The ultimate cause of plate tectonics is the movement of continents the mid-oceanic ridge the cooling of the earth the heating of the earth

The correct answer is - the movement of continents.

The plate tectonics are a result of the movement of the continents, or tectonic plates. This movement is caused by the high pressure and temperatures in the mantle layer, or better said, in its upper part, the astenosphere. Because of the high pressure and temperatures from bellow, the crustal part of the Earth cracks at some places, and it is moving slowly to a certain direction dependently from the push force from bellow. These cracks in the crust make the Earth's surface look like a puzzle, with multiple tectonic plates slowly moving around the planet.