Conduction
Convection
Radiation
Modeling Earth Systems

Earth is a heat engine. Its interior as well as its exterior are environments controlled by the flow of heat from hot to cold reservoirs. This is heat transfer. The earth's mantle and the atmosphere have in common a process of heat flow and mass exchange generically known as thermal convection. In the oceans and in the core convection is driven by compositional and density differences more than by heat.

Conduction, Convection and Radiation

In general, heat may be gained or lost by a substance by any one of three mechanisms: conduction, radiation and convection. Conduction warms your hands as you grab a mug filled with hot coffee, and your face is warmed up on a cool sunny day by radiation from the Sun. Convection can be easily observed as the bulk motion of water being heated in a kitchen pan. The Earth interior is very hot (up to 6,000 degrees K at the center of the inner core). Outer space is very cold, down to a few degrees K (that is, above absolute zero). The temperature difference means that heat from the Earth's interior must flow outwards, as our intuition tells us that heat moves spontaneously from a hot to a cold place. Thus, internal heat from the core, as well as heat being continuously generated in the crust and the mantle by the radioactive decay of uranium, thorium and potassium must move out.

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