How has the earth's core stayed so hot for so long? When will it cool down?
Having stayed so hot for millions of years, it should take billions of years to cool down, at the present rate of releasing heat up to the surface, through volcanoes and similar venting.
Let it be hot inside. .Earthians are really fortunate.
In contrast, the star Sun's core energy is transported by radiation, through radiation zone, and then by convection (by rolling motion) through convection zone, onto surface. .