Earth gives off a relentless hum of countless notes completely imperceptible to the human ear, like a giant, exceptionally quiet symphony, but the origin of this sound remains a mystery.
unexpected powerful tunes have been discovered in this hum
The planet emanates a constant rumble far below the limits of human hearing, even when the ground isn't shaking from an earthquake.
discovered a decade ago, is one that only scientific instruments - seismometers - can detect
his murmur could originate from the churning ocean, or
In the past, the oscillations that researchers found made up this hum were "spheroidal"
oscillations have been discovered
that, oddly, are shaped roughly like rings
spheroidal oscillations might be caused by forces squeezing down on the planet - say, pressure from ocean or atmospheric waves - the twisting ring-like phenomena might be caused by forces shearing across the world's surface, from the oceans, atmosphere or possibly even the sun
clipped from: www.unexplained-mysteries.com 