No matter how closely you listen, you will not hear the Earth hum—but humming it is.
Far, far below the range of human hearing, waves of energy are coursing through the crust, causing the ground beneath your feet to rise and fall about three-millionths of an inch every few minutes. First detected by networks monitoring seismic activity in 1998, the tiny ripples were initially chalked up to the many small earthquakes that occur each day around the world. But studies over the past decade have proved that the hum is far too constant for that explanation.
