Scientists have discovered a new dimension to the sub-aural sound emanating from our planet’s crust, dubbed “Earth’s hum.” Researchers have known about the hum, detectable only by seismometers, for a decade, though its ultimate cause is unclear. They expected to find hidden oscillations, but the amplitude of the new “ring-like waves” dwarfed expectations, LiveScience reports.
The hum is caused by rock in the Earth’s crust moving almost imperceptibly against itself, but what makes it move continues to puzzle scientists. While the older waves, described as “spheroidal,” might be caused by oceanic or atmospheric forces pressing down on the planet, the new circular waves could be the result of shearing forces caused by the ocean, the atmosphere, or even the sun. (Read more science stories.)