THE EVOLUTIONARY GEOBIOLOGY OF EARTH'S OXYGEN CYCLE (Invited Presentation)

The amount of molecular oxygen (O₂) in Earth's ocean-atmosphere system has changed dramatically over time. Although a basic framework for the long-term evolution of ocean-atmosphere O₂ levels has long been appreciated, reconstructing the empirical trajectory of this evolution, the mechanisms underpinning it, and its cause-and-effect relationships with biological innovation represent central outstanding problems in the field of geobiology. Building on previous and ongoing work and drawing from the perspectives of stable isotope geochemistry, Earth system modeling, and experimental evolution, this talk will discuss three case studies centered on the links between biological innovation and evolving ocean-atmosphere O₂ levels on Earth: (1) the emergence and early biogeochemical impacts of oxygenic photosynthesis during the Archean and Paleoproterozoic; (2) the influence of ocean ventilation on nutrient levels and energy flow through algal ecosystems during the mid-Proterozoic; and (3) possible links between environmental O₂ levels and the evolutionary ecology early animal life.