Can we harness Earth's heat to power the planet?

It is already is. This is why Iceland's a producers of bananas, cecause it's a centre of geothermal activity. It's an area on the Earth's surface where heat from inside actually heats up things like water, so you get very hot geysers, hot rocks and areas of the earth. You can harness that heat, and in Iceland they use it to power their greenhouses for growing bananas. In other parts of the world as well there is geothermal heat being used to generate energy. In New Zealand, it's already used. The way you do it is you pump water down to where the rocks are hot enough and the water comes up at very high temperatures and very high pressure. You can then either send that water off as a direct distribution or you can pass it through a heat exchanger and then distribute that heat around people's houses, hospitals and places that need energy. It's great for bathing in too. However, this is only used where it's economical and the rocks are close enough to the surface.