Ours is an active planet. A constant flow of heat moves up toward the earth’s crust, generating tectonic plate movement, earthquakes, volcanoes, and mountain making. About a fifth of the earth’s internal heat is primordial, lingering from the planet’s formation 4.6 billion years ago. The balance is generated by ongoing radioactive decay of potassium, thorium, and uranium isotopes in the crust and mantle. The heat energy generated is about 100 billion times more than current world energy consumption. Geothermal energy—literally “earth heat”—creates underground reservoirs of steamy hot water.
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