The diversification and ecological rise of marine eukaryotes is an impactful evolutionary event that transformed the Earth system. When did it occur? What were the driving forces? What were its impacts on the Earth system? Increasing paleontological and geochemical evidence indicates that the ecological expansion of marine eukaryotes occurred in the Tonian Period, earlier than previously thought. Further, emerging geochemical data indicate that increasing availability of marine nutrients (particularly phosphate and nitrate) may have enabled the ecological rise of photosynthetic eukaryotes, which in turn opened ecological opportunities for the diversification of eukaryotes overall. The transition from a prokaryote-dominated to a eukaryote-dominated marine ecosystem, particularly in terms of export bioproduction and global carbon cycles, had profound impact on the Earth system and in the long run may have contributed to snowball Earth glaciations in the following Cryogenian Period.