At the beginning of the Proterozoic Eon (2500 million years ago), the atmosphere virtually lacked oxygen and only simple micro-organisms inhabited the oceans. By the close of the Proterozoic (542 million years ago), the atmosphere and oceans contained sufficient oxygen to support animals and complex, tiered ecosystems. What drove this extraordinary transition on Earth’s surface remains speculative, but Earth’s evolving tectonic geography likely played a central role through its regulation of global climate, weathering of the continents, and nutrient fluxes into the oceans. This session aims to highlight the interaction of solid earth processes with the evolution of the atmosphere, hydrosphere and biosphere during this critical time. This session is sponsored by IGCP648.