Hadean geodynamics and the nature of early continental crust

Reconstructing Earth history during the Hadean defies the traditional rock-based approach in geology. Given the extremely limited locality of Hadean zircons, some indirect approach needs to be employed to gain a global perspective on the Hadean Earth. In this review, two promising approaches are considered jointly. One is to better constrain the evolution of continental crust, which helps to define the global tectonic environment because generating a massive amount of felsic continental crust is difficult without plate tectonics. The other is to better understand the solidification of a putative magma ocean and its consequences, as the end of magma ocean solidification marks the beginning of subsolidus mantle convection. On the basis of recent developments in these two subjects, along with geodynamical consideration, a new perspective for early Earth evolution is presented, which starts with rapid plate tectonics made possible by a chemically heterogeneous mantle and gradually shifts to a more modern-style plate tectonics with a homogeneous mantle. The theoretical and observational stance of this new hypothesis is discussed in conjunction with a critical review of existing proposals for early Earth dynamics, such as stagnant lid convection, sagduction, episodic and intermittent subduction, and heat pipe. One unique feature of the new hypothesis is its potential to explain the evolution of nearly all components in the Earth system, including the atmosphere, the oceans, the crust, the mantle, and the core, in a geodynamically sensible manner.