Asked by: Riley Brightwell, Cornwall
Beneath us all is a seething cauldron of rock, wrapped round an iron-nickel core at temperatures similar to the surface of the Sun. Most of the heat comes from radioactive decay of elements like uranium in the surrounding mantle.
As this process will continue for billions of years yet, the Earth is likely to have been destroyed by the death of the Sun before it can solidify.
Robert is a science writer and visiting professor of science at Aston University.