Thermal evolution of the Earth: the modes of mantle convection in the Precambrian

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Plate tectonics is a special class of mantle convection, being observed only on Earth among terrestrial planets in our solar system. It is responsible for a vast array of geological processes, from the generation of continental crust to the modulation of atmospheric composition. Yet, some fundamental questions about its history remain unresolved: when plate tectonics began on Earth and how it has evolved through time. This project aims to resolve the likely mode of mantle convection in the Precambrian (i.e., after the solidification of the putative magma ocean in the early Earth to the beginning of the Phanerozoic at 540 million years ago), by building a robust theoretical framework and exploring its implications for geological and geochemical observations. Reconstructing the evolutionary path of plate tectonics on Earth is one of the most fundamental geophysical problems, providing a global context for geological, geophysical, and geochemical processes, and the radius of the potential impact of this research would cover nearly all branches of solid Earth sciences. Expected research results should also find their applications in the physics and chemistry of terrestrial planets at large and are expected to become part of the theory of habitable planets. This project will provide support and training for a postdoctoral associate and a graduate student, as well as summer intern or thesis projects for undergraduates. The planned research has the following five major objectives: (1) Establishing a regime diagram of mantle convection as a function of internal Rayleigh number, the temperature dependency of viscosity, yielding criteria, and the internal heating ratio, so that we can estimate how the mode of convection has evolved in the past, (2) quantifying the relation between quasi-steady-state solutions and transient situations, in terms of the mode of convection and heat-flow scaling, so that we can analyze collectively different numerical approaches to the evolving mantle dynamics in a unifying fashion, (3) understanding 3-D effects on the mode of mantle convection on the basis of newly-developed scaling laws and published simulation results, (4) exploring the influence of the thermal evolution of the core on surface tectonics by a systematic investigation of coupled core-mantle evolution models, and (5) connecting internal mantle dynamics with surface observables, such as global sea level, plate velocity, and geomagnetic field strength, so that we can build falsifiable hypotheses for the evolution of mantle convection in the Precambrian.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.