Plates and Their Movements
The movements of plates has not gone unnoticed, and although the changes seem happen at almost glacial speeds, in the long run the tiny movements in the earth's crust add up to some huge differences in the future.
Convection currents in the mantle push upwards then run laterally along the undersides of plates in the hydrosphere. These currents are caused by magma (molten rock heaten by the Earth's core) that rises to the surface through the mantle. The force of this spreading motion means that some
of the crust moves along with the currrent, as if being dragged and the gap that is after this spreading is filled with the magma which is rapidly cooled thus turning into more crust.
The spreading motion caused by the expanding of the crust forces entire plates to shift which means that somewhere, the older crust must go somewhere. The answer to that comes in the form of convergent boundaries. At these boundaries, the older crust is either pushed upwards to form mountains or pushed back down under the other plate. Crust that sinks back into the mantle is melted down into molten rock.