Plates move over the asthenoshpere, which is part of the mantle that has the property of plasticity. Its like a semi solid. Convection affects the plates movements. Convection is the transfer of energy in a fluid (liquid or gas), in which warmer fluid rises and cooler fluid sinks in a convection current. In the asthenosphere, the mobile rock (mobile from plasticity) moves in a circular motion. Heated rock closer to the core rises to the surface, spreads and begins to cool, then sinks back down again to be reheated and rise again.
