Did you know that the earth is constantly humming? The sound is far below the human hearing threshold, but European scientists have determined that the Earth’s hum is coming from the ocean floor. The team used ocean-bottom seismometer stations to provide a clearer picture of the phenomenon than ever before. “It’s like taking a piano and slamming all the keys at the same time,” said Spahr Webb of Columbia University’s Earth Institute, according to National Geographic. “Except they’re not nice harmonics. They’re oddball frequencies.”

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The researchers, who hail from various earth science institutes across Europe, searched through seismometer records gathered from an area that stretches more than 1,200 square miles to the east of Madagascar in the Indian Ocean. Using this data, the team determined two high-quality seismometer stations from which it extracted the sound of a humming Earth. However, at 2.9 to 4.5 millihertz, the vibrations are nearly 10,000 times lower than the frequencies that humans can detect. From this data, scientists were able to determine that the loudness of the hum does not change over time, contradicting previous studies that documented a range of amplitude for the sound.

Related: Everything we know about the Earth’s mantle is completely wrong

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While scientists have been aware of the Earth’s humming since 1959, with more definitive research emerging in 1998, the source of the sounds remains a mystery. A better understanding Earth’s humming may prove invaluable to creating a more comprehensive map of Earth’s interior, which is usually only able to be studied during earthquakes. Although the recent study has not definitely determined the source and nature of Earth’s humming, it has clarified the phenomenon and offered opportunities for further research. “To better understand where the signal comes from, we believe that observing oscillations from the ocean bottom can help,” said study co-author Martha Deen, according to National Geographic. The most recent study credits atmospheric turbulence and ocean waves with causing the sounds, though this is far from conclusive.

Via National Geographic

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