The onset of oxidative weathering traced by uranium isotopes

•Substantial new U isotope data from Archean and Early Proterozoic sediments.•Onset of oxidative weathering of U minerals indicated at ∼2.5 Ga.•Initial oxidative continental weathering resulted in preferential release of 235U.•235U accumulated in the uppermost slightly oxic water column of a stratified ocean.•Uranium behaved non-conservatively due to the overall anoxic conditions.•Abrupt decrease in U isotope ratio variability at 2.3 Ga.•Ending of the GOE and onset of (modern-style) weathering at 2.3 Ga.