Recent Advances in Geochemical Paleo-Oxybarometers

Knowledge of how and why oxygenic photosynthesis, eukaryotes, metazoans, and humans evolved on Earth is important to the search for complex life outside our Solar System. Hence, one grand challenge for modern geoscience research is to reconstruct the story of how Earth's environment and life coevolved through time. A critical part of the effort to understand Earth's story is the use of geochemical signatures from the rock record—paleo-oxybarometers—to constrain atmosphere and ocean O 2 levels and their spatiotemporal variations. Recent advances in analytical methods and improved knowledge of elemental and isotopic (bio)geochemical cycles have fostered development and refinement of many paleo-oxybarometers. Each offers its unique perspective and challenges toward obtaining robust (semi)quantitative O 2 estimates. Overall, these paleo-oxybarometers have provided critical new insights but have also spurred new debates about Earth's oxygenation and its impact on biological evolution (and vice versa). Integrated approaches with multiple paleo-oxybarometers are now more critical than ever. ▪ Paleo-oxybarometers estimate atmosphere or ocean O 2 levels, providing insight on how Earth's environment and life coevolved over time. ▪ Recent conceptual, analytical, and modeling advances, aided by studies on modern environments, have improved quantitative O 2 estimates. ▪ Atmosphere and ocean paleo-oxybarometers reveal a complex history of dynamic O 2 fluctuations since oxygenic photosynthesis evolved. ▪ Further improvements in the accuracy and robustness of atmosphere-ocean O 2 estimates will require more integrated approaches.