Investigating the roles of Fe(II)-silicate and Fe(III)-silicate complexes and nanoparticles in the survival of early cyanobacteria and photoferrotrophic bacteria

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Life evolved on Earth nearly four billion years ago, but the environmental conditions surrounding its evolution remains poorly understood. Ancient microbial fossil and isotopic records indicate the existence of thriving photosynthetic microbial ecosystems by 3.5 Ga, and perhaps as early as 3.8 Ga. However, these environments presented high levels of UV radiation and toxic iron concentrations that should have made early marine environments inhospitable to life. The answer to how ancient photosynthetic bacteria (photoferrotrophs and cyanobacteria) overcame these environmental stresses possibly lies in the composition of Archean seawater itself. High silica abundances in pre-2.5 Ga seawater may have been instrumental in the initial survival of ancient photosynthetic bacteria, as well as to the early colonization of littoral marine environments, by forming Fe(II)-silicate and Fe(III)-silicate complexes and nanoparticles in the ancient water column. These complexes and nanoparticles would have not only acted as a ‘sunscreen’ against the high levels in incident UV radiation. By complexing with iron(II), silica would have lowered the level of dissolved, bioavailable and toxic iron(II) to more manageable levels, thus enabling the survival and evolution of early bacteria under high iron conditions. In this regard, the purpose of this proposal is twofold: i) to identify the geochemical composition and physical nature of the Fe(II)-silicate and Fe(III)-silicate complexes and nanoparticles, and ii) to determine their ability at protecting free-floating (planktonic) cyanobacteria and photoferrotrophs from long-term exposure to Archean-level UV radiation. By applying information derived from the Archean rock record, to geochemical and biological models, this multidisciplinary approach will allow the elucidation of a number of important interactions between the early hydro-litho- and atmosphere, and early life.