eli5 Where does the earth’s core get the energy to generate heat from?

Question

The suns energy is from fusion, fine makes sense.

But the core is a hot spinning liquid metal generating tremendous amounts of heat. Why hasn’t it cooled down? How is it replenishing its energy?

In: Planetary Science

Answer 1

Most of the Earth’s energy to heat it’s core came from gravitational energy of its formation. Some of it probably came from that possible impact that formed the Moon. The interior of the earth will eventually cool, but on our best estimates the sun will be a problem long before that. The core is also warmed some by radioactive decay.