Q:

Could we extract energy/heat from the mantle?

the question is if lava in the mantle of earth is so hot then could we extract this energy to produce heat?=
we would introduce some tubes that can stand temperatures of 10000 K or more then by difference of pressure the heat or lava would come up and then we can use this heat to produce energy

A:

Well this probably would be very inefficient and even if the tubes could sustain temperatures of 10,000 Kelvin no one could touch that tube and it would get real hot. Also for all that heat to reach the surface it would still take time. Also eventually those tubes would get so hot they might have some chemical reaction with the mantle and if the tube was able to sustain those high temperatures in the past it would not be able to do it after reacting with the lava. Furthermore the tube would experience wear and tear faster than ever. A much more efficient way is to send water down there which evaporates and then that water would not carry so much energy as to burn the surroundings but enough energy to do important things like power a city with the energy.

