The metabolic repertoire of different microbial lineages often provides us with patterns that reveal how life navigated alternative environmental landscapes. In many cases, however, metabolic strategies are shared among closely interacting microbial populations, and thus critical evolutionary information may be stored, like pieces of a puzzle, in separate members of a microbial community. I therefore suggest that considering microbial interactions in the establishment of novel biochemical pathways can open new windows through which to understand how the physiology of microbes evolved. As part of a NASA Postdoctoral Program Fellowship, I’m using a synthetic microbial community to determine if heterotrophic proteobacterial partners would have helped Cyanobacteria resist reactive oxygen species during the evolution of oxygenic photosynthesis in iron-rich early Earth oceans. Results from this study will illuminate eco-evolutionary processes behind metabolism, and may allow us to infer communal biochemistries on Earth and potentially on other planets.