Understanding Convection Currents
If you put a pot on a stove to boil some water, you will notice something interesting. The heat from the stove heats the water at the bottom of the pot. This water will rise to the top of the pot. You will see this in the form of bubbles rising to the top of the water. As the hotter water rises, colder water that was on at the top will descend (move down) to the bottom of the pot. This in turn will be heated and the process repeats itself. In this way a cycle is set up. Heat is moved with the water from the bottom of the pot to the top and back down again. This process is called convection. The water moves in currents.
If you imagine the stove as the Earth’s Core and the pot of water as the Mantle, you will understand what happens under the crust. The Core heats the Mantle. Heat rises up through the Mantle to the Transition Zone just under the crust. This causes the molten rock under the crust to move in convection currents. When this molten rock moves, it creates a drag effect under the Crust that actually pulls the Crust with it. This is how the plates of the Crust move. They are dragged by convection currents. If you throw an ice pop stick into the centre of a pot of boiling water, the stick will move to the edge of the pot (if you wish to try this at home, make sure you have supervision). The stick behaves just like the plates of the earth. As the convection currents move, so too do the plates.