Scripps Institution of Oceanography at UC San Diego presents the Tsaihwa "James" Chow Lecture series March 30 and 31.
Join us as Professor Daniel P. Schrag of Harvard University presents his second lecture, "Geochemical Dynamics of Atmospheric Oxygen," March 31 at Sumner Auditorium. Talk begins at 2:00 p.m. Snacks will be served following the lecture.
Description: Geological records of atmospheric oxygen suggest that pO2 was less than 0.001% of present atmospheric levels (PAL) during the Archean, increasing abruptly to a Proterozoic value between 0.1-10% PAL, and rising quickly to modern levels in the Phanerozoic. Using a simple model of the biogeochemical cycles of carbon, oxygen, sulfur, hydrogen, iron and phosphorous, Dr. Schrag and colleagues demonstrate that there are three stable states for atmospheric oxygen, roughly corresponding to levels observed in the geological record. These stable states arise from a series of positive and negative feedbacks, requiring a large geochemical perturbation to the redox state to transition from one to another. They show that the "Snowball Earth" glaciations, which immediately precede both transitions, provide the appropriate transient increase in atmospheric oxygen to drive the atmosphere either from its Archean state to its Proterozoic state, or from its Proterozoic state to its Phanerozoic state. This hypothesis provides a mechanistic explanation for the apparent synchronicity of the Proterozoic Snowball Earth events with both the Great Oxidation Event, and the Neoproterozoic oxidation. It also offers an alternative view of the history of life on Earth, questioning the inevitability of oxygenation of Earth’s surface. A remaining mystery is the cause of the Paleozoic rise in oxygen, which has been attributed to the evolution of land plants.
Learn more about Dr. Schrag at https://eps.harvard.edu/people/daniel-schrag.
Download the event flyer here.
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