Well, hello there, enormous quantities of heat that's just beneath our feet and could potentially be tapped to provide enormous amounts of base-load electricity! Where'd YOU come from? The birth of the planet, you say? No sh*t!
Using this gigantic underground, water-filled neutrino detector, scientists have finally gotten a better idea of exactly where the Earth's heat comes from:
Turns out only half of that heat comes from radioactive decay deep within the planet (which was previously our best guess). The other half may actually be leftover heat from when the Earth and its buddies were formed.
It's like Earth is a burning hot ember removed from the fire that forged it, slowly radiating its heat into the vast, cold reaches of outer space. To the tune of 44 trillion watts of heat energy, all day, every day.
When we drill into the earth's surface to tap that heat energy for geothermal power, we're siphoning off a teeny tiny bit of that heat. But don't worry, it's so vast that our comparatively minuscule energy needs can't ever exhaust it. Planet-crafting quantities of thermal energy do not mess around.