Photoferrotrophic bacteria harness energy from sunlight to fix inorganic carbon into biomass while oxidizing ferrous iron. They thus populate illuminated, iron-rich (ferruginous) environments where they contribute to biogeochemical cycling of carbon, iron and many other elements. Though rare on Earth today, ferruginous conditions were the hallmark of the low oxygen oceans of the Precambrian eons. Photoferrotrophs likely populated these early ferruginous oceans driving primary production and supporting the Precambrian biosphere. Emerging insight from modern photoferrotrophic bacteria suggests that Precambrian photoferrotrophs could have played a pivital role in the evolution of atmospheric chemistry and life over billions of years of Earth’s early history. This seminar will present these recent advances and propose a new model for the evolution of Earth’s early atmosphere and life in the Precambrian eons.