Constraining Hadean mantle redox state using S-speciation in zircon-hosted apatite inclusions

The oxidation state of Earth’s upper mantle exerts a fundamental control on volcanic outgassing, atmospheric composition, and planetary habitability. Constraints on Hadean mantle redox are scarce and uncertain, relying entirely on Ce anomalies in a small number of zircons—a proxy limited by large uncertainties and potential arc-related biases. This project applies a novel approach by measuring S-speciation in zircon-hosted apatite inclusions from the Green Sandstone Bed and Jack Hills. Using μ-XANES, we will obtain high-precision fO₂ estimates with uncertainties an order of magnitude smaller than Ce-based methods. These data will provide the first S-based constraints on mantle redox prior to 3.8 Ga, anchoring models of oxidation mechanisms, outgassing, and convective mixing. By significantly improving the precision of early mantle redox reconstructions, this work will deliver transformative insights into Earth’s earliest environments and the conditions under which life may have formed.