Long-term evolution of terrestrial weathering and its link to Earth's oxygenation

Terrestrial weathering releases phosphorus and other essential nutrients that fuel life in Earth's surface environments and sustain oxygenic photosynthesis. Despite previous suggestions that major changes in terrestrial chemical weathering might have played a role in the global oxygen cycle in the geological past, little is known about the Earth's weathering history. To date, the cause-and-effect relationship between weathering and the long-term evolution of atmospheric oxygen, and whether chemical weathering became more efficient after the initial rise of atmospheric oxygen in the early Paleoproterozoic, remained largely elusive. Here we report a reconstruction of the intensity of terrestrial weathering for the last 2.7 billion years, based on coupled neodymium-hafnium isotope (ΔεHf(i)CLAY) and elemental analyses of the fine-grained clay-size fraction of shales. A pronounced shift towards higher ΔεHf(i)CLAY values and rubidium/aluminium (Rb/Al) ratios indicates that preferential dissolution of phosphate-bearing minerals and biotite intensified between ∼2.5 and 2.4 billion years ago (Ga), following the emergence of continental landmasses and coinciding with the initiation of the Great Oxidation Event. After a long time interval characterized by a constant degree of low-intensity chemical weathering, between ∼2.3 to 0.7 Ga, terrestrial weathering further accelerated after the Neoproterozoic glaciations at ∼0.6 Ga, as inferred from markedly decreased Rb/Al ratios, coincident with the second rise of atmospheric oxygen. These findings support a link between the long-term intensity of chemical weathering and atmospheric oxygen level since the late Archean. We further propose that the 100-million-year-long period of enhanced terrestrial weathering from ∼2.5 Ga played a major role, via crustal recycling of phosphorus and export to the surface ocean, in the early expansion of the aerobic biosphere that ultimately led to the Great Oxidation Event