XVI International Botanical Congess

Organic carbon (Corg) is the sine qua non for life. A challenge for life is to obtain Corg. The evolutionary sequence of Corg acquisition was 1) the abiotic production of Corg from inorganic precursors, 2) the emergence of life from organic precursors, 3) the use of available abiotically-produced Corg, 4) the selection for organisms that produce Corg from inorganic precursors, 5) the evolution of herbivory in a broad sense, and 6) the evolution of carnivory. Photosynthesis probably arose early in evolution. We model early carbon cycling by measuring photosynthesis in modern analogs for ancient ecosystems. We measure gross rates of photosynthesis, diurnal patterns of photosynthesis, and the effect of early high levels of pCO2 and high UV radiation fluxes on photosynthesis. This work has shown that geochemical cycling of carbon in the Precambrian was likely to have been different from modern ecosystems.