English: In the Paleoproterozoic, the water column possibly became sulfidic and anoxic. Purple and green sulfur bacteria likely thrived in this euxinic environment. Purple sulfur bacteria produce the pigment okenone which, during diagenesis, degrades to okenane. Green sulfur bacteria with green pigments produce chlorobactene, which is altered to chlorobactane during burial. Green sulfur bacteria with brown pigments produce isorenieratene, which is preserved as isorenieratane. Each anoxygenic phototroph occupies a different depth range in the ocean, based on their pigment's light absorption. Biomarkers from these species may teach us about anoxic paleoenvironments.