Why is the core of the earth molten?

Why does the solid part of earth (crust) float over the liquid part of the earth (core) ?

• We know solid is denser than liquid, and that the denser materials settle at the bottom, why then does the crust not settle into the interior of the earth and the liquid core come and float on top?

• Answer:

  The solid crusty part is made from lighter granite rock - floating on a more dense basalt-like semi-molten rock.