Where does the Earth's heat come from?

Our planet's interior is still pretty much a mystery to scientists and all models of the inner Earth depend on indirect evidence. The widely accepted theory about the continuous flow of Earth's heat is linked with the radioactive decay of uranium, thorium, and potassium in Earth's crust and mantle.

The amount of this heat is enormous. The recent geological study that used temperature measurements from more than 20,000 boreholes around the world has found out that around 44 terawatts (44 trillion watts) of heat continually flows from Earth's interior into space.

The scientists believe that a radioactive decay supplies only around half of Earth's heat. Among other heat sources are primordial heat left over from the planet's formation and compression due to gravity.

The Japanese scientists have discovered that uranium 238 decay accounts for about eight terawatts of the Earth's heat, thorium 232 accounts for eight, and potassium 40 another four.

Earth has enough heat to create magnetic field and ensure constant movement of plate tectonics. This is so far the only certainty about Earth's heat.