<human>:  I've been trying to read up on the continental drift theory, and I'd like to know what other theories of plate tectonics exist?
<bot>: Other common theories of plate tectonics include sea-floor spreading, which postulates that the ocean floor is constantly being created and expanded as new crust is formed at mid-ocean ridges and destroyed by subduction at ocean trenches; mantle convection, the process by which heat is transferred from the Earth's interior to its surface; and lithospheric plates, which explain how different sections of the Earth's crust move and interact.