September 9, 2009 ESSC Brown Bag/Climate Dynamics Seminar

Production of oxidants by photochemistry and lightning in the anoxic Archean atmosphere

Dr. Jim Kasting
Penn State

Earth’s atmosphere prior to 2.4 billion years ago is generally believed to have had very low O2 concentrations. Yet, biologists have argued that O2 reductases, and possibly aerobic respiration itself, preceded the origin of oxygen-producing cyanobacteria, requiring an abiotic source of O2. Possible tropospheric O2 sources include disproportionation of photochemically produced H2O2 and thermal dissociation of CO2 in lightning bolts. Neither of these sources appears capable of producing enough O2 to sustain aerobic respiration in organisms. However, downward transport of stratospheric O2 in the wintertime polar night region, where O2 should have been long-lived, may have provided enough O2 for respiration.