Answer:
Heat/temperature
Explanation:
"There are three main sources of heat in the deep earth: (1) heat from when the planet formed and accreted, which has not yet been lost; (2) frictional heating, caused by denser core material sinking to the center of the planet; and (3) heat from the decay of radioactive elements." These give the core and a few of the outer layers of the earth more and more heat.
