A solid core which is maintained solid due to the immense pressure it is under, consisting of iron and nuclear material which is decaying to produce the heat necessary to maintain a liquid core. as the liquid core heats, it rises to the surface, where it cools. Then dropping back towards the earth's core, where it is re heated and rised again, making a convetion current. this constant current moves the plates.This is happening in all directions by the way.
Explain how this can happen on a flat earth