Our blue planet spins suspended in outer space—and it hums, too. European researchers say the Earth's incessant hum originates from the bottom of the ocean. This study, published in the journal Geophysical Research Letters in November, gleans material from ocean-bottom seismometer stations, contrasting with previous data from vibration tools based on land. "It's like taking a piano and slamming all the keys at the same time," says Spahr Webb of Columbia University's Earth Institute, who was not associated with the study. "Except they're not nice harmonics. They're oddball frequencies." Humming by the Numbers The planet's hum has tickled scientists' minds since 1959, but definitive research was not completed on the topic until 1998. This current paper is the first to document the rumble from the bottom of the ocean. The researchers, spread out across earth science institutes in Paris, Stuttgart, and Oxford, U.K., combed through 11-months' worth of seismometer records covering a patch of more than 1,200 square miles on the Indian Ocean floor east of Madagascar. From that data, gathered from 2012 and 2013, they homed in on two stations with high quality data and sliced out any interfering sounds from loud waves and electronic glitches. Behold: the native sound of the Earth.
Read More: National Geographic