i assume you mean "heater core". this is a really small radiator usually located behind the dashboard of your car. a fan blows across it when you turn the heat on. this radiator can leak eventually,...
Initially the earth heated up using energy released buy gravitational collapse, and while this energy completely melted the planet, this heat would have all been lost by now as the Earth is 4.6...
The inner core of the Earth is believed to be composed of iron and nickel, with a dash of other heavy metals. Several of these are radioactive, and this fission creates heat. Studying seismic waves...