Where do the anoxygenic photosynthetic bacteria fit into the broad evolutionary scheme?
Des Marais. Molecular evidence favors the scenario where non-oxygenic photosynthesis preceding oxygenic photosynthesis. These diverse earlier photosynthetic systems seem to have a common ancestry. Unfortunately, these earlier photosynthesizers are hard to detect in the geologic record. One of them, Chlorobium, leaves a distinctive organic biomarker. Cyanobacteria leave much more robust records as fossilized cells and as organic biomarkers. Rye. Getting back to the topic of the formation of oxidants, ferrous iron can also be oxidized by light-driven reactions in the absence of O2. Mojzsis. There was a lot of ultramafic rock around early. It was rich in iron, magnesium, nickel, chromium and some other transition metals. Today, such rocks (ophiolites) are being altered by waters that consequently become very alkaline (pH>10). This environment supports microorganisms but has been very poorly studied. Their study seems important for understanding the early biosphere. Woolf. Lets return to f
