Speaker Bios (Current Season)

June 11th, 2026

  Oxygenic photosynthesis is Earth's most important metabolism by any measure. While most would agree that it had evolved by the Great Oxidation Event ca. 2.5 to 2.3 billion years ago (Ga), the first putative traces of oxygenic photosynthesis, stretching back into the Archean, have been the subject of important debate. In this seminar I review sedimentary evidence for the operation of oxygenic photosynthesis ca. 3.2 to 2.5 Ga, with special attention to the fidelity of paleoredox signatures in Archean sedimentary records that have been subject to important diagenetic, metamorphic, and surface alteration processes. Special attention will be paid to paleoredox tracers that participate in radioactive decay systems, and thus their closure history may be directly interrogated by geochronology. In the second half of the talk, REE systematics and La-Ce geochronological data will be presented and discussed for three Archean microbialitic carbonate platforms from the Superior Craton. All three sites demonstrate important negative Ce anomalies indicating O2 production by oxygenic photosynthesis, and their La-Ce closure ages are consistent with known depositional ages previously constrained by zircon U-Pb geochronology. Together, these new data provide novel and robust geological support for an origin of oxygenic photosynthesis prior to 2.87 Ga.