Why are earth's continental plates continually in motion?

the push from earth's ocean currents produces plate movement.

the continental plates do move, but not continually.

plates float on the liquid mantle located below the crust.

the earth itself is in motion as it revolves around the sun.

Plates float on the liquid mantle located below the crust.

Explanation:

    The “Continental Displacement Theory” or “Continental Drift” was created by the German geologist and meteorologist Alfred Wegener (1880-1930) in an effort to clarify the fact that the geomorphological conformation of some continents is appropriate, leading him to believe that the continents they were already united and parted, drifting slowly over the ocean basins.

    Thus the earth's crust, made up of tectonic plates, is drifting over the mantle of molten rock, which displaces those plates with the force of magnetism from within the earth.