Correct Answer: Radiogenic heat and primordial heat

Solution : The correct option is Radiogenic heat and primordial heat .

The planet's internal heat engine is fueled by heat from radioactive material decay and heat left over from Earth's birth. Radioactive atoms have energy that spontaneously escapes as gamma rays or very energetic subatomic particles. The radiogenic heat created by the radioactive decay of isotopes in the mantle and crust and the primordial heat remaining from Earth's origin are the two main sources of the about equal amounts of heat that flow from the planet's interior to its surface.