Relationship between photosynthesis and banded iron formations at the early Archean

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Diagenetic chromium oxides were newly found in banded iron formations at 3. 2 Ga Barberton Greenstone Belt, South Africa. Oxygenisotopeanalyses of chromium oxides suggest oxygen from photosynthesis was responsible for oxidation and precipitation of chromium. By studying banded iron formations at Lumby Lake area, Canada, many geological samples recoded the evidence of oxygenic photosynthesis and activities of chemoautotrophs. In particular,"chemoautotrophic" rocks were found to be formed under t he influence of submarine hydrothermal activities. In other words, photosynthesis was widespread at the surface oceans and bottom was dominated by chemoautotrophs at 3. 0 Ga.