Convection currents occur in the Earth's geosphere, atmosphere and hydrosphere when heat is transferred from one place to another. Heat energy moves from hot places to cold places during convection.
Heat generated from decaying elements in the Earth's interior creates magma, or liquid rock. Convection currents move heated magma from within the Earth's mantle closer to the surface at tectonic plate boundaries. This convection pulls plates apart at the surface.
In the atmosphere and hydrosphere, heat comes from the sun. Convection currents in the air are driven by unequal heating that create high and low pressure systems. Air travels up and down through the atmosphere as it's heated near the surface and then cools higher up.