Convection currents transfer heat from one place to another by mass motion of a fluid such as water, air or molten rock. The heat transfer function of convection currents drives the earth’s ocean currents, atmospheric weather and geology. Convection is different from conduction, which is a transfer of heat between substances in direct contact with each other.
First and second law of thermodynamics
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatra.html