Earth internal heat

[Bucyrus]

Why is the earth hot inside?

[Azalian]

Radioactivity and the remnants of the heat from earths initial formation.

[gen2]

Some heat is also generated through gravitational 'friction' as the Earth interacts with the sun and the moon. The cost of this heat is a slowing of the Earth's rotation.

[Robb Phoenix]

Reasons:

1.
5-10%-- the heat left over from when gravity first condensed a planet from the cloud of hot gases and particles in pre-Earth space. As the molten ball cooled, some 4 billion -years ago, the outside hardened and formed a crust. The mantle is still cooling down.

2.
5-10%--gravitational heat-- In a gravitational sorting process called differentiation, the denser, heavier parts were drawn to the center, and the less dense areas were displaced outwards. The friction created by this process generated considerable heat, which, like the original heat, still has not fully dissipated.
3.
--latent heat-The inner core is becoming larger by about a centimeter every thousand years. The heat released by this expansion is seeping into the mantle.
4.
up to 90 percent--Radioactivity --the decaying of radioactive isotopes like Potassium 40, Uranium 238, 235, and Thorium 232 contained within the mantle. These isotopes radiate heat as they shed excess energy and move toward stability.