See explanation below.
Work Step by Step
The evidence actually says all the earth's heating takes place in the mantle and crust, not the core. All models of the inner Earth depend on indirect evidence. Leading models of the kind known as bulk silicate Earth (BSE) assume that the mantle and crust contain only lithophiles (“rock-loving” elements) and the core contains only siderophiles (elements that “like to be with iron”). Thus all the heat from radioactive decay comes from the crust and mantle – about eight terawatts from uranium 238 (238U), another eight terawatts from thorium 232 (232Th), and four terawatts from potassium 40 (40K) So the heating from 2.89x10152.89x1015 kg of uranium, thorium, and potassium isn't in the core but it surrounds the core. The earth generates 20–29 (varies by source) terawatts from radioactive decay of heavy metals in the core and will be generating heat for over 90 billion years. There are a lot of different elements in the core brought on by a period of material differentiation within the crust and the mantle. The heavy metals migrated to the core when the earth was re-liquefied shortly after its formation and during the creation of the moon from a planet-sized collision.