No, the heat is not already there. The heat comes in and goes out; the heat energy initially in the crust decays away exponentially with time and has no effect on the steady stage temperature gradient.

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lxgr 2 days ago | parent [-]

What do you mean? It's already in the core and gradually reaches us through the crust. What's your point/distinction here, exactly?

	▲	pfdietz 2 days ago \| parent [-]
		It was not initially in the rocks that we are tapping for geothermal energy, which would be a few kilometers. I wasn't talking about the Earth as a whole. Remember, this is about why so much more thickness is needed for the rocks for ordinary geothermal energy systems, vs. artificial geothermal.