Early oxygenation of the terrestrial environment during the Mesoproterozoic

Geochemical data from ancient sedimentary successions provide evidence for the progressive evolution of Earth’s atmosphere and oceans1, 2, 3, 4, 5, 6, 7. Key stages in increasing oxygenation are postulated for the Palaeoproterozoic era (~2.3 billion years ago, Gyr ago) and the late Proterozoic eon (about 0.8 Gyr ago), with the latter implicated in the subsequent metazoan evolutionary expansion8. In support of this rise in oxygen concentrations, a large database1, 2, 3, 9 shows a marked change in the bacterially mediated fractionation of seawater sulphate to sulphide of Δ34S