Scientists Capture Mysterious Sounds Permanently Produced by Earth

For the first time, Earth’s eerie vibrating noise has been recorded from the bottom of the ocean by scientists, but they still don’t know exactly why our planet hums.

A team led by Martha Deen at the Paris Institute of Earth Physics carried out a pioneering experiment and recorded the Earth's hum from deep under the sea.

"The Earth's hum is the permanent free oscillations of the Earth recorded in the absence of earthquakes," scientists wrote in the study published in Geophysical Research Letters.

The sound with frequencies between 2.9 and 4.5 millihertz is inaudible to human ears — it's about 10,000 times below the limits of our hearing. However, from time to time people have reported hearing an unusual low-frequency noise. Scientists have been trying to capture this hum since 1959, but Japanese scientists only proved its existence in 1998.

The researchers of the Paris Institute of Earth Physics first gathered observation data from 57 seismometer stations collected during 11 months on the seafloor in the Indian Ocean east of Madagascar. After that, they painstakingly removed any sources of interference from identified sources, including the signals caused by ocean infragravity waves, seafloor currents and electronic glitches. What they had left was Earth's hum.

It still remains unclear what causes the hum. According to one suggestion, it can be caused by waves bashing against the sea floor across the planet or by the effect of atmospheric turbulence, but the latter could only explain part of the vibration's loudness, scientists noted.

Besides hoping to discover the origin of Earth's hum, the team believes their research could help map the planet's interior, which is usually done using seismic data from earthquakes. Because the hum is constant, geologists wouldn't need to wait for earthquakes for data.