Photosynthesis Use of radioisotopes to Light 14CO2 measure microbia rporate activity in nature Dark (a) photosynthesis measured in natural Sulfate reduction in mud seawater with 14c02 H2 present H35S (b) Sulfate reduction in mud measured with 35SO4 H≥ absent () Time (c)Methanogenesis Methanogenesis in mud measured in mud with 14CH. COO acetate labeled in either 14cH4 the methyl(CH3 c00-) or the carboxyl CH14CO0 Time (CH3 4C00-)carbonUse of radioisotopes to measure microbial activity in nature. (a) Photosynthesis measured in natural seawater with 14CO2 (b) Sulfate reduction in mud measured with 35SO4 2- (c) Methanogenesis measured in mud with acetate labeled in either the methyl (14CH3COO- ) or the carboxyl (CH3 14COO- ) carbon