Animal migrations mark the largest daily movement of biomass on Earth today, but who performed the first diurnal migration? Extant benthic microbial mats inhabiting Lake Huro’s low-oxygen, high-sulfur submerged sinkholes that resemble life on early Earth, may offer some answers. Herein, mats are dominated by motile filaments of purple-pigmented cyanobacteria capable of oxygenic and anoxygenic photosynthesis, and pigment-free chemosynthetic sulfur-oxidizing bacteria. We captured time-lapse images of diurnal vertical migration between phototactic cyanobacteria and chemotactic sulfur-oxidizing bacteria – dramatically turning the mat surface purple at dawn and white at dusk. Alternating waves of vertically migrating photosynthetic and chemosynthetic filaments rapidly tracked diurnally fluctuating light; observations corroborated with intact mats under simulated day-night conditions. Both types of filaments increased in surface coverage non-linearly, albeit at different rates. During their respective surface takeovers, maximum nightly rate of movement for white chemosynthetic filaments occurred an hour before that of purple cyanobacteria during the day. However, though slow to start at dawn, the cyanobacteria’s maximum rate of movement was double that of the chemosynthetic bacteria, leading to greater total coverage over the span of the day. Such synchronized diurnal “tango” might have been the largest daily mass movement of life during the long Archean and Proterozoic eras, when the biosphere was mostly benthic, and played a critical role in optimizing photosynthesis, chemosynthesis, carbon burial, and oxygenation. Further studies of extant microbial “mat worlds” will add to the expanding knowledge of Earth’s biodiversity and physiologies, and may aid our ongoing search for life in extraterrestrial waters.