Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core.
R. Feynman once remarked that we know more about the interior of the sun than about the interior of the Earth. Hence, we don't know much. One result of the ignorance is our inability to understand and predict earthquakes and volcanic eruptions.
Very few science fiction authors dared to go to the center of the Earth. These few are: 1) Jules Verne, "Journey to the Center of the Earth", 2) Vladimir Obruchev, "Plutonia". Judging from these science-fiction works, we really know very little about the Earth beneath us.We have already harnessed the energy of the earth beneath us to heat houses and produce electricity. This must be developed. See "Geothermal energy" on Internet.