 Earth 's internal heat comes from a combination of residual heat from planetary accretion ( about 20 % ) and heat produced through radioactive decay ( 80 % ) . The major heat @-@ producing isotopes within Earth are potassium @-@ 40 , uranium @-@ 238 , uranium @-@ 235 , and thorium @-@ 232 . At the center , the temperature may be up to 6 @,@ 000 ° C ( 10 @,@ 830 ° F ) , and the pressure could reach 360 GPa . Because much of the heat is provided by radioactive decay , scientists postulate that early in Earth 's history , before isotopes with short half @-@ lives had been depleted , Earth 's heat production would have been much higher . This extra heat production , twice present @-@ day at approximately 3 Ga , would have increased temperature gradients with radius , increasing the rates of mantle convection and plate tectonics , and allowing the production of uncommon igneous rocks such as komatiites that are rarely formed today . 
