This session will focus on textural and geochemical evidence for evolving microbial ecosystems on the early Earth. We welcome studies of candidate biosignatures from the Archean rock record and potential habitats available to life in ancient greenstone belts. We also solicit geochemical and geomicrobiological studies that investigate the biogeochemical evolution of the Archean to Proterozoic Earth. These could include, but are not limited to, studies of evolving ocean-atmosphere redox states and evidence for the first whiffs of oxygen. In addition, we seek presentation of new approaches from fields such as microscopy, microanalysis, climate modeling and isotope geochemistry as used to reconstruct ancient ecosystems on the early Earth and potentially Mars.