Earth's oxygen and phosphorus cycle and the evolution of animal life

Abstract

The purpose of this study is to reconstruct an environmental context for the emergence and expansion of early animal life during the Middle Proterozoic (∼1.8–0.8 billion years ago). Specifically, we examined the spatially and temporally evolving Earth surface ocean oxygen (O2) concentration impacted by atmospheric partial pressure of oxygen (pO2) and phosphorus levels. We exploited a quantitative biogeochemical model - the Grid ENabled Integrated Earth system (cGENIE) model, which consists of a reduced physics 3-D ocean circulation model coupled to a 2-D energy-moisture balance model of the atmosphere and a dynamic-thermodynamic sea-ice model. Our results suggest a challenging evolutionary landscape for basal metazoan life characterized by spatiotemporal variation in surface ocean oxygen level and prevalent benthic anoxia even with surface ocean-atmosphere oxygen level sufficient to support basal biological activities. By studying the environmental variability presented during the evolutionary history of complex life on Earth, we are thus equipped with a valuable tool to examine the potential biotic complexity throughout the universe.