The mantle is present between the earth's crust and the core. It is not a static layer. The upper part of the mantle is called the asthenosphere which changes its shape with temperature and pressure. It is not a rigid layer. Any changes in the inner layer of the mantle cause the movements in asthenosphere plates. This is called the plasticity of the mantle. The convection is a process, where high temperature causes the movement of atoms. The atoms move from high-temperature region to the low-temperature region and thus a cyclic movement happens in the inner mantle. This causes the changes in the plates location of the upper mantle.
