Abstract
Oxygenic photosynthesis appears to be necessary for an oxygen-rich atmosphere like Earth's. But available geological and geochemical evidence suggest that at least 200Myr, and possibly more than 700Myr, elapsed between the advent of oxygenic photosynthesis and the establishment of an oxygen atmosphere. The interregnum implies that at least one other necessary condition for O2 needed to be met. Here we argue that the second condition was the oxidation of the surface and crust to the point where O2 became more stable than competing reduced gases such as CH4. The cause of Earth's surface oxidation would be the same cause as it is for other planets with oxidized surfaces: hydrogen escape to space. The duration of the interregnum would have been determined by the rate of hydrogen escape and by the size of the reduced reservoir that needed to be oxidized before O2 became favored. We suggest that continental growth has been influenced by hydrogen escape, and we speculate that, if there must be an external bias to biological evolution, hydrogen escape can be that bias.
Highlights
An oxygen atmosphere raises two issues that are not always separated
It could be that abundant free oxygen in the atmosphere oxidized the surface, or it could be that oxidation of the surface allowed abundant free oxygen to endure
It has long been considered probable from hints in the geological record that oxygenic photosynthesis appeared much earlier than widespread crustal oxidation (Holland, 1962; Buick, 2008), and that surface oxidation played a role in the rise of oxygen (e.g., Berkner and Marshall, 1965)
Summary
An oxygen atmosphere raises two issues that are not always separated. One is the matter of abundant O2, which is the distinctive feature of Earth's atmosphere. Oxygen and oxidation are different things and reflect different processes acting on different time scales, it is plausible that one is prerequisite to the other. The view taken here is that surface oxidation is prerequisite to O2. It has long been considered probable from hints in the geological record that oxygenic photosynthesis appeared much earlier than widespread crustal oxidation (Holland, 1962; Buick, 2008), and that surface oxidation played a role in the rise of oxygen (e.g., Berkner and Marshall, 1965). We explicitly tie the time it took to oxidize the surface through hydrogen escape to the time taken between the origin. Zahnle et al / Chemical Geology 362 (2013) 26–34 of oxygenic photosynthesis and the establishment of an oxygen atmosphere (Catling et al, 2001; Claire et al, 2006)
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