The late Neoproterozoic witnessed remarkable changes in almost all envelopes of the planet. The biosphere experienced one of its most fundamental evolutionary steps with the rise of complex life forms, which was accompanied by fluctuations in oceanic deep-water redox conditions, extreme climate modes, and major changes in the configuration of continents. In this context, links between biological innovation and environmental changes are usually implied, but we know little about the relative roles of environmental and biological factors, their effects and feedbacks involved in the late Neoproterozoic events leading to the ultimate oxygenation of the ocean-atmosphere system and dawn of biological complexity. We intend to fill these gaps by integrating information about the chemistry of the oceans, evolution of complex life, paleogeography and tectonics between the Cryogenian and the early Cambrian. For that we will integrate four sub-projects: (1) high resolution sedimentological and geochronological work on four basins in Brazil and Africa covering the time interval of interest, (2) detailed investigation of the paleontological record on these four successions, and examination of the physiology, ecology and developmental behaviour of early metazoans to test hypothesized connections between changes in ocean redox, nutrients and the evolution of life, (3) a multi-proxy geochemical study of the four sedimentary successions, (4) reconstruction of the still poorly resolved late Neoproterozoic paleogeography and topography, and numerical modeling of the climate-ocean system in a better constrained paleogeographic context. The overall objective of the proposal is to better understand the feedbacks between life, environment and tectonics at the advent of the modern Earth, in particular climate and ocean geochemical change at the origin of the metazoan ecosystem.