Thanks to humans, the Earth is a pretty noisy place. We’re loud creatures — certainly more so than any other animal ever to walk the planet — and we’re even louder when we get together with other humans. But the Earth isn’t totally silent, even without noisy animals all over its surface, and scientists are trying to figure out why that is. For the very first time, researchers have captured an underwater recording of a mysterious noise that Earth has apparently be producing for eons, and they still aren’t sure why.
The sound which the planet produces is a low, steady, unceasing hum. Scientists have been attempting to record and explain the odd noise as far back as the late 1950s, with little concrete data to suggest its source. Now, new research published in Geophysical Research Letters is attempting to explain why it happens, and scientists think it might have something to do with the ocean.
“The Earth’s hum is the permanent free oscillations of the Earth recorded in the absence of earthquakes,” the research paper explains. The existence of the sound, which had gone for decades without being confirmed by additional research, was finally supported by Japanese scientists in 1998.
This newest study is the first to actually record the sound from deep beneath the ocean’s waves. By recording ambient sound within the ocean and then using robust noise cancelling techniques to strip away the sound of the ocean itself, scientists were left with only the sound. They were able to confirm that the noise is completely continuous and, over nearly a year of observation, did not vary significantly.
But what actually causes it? Well, the jury on that is still out, but various theories have been proposed. One of the more plausible explanations is that the Earth’s hum is actually acoustic resonance. Acoustic resonance, which is the process by which objects of similar natural frequency will vibrate in sync with each other even if they’re not directly touching, could cause the Earth to produce a continuous vibration, some scientists believe, but others aren’t so sure.
Further research is most certainly warranted, and even if the cause of the hum turns out to be something rather mundane, it could still help give us a rare glimpse at the inner workings of our planet.