STROMATOLITES: AN EARLY PHOTOTROPH SURVIVAL STRATEGY WHICH LATER HELPED DRIVE THE OXIDATION OF THE EARTH’S OCEANS NECESSARY FOR THE GREAT OXIDATION EVENT

The Archean eon spans 1 billion years, where geobiological evolution, shifting tectonic regimes, and orbital dynamics ultimately led to the Great Oxidation Event (GOE) at ~2450 Ma – arguably the most important step towards the formation of the modern bio and geospheres. We combine evidence from geological (tectonics, craton and crustal formation) geochemical (oxidation proxies, sedimentary manganese concentration, C isotopes), microbiological (phototrophy, nitrogen fixation, sulfur metabolism, cyanobacterial evolution), and orbital mechanics (moon proximity effects on day length and tides) to build a contextual framework for the co-evolution of life and the Earth’s surface. Within this context, we made measurements of stromatolite volumes from units formed between 3.5 and 2.5 Ga across North America, Australia, Africa, India, Eurasia, and South America, which exhibit a one to four order of magnitude increase after ~ 3 Ga. Measured carbon fixation rates of modern chemotrophic, anoxygenic, and oxygenic microbial community analogs are consistent with metabolic limits to stromatolite growth. Our investigation suggests: 1) the effective combination of oxygenic photosynthesis with nitrogen fixation by cyanobacteria by ~3 Ga represents a key breakthrough necessary to help drive oxidation of the Earth’s surface, supported by molecular clock calculations, increased manganese concentrations in sedimentary rocks, shifts in carbon isotope values, and multiple redox proxies (Cr, Fe, Mo, U); 2) the development of stromatolitic structures and the evolution of oxygenic photosynthesis was likely a response to tidal strength and frequency; and 3) the onset of modern plate tectonics provided stable shallow shelf environments that were ideal for the proliferation of oxygenic phototrophic microbial communities to drive oxidation of the surface ocean necessary to initiate the GOE.