In Section 2, the author talks about the 3 different types of heat transfer: radiation, conduction, and convection. It also explains how the different types of heat transfer occur in the earth.
One type of heat transfer is radiation. Radiation is the transfer of energy through space, using electromagnetic waves. This type of heat transfer doesn’t require direct contact. An example of radiation is the sun giving light to earth.
Another type of heat transfer is called conduction. To transfer heat through conduction, heated particles in something transfers heat to the particles of another substance by touching.
The last type of heat transfer is convection. Convection transfers heat by using moving currents in gases or fluids. The sun heats up the equator the most. The warm air rises, but it cools down at a higher altitude, sinking. That creates a current, but it is just one example of convection currents. Convection currents are caused by the heating and cooling of the fluid, changes in density of the fluid, and the force of gravity.
Inside the earth, it is basically the same. The core is the hottest, so it conducts heat to the outer core. Then, the outer core uses conduction again to conduct heat to the mantle. In the mantle, there are convection currents. The hottest part of the mantle is near the outer core, so the hot rock there rises toward the crust. Then, it cools, and sinks back down again.