The upper 10 kilometers of the Earth’s crust contains vast geothermal reserves, essentially awaiting human energy consumption to begin to tap into its unstinting power output—which itself yields no greenhouse gasses. And yet, geothermal sources currently produce only three-tenths of one percent of the world’s electricity. This promising energy source has long been limited by the extraordinary challenges of drilling holes that are deep enough to access the intense heat below the Earth’s surface.N...