What is the heat source in the Earth’s core?

Question

I understand that the Earth’s core is full of very hot liquid rock, but why is it hot and why does it stay hot?

What is the heat source?

In: Planetary Science

Answer 1

It started off as just the heat of rocks colliding together during the Earth’s formation.

Since they were flying through space, they had kinetic energy and gravitational potential energy with each other. When they collide and deform each other, they release that energy as heat.

That alone only gives the Earth enough heat to last a few million years before it cools to what we have now. The decay of radioactive elements gives the Earth enough heat to keep it warm enough to reach its current point after 4.6 billion years.