Why do tectonic plates move?

Earth’s outer shell is broken into rigid tectonic plates that rest on a hotter, weaker layer called the asthenosphere. Heat from the core and mantle creates slow convection, and the sinking of cold, dense oceanic lithosphere at subduction zones helps pull plates along. This motion is extremely gradual but powerful over geologic time, with many plates moving about 2 to 10 centimeters per year. The theory of plate tectonics became widely accepted in the 1960s, building on earlier ideas from Alfred Wegener’s 1912 continental drift proposal. It explains earthquakes, volcanoes, mountain building, and the opening and closing of oceans.