Plate Tectonics

Plate tectonics is the root concept underpinning our current knowledge of how Earth's internal dynamics are linked to geologic deformation at the surface. Since the discovery of plate tectonics in the 1960s, geoscientists have developed a first-order understanding of a plate system in which the Earth's surface is broken into about a dozen mostly rigid tectonic plates that move relative to each other at speeds of a few centimeter per year. The boundaries of these plates accommodate diverging, converging, and lateral motions, and are associated with surface features such as rift zones, mountain belts, faults, earthquakes, and volcanoes. The motions of the plates can be detected geodetically, described kinematically, and reconstructed back in time. This descriptive understanding of Earth's surface deformation is now recognized as the surface expression of a larger, dynamic framework of mantle convection. Gravity acting on density variations within Earth's interior generates broad-scale flow of the mantle, which mainly drives, but can also resist, the horizontal plate motions at the surface. Within this system, oceanic plates originate from and are recycled back into the mantle, forming a dynamic cycle captured by the recently described “ocean-plate tectonics” concept. This intimate relationship between surface and internal dynamics appears to be unique to the Earth, as it is clearly different from the modes of mantle convection inferred for other rocky planetary bodies within our solar system. Earth's unique interplay between its interior and surface shapes our planet's morphology and recycles its volatiles to produce the lively and life-bearing planet that Earth has become. How ocean-plate tectonics started, how it has repeatedly opened and closed ocean basins, assembled and dispersed supercontinents, and initiated and terminated fault systems, and how it continues to operate today are still major open questions. New techniques for studying Earth's interior dynamics, new possibilities for comparing Earth to other freshly understood or recently detected planetary bodies, and new unifying concepts like ocean-plate tectonics bode well for future resolution of the remaining mysteries surrounding plate tectonics today.