The early Earth’s atmosphere was devoid of oxygen, but Archean rocks paradoxically documented oxidative weathering on the landmass of the same age. New research from the Guangzhou Institute of Geochemistry of the Chinese Academy of Sciences sheds light on a previously unrecognized source of abiotic oxidants in the oxidation of Earth’s Archean surface.

It is believed that biological O₂ released by oxygen-producing photosynthesis of cyanobacteria triggered the rise of atmospheric O₂ level to 10^–5 of the present atmospheric level in a catastrophic increase of the atmospheric O₂ called the Great Oxidation Event (GOE). Recently, increasing geochemical evidence indicated that Archean oxidation might have happened much earlier, even before the evolution evolving of biogenic O₂. However, the source of the oxygen remains a mystery.

In a recent study published in April in Communications Earth & Environments, an international team of scientists from the Guangzhou Institute of Geochemistry, the Chinese Academy of Sciences, The University of Hongkong, and the University of Alberta has answered this question. Building on the team’s earlier discovery of an abiotic pathway for Archean oxidant production at the abraded quartz-water interface (Nature Communications, 2021), they have expanded the oxygen-producing mechanism to include oxidation of H₂O to hydrogen peroxide (H₂O₂) by mechanically induced surface radicals on silicate minerals.

The team found that reactive oxygen species (ROS) can be produced during various silicate-water reactions, with the extent of ROS production increasing from mafic- to felsic-silicates. Weathering and denudation of mountains by rivers in early Archean continents (e.g., in the Kaapvaal and Pilbara Cratons) may have served as an effective “oxygen-producing factory”, providing at least 1.73×10⁸ moles of O₂ every year even before the development of biological O₂ production (Figure 1). They further proposed that ROS production should have increased in the Late Archean with the increased land area and physical weathering along with the transition from mafic to felsic continental crust.

The team’s research indicates that redox-sensitive elements may have been oxidatively mobilized into seawater prior to the GOE, increasing the availability of bio-essential nutrients to the Archean biosphere. Importantly, this ubiquitous abiotic oxygen-producing process linked the coevolution of the lithosphere and biosphere.