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Supercontinents, supermountains and the rise of atmospheric oxygen

Ian Campbell and Charlotte Allen

1 Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia

Figure 1.Supercontinent ages compared with variations in atmospheric O2 and related variables. (a), Tonnes of P 2 O5 in phosphate deposits and Fe in iron formations. (b), 13δC in marine carbonates (red) and 34 δS in sulfate (green).  Black lines correspond to ice ages. (c), 87Sr/86Sr in seawater. (d), Atmospheric O2 showing the steps described in the text. Arrows point to periods of low atmospheric O2. e, U/Pb ages of 5246 concordant detrital zircons from 40 major rivers supplemented by 1136 Australian dune zircons and 583 from Antarctic Palaeozoic sediments.

Atmospheric oxygen concentrations in the Earth’s atmosphere rose from negligible levels in the Archaean Era to about 21% at present day.  This increase is thought to have occurred in six steps, 2.65, 2.45, 1.8, 0.6, 0.3 and 0.04 billion years ago, with a possible seventh event identified at 1.2 billion years ago.  The timing of these steps correlates with the amalgamation of Earth’s landmasses into supercontinents.  We suggest that the continent-continent collisions required to form supercontinents produced chains of supermountains. These supermountains eroded quickly and released large amounts of nutrients such as iron and phosphorous into the oceans, leading to an explosion of algae and cyanobacteria, and thus a marked increase in photosynthesis, and the photosynthetic production of O2.  Enhanced sedimentation during these periods promoted the burial of a high fraction of organic carbon and pyrite, thus preventing their reaction with free oxygen, and leading to sustained increases in atmospheric oxygen.