Along with Van Baalen and student John Calder, Parker noted that the carbon isotope fractionation between bulk tissue and dissolved CO2 measured in natural cyanobacterial mats and in algal cultures was highly variable and lower than that measured in Precambrian rocks (Calder and Parker, 1968). The significance of this work, that carbon isotopic compositions of organic matter could be proxies for palaeo-CO2 concentrations, was only realised much later. When I arrived in Texas, this quandary dominated the Parker-Van Baalen laboratories, since it was assumed that organic matter in Precambrian rocks originated from similar modern environments present...

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