Uranium isotope evidence for Mesoarchean biological oxygen production in shallow marine and continental settings

Xiangli Wang, Frantz Ossa Ossa, Axel Hofmann, Andrea Agangi, Dora Paprika, Noah J. Planavsky

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)


Oxidative weathering of continental rocks is the major source of redox-sensitive elements to the ocean. The timing for the initiation of oxidative weathering remains strongly debated. Here we report new δ238U data for the authigenic component of well-preserved ca. 3.07–2.90 Ga marine and lacustrine shales from the Mozaan and Dominion groups of the Kaapvaal Craton, South Africa. The δ238Uauth values in marine shales (−0.71‰ to −0.21‰ relative to CRM 112a) are lower than the bulk silicate Earth (BSE, −0.40‰ to −0.17‰), while those of lacustrine shales (−0.68‰ to 0.05‰) scatter above and below the BSE range. In addition, the δ238Uauth values of marine shales deposited in shallow seawater are significantly lower than those of the shales deposited in deep seawater. We propose that U(VI) was adsorbed onto Fe-Mn oxides in oxic shallow water and then shuttled to the seafloor. The U isotope fractionations in lacustrine shales are best explained by reduction of U(VI) to U(IV) below the sediment-water interface. Together, these observations bolster the case that a mildly oxidative weathering regime had been established at the Earth's surface by ∼3.0 Ga, paving the way to the onset of aerobic metabolism in both continental and shallow marine environments.

Original languageEnglish
Article number116583
JournalEarth and Planetary Science Letters
Publication statusPublished - 1 Dec 2020


  • Archean
  • oxygen
  • paleoredox proxy
  • photosynthesis
  • uranium isotopes

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science


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