Surprisingly it's about 50/50 radioactive decay and heat left over from the forming of the solar system: https://en.m.wikipedia.org/wiki/Earth%27s_energy_budget

Surprisingly it's about 50/50 radioactive decay and heat left over from the forming of the solar system: https://en.m.wikipedia.org/wiki/Earth%27s_energy_budget#Earth's_internal_heat_sources_and_other_small_effects https://en.m.wikipedia.org/wiki/Earth%27s_energy_budget#Eart...