Determining the concentration of carbon dioxide in the ancient atmosphere remains a critical hurdle to understanding Earth surface temperatures, compositional changes in atmospheric chemistry, and the evolution of Earths earliest biosphere. Kah and Riding report the finding of petrographic fabrics in 1.2-billion-year-old carbonate strata that suggest the process of cyanobacterial calcification. When ambient atmospheric partial pressure of CO2 (pCO2) concentrations fall below roughly 10 times present atmospheric levels (PAL), cyanobacteria begin to use a combination of dissolved carbonate species (CO32- and HCO3-) in the photosynthetic production of organic matter. The cyanobacteria, however, must perform a series of biochemical gymnastics to utilize HCO3- in this process. As a byproduct of these biochemical changes, the pH of the microbial sheath rises dramatically and induces the precipitation of calcium carb
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| Contact: Ann Cairns acairns@geosociety.org 303-357-1056 Geological Society of America Source:Eurekalert |