to a partial pressure for O(2) of about 4 × 10(-8) bar. We used numerical models to study whether such O(2) concentrations might have been provided by atmospheric photochemistry. Results show that disproportionation of H(2)O(2) near the surface might have yielded enough O(2) to satisfy this constraint. Alternatively, poleward transport of O(2) from the equatorial stratosphere into the polar night region, followed by downward transport in the polar vortex, may have brought O(2) directly to the surface. Thus, our calculations indicate that this "early respiration" hypothesis might be physically reasonable.

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Figures

FIG. 1.

FIG. 1.

Vertical profiles of O2 volume mixing ratio at CO2 partial pressures of 0.02, 0.2, and 2.0 bar. These profiles are calculated with a one-dimensional photochemical model with an H2 outgassing rate _Φ_out(H2) = 1010 cm−2 s−1.

FIG. 2.

FIG. 2.

Vertical profiles of H2O2 volume mixing ratio for the three model atmospheres shown in Fig. 1.

FIG. 3.

FIG. 3.

Fraction of tracer _ξ/ξ_0 at the surface 180 days after northern autumnal equinox (left panel) and northern winter solstice (right panel). Both simulations assume dry conditions and include topography.

FIG. 4.

FIG. 4.

Fraction of tracer _ξ/ξ_0 at the surface 180 days after northern winter solstice under dry conditions with doubled spectral resolution.

Comment in

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