main sources of heat in the earth?

Answer 1

Radioactive potassium, uranium and thorium are thought to be the three main sources of heat in the Earth's interior, aside from that generated by the formation of the planet. Together, the heat keeps the mantle actively churning and the core generating a protective magnetic field.
The heat within the core may also come from some of the iron becoming solid and joining the inner core, or perhaps it is generated by radioactivity, like the heat of the Earth's crust.

Answer 2

Radioactive decay of uranium, thorium and potassium. Uranium liberates 0.74 cal/(g yr), thorium 0.20 and potassium 0.000026. Since potassium is common compared to uranium or thorium, the total heat per gram of crust becomes: uranium, 2.2 microcalories per year, thorium 2.9 and potassium 0.9. Total heat is 10^20 calories per year (100,000,000,000,000,000,000 or 100 sextillion calories).

Answer 3

isn't the sun one?