What triggered the Great Oxidation Event (GOE) on Earth? New insights from the Cerium redox state in Precambrian sediments

About 2.4 Ga ago, the Earth transitioned from an anoxic to an oxygen-rich world through the Great Oxidation Event (GOE). The origin and precise timing of this event remain still highly debated in the Earth Science community. The study of Cerium (Ce) may be key to solve major questions around the GOE as we recently demonstrated that Ce stable isotopes were not fractionated the same way in seawater precipitates formed before and during the GOE. We hypothesized that a stronger isotopic fractionation occurred in oxygen-rich seawater, when Ce got oxidized from +III to +IV onto Fe-oxide precipitates. The use of XANES to probe the redox state of Ce into different mineral phases in the pre and syn-GOE sediment samples is crucial to test this hypothesis. The preservation of a higher Ce4+/ Ce3+ ratio in the syn-GOE samples will undoubtedly establish Ce stable isotopes a novel redox tracer to strengthen our knowledge of the oxygenation state of the past oceans in the early Earth.