If you turned off every video game system, car stereo, and TV on the planet, and if everyone held their breath and didn’t make a peep, there would still be a sound, though you couldn’t exactly hear it.
You may not know it, but the Earth is always emitting a low hum, which geophysicists call the free oscillation of the Earth.
In a recent study, geophysicists have measured Earth’s background hum on the ocean floor for the first time. That’s right, the Earth makes noises constantly, even when it’s not rumbling or cracking.
