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

Side note/question — How much energy input to the earth’s heat comes from gravitational flexing from the moon’s tidal interactions? Some sources I’ve seen claim terrain rise of 2 meters or more as the tidal bulges move with the moon alignment. The friction from this has led to the moon’s tidal lock, and moving further out in orbit. How much of this energy budget goes into the earth as heat?