Two major accumulation events are classically thought to highlight the rise of molecular oxygen (O2) on Earth. The first, the “Great Oxidation Event” (GOE), marks the initial rise of O2 above trace levels in Earth’s atmosphere. The second, the “Neoproterozoic Oxygenation Event” (NOE), perhaps marks the initial spread of O2 throughout Earth’s deep oceans. In this talk, I will discuss datasets generated by my co-authors and I (and others) that challenge the classical narratives of these ‘events’. According to our data, O2 was more abundant before the GOE, and the GOE itself was more dynamic than classically thought. Vice-versa, O2 was probably less abundant during the NOE, and the NOE was probably less dynamic than classically thought. Many of these viewpoints are bolstered, and some even shaped, by the recently developed thallium (Tl) isotope paleoredox proxy.

Dr. Chadlin (“Chad”) Ostrander is an Assistant Professor at the University of Utah in Salt Lake City. Chad’s research focus is ancient oxygen (more or less). He is a heavy metal stable isotope geochemist by training and a paleoceanographer by interest. He studies modern isotope cycles and uses this information to infer isotopic changes in the ancient marine sedimentary record. Chad received his B.S. and Ph.D. from Arizona State University and did his postdoctoral studies at Woods Hole Oceanographic Institution.