I propose a hypothesis for the origin of subduction on early Earth that is directly coupled with mantle upwelling and the formation of mafic crust. The hypothesis invokes spatial and temporal overlap of both endogenic and exogenic processes, broad quasi-cylindrical mantle upwelling and large bolide impact, respectively, leading to subduction and spreading, two signature processes of modern plate tectonics. The spatial and temporal intersection of these processes could have occurred variably across early Earth, and thus subduction could have begun at different locations and times globally. The hypothesis postulates that the ability of a terrestrial planet to evolve plate tectonics results from a balance between the strength of its lithosphere and the size bolide it can attract and survive; both factors, to a first order, are a function of planet size.

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