Re-inventing the planet: the Neoproterozoic revolution in oxygenation, biogeochemistry and biological complexity

The Earth is a truly remarkable planet. In addition to the physical processes driving plate tectonics, climate and ocean-atmospheric exchange, it supports an extraordinary diversity of living organisms, from microbes to mammals and everything in between. Such wasn't always the case, however, and it is clear that both the planet and its biosphere have evolved - indeed, co-evolved - over deep time. In the past two billion years, by far the most fundamental shift in this co-evolutionary process occurred during the Neoproterozoic (1000 to 542 million years ago), a planetary revolution that culminated in the modern Earth system. The Neoproterozoic begins with a biosphere populated almost exclusively by microbes, and ends in the midst of its greatest ever evolutionary radiation - including the diverse macroscopic and biomineralizing organisms that define the modern biosphere. At the same time, it witnessed the greatest climatic and biogeochemical perturbations that the planet has ever experienced, alongside major palaeogeographic reconfigurations and a deep ocean that is becoming oxygenated for the first time. There is no question that these phenomena are broadly interlinked, but the tangle of causes, consequences and co-evolutionary feedbacks has yet to be convincingly teased apart. In order to reconstruct the Neoproterozoic revolution, we propose a multidisciplinary programme of research that will capture its evolving geochemical and biological signatures in unprecedented detail. Most significantly, these collated data will be assessed and modeled in the context of a co-evolving Earth system, whereby developments in one compartment potentially facilitate and escalate those in another, sometimes to the extent of deriving entirely novel phenomena and co-evolutionary opportunities. Our approach will be guided by three general hypotheses, testable against accruing data and theory: H1) that the enhanced weathering associated with land-dwelling eukaryotes was initiated in the early Neoproterozoic leading to major environmental change, including extreme glaciations and stepwise increase(s) in atmospheric oxygen concentration; H2) that major environmental changes in the mid Neoproterozoic triggered the emergence of animals; and H3) that the late Neoproterozoic-Cambrian radiations of animals and biomineralization were themselves responsible for much of the accompanying biogeochemical perturbation. Primary data for this project will be assembled from field studies of key geological sections in the UK and North China, along with contributed sample sets from Namibia, Spitsbergen and various archived collections. Together, these offer close to comprehensive coverage of the Neoproterozoic - not least, spectacular new surfaces of Ediacaran macrofossils from Charnwood Forest. Collected samples will be analysed to assess associated weathering and climate (Sr, C, O and S isotopes), oceanic redox conditions (Fe speciation and trace metals), nutrient dynamics (P speciation and trace metals) and biological constituents (microfossils, macrofossils and biomarker molecules). These data will be integrated and interrogated through the development of heuristic, spatial and evolutionary models. Beyond its integrative approach, the strength of this proposal lies in the diversity of the contributing researchers. Alongside our own expertise in biogeochemistry, palaeobiology and Earth system modelling, we are very pleased to have attracted world-class project partners in Neoproterozoic stratigraphy, geochronology and biomarker analysis. Further insight will come from our contingent of two PDRAs and three PhD students working across the range of topics and linked via a schedule of regular team meetings. Taken together, we anticipate a fundamentally improved understanding of the Neoproterozoic Earth system and the co-evolutionary interplay between the biosphere and planet.