Global scale numerical models of the emergence of plate tectonics and complex life on Earth

It is increasingly considered that the modern episode of plate tectonics began in the Neoproterozoic following a period of reduced activity known as the boring billion, when the Earth may have been in a less dynamic single lid mode (Sobolev & Brown, 2019; Stern, 2007). The Neoproterozoic was also a time of dramatic change in other Earth systems: higher oxygen levels, the Cryogenian glaciations, and finally the emergence and rapid diversification of multicellular life of the Cambrian explosion. The study of the transition to modern plate tectonics in the Neoproterozoic is therefore central to the emerging multidisciplinary field of Biogeodynamics, the study of coupling between geodynamic processes, climactic processes, and the evolution of life (Gerya et al., 2020). It is typically considered that modern plate tectonics is a result of the secular cooling of the mantle enabling local episodes of subduction to become more widespread and stable (Bercovici & Ricard, 2014). Sobolev and Brown (2019) argue that major erosion and sedimentation events, such as the Cryogenian glaciations, were important controls on Earths tectonic style. The presence of hydrated sediments in active subduction zones enhances their stability through lubrication, thus the Cryogenian glaciations may have assisted the activation of plate tectonics following the boring billion (Stern, 2007). The transition to modern plate tectonics is a global phenomenon operating on a timescale of hundreds of millions of years needed to develop/activate the global plate mosaic (Bercovici & Ricard, 2014). To model the transition numerically, we propose to combine global 3D models of mantle convection with a free surface using StagYY (Tackley, 2008) with simplified models of erosion and sedimentation, and a parameterised description of margin strength which may be modified by subduction zone lubrication and sediment loading. The aim is to determine through modelling the conditions and timescales required to activate a plate tectonic regime from a single lid (Stern, 2007). The results of these global models, particularly models of global topographic evolution, may also be used in conjunction with climate models and models of biological evolution to investigate the ability of different global tectonic regimes to sustain and diversify complex life.