Is the Earth Humming to Us?

finally recorded it. In the nineteenth century, geologists began to suspect that the Earth might be producing a constant hum, one which rings out even in the absence of earthquakes and seismic events. They also reasoned that the noise must be too quiet for our human ear drums to hear. The official name for this drone is permanent free oscillations.

Until somewhat recently, its existence was only theoretical. A team led by seismologist Hugo Benioff did try to detect the signal in ninety nine, but their efforts failed because the time science did not yet possess any instruments that were sensitive enough to pick up the hum. Theory became fact with the advance of technology in scientists at the Showa Station, a Japanese research base in eastern Antarctica. We're finally able

to prove that permanent free oscillations really do exist. The good news was announced a year later when the show A team published their findings. Since then, numerous other teams have observed the same noise. Now, for the first time ever, the Earth's ham has been recorded using seizeman equipment on the ocean floor. This is a big deal because every previous study which has documented the noise did so with land based instruments. The achievement was a hard won prize

for Martha Dean and her team. She's a geophysicist with the Paris Institute of Earth Physics. Under her leadership, the international team reviewed data collected over an eleven month period from fifty seven sizemometer stations on the floor of the Indian Ocean, and that was just the first step. Next, the researchers eliminated all forms of audio interference such as water currents and technical glitches from the recordings made at two of the stations. With the deletion of this extra noise,

Dean and her colleagues could finally isolate the hum. They were looking for. Why was it so important to record the oscillations with submerged seismometers. As Dean told us in an email, these instruments will broaden our perspective in a way that terrestrial tools never could. She said, ocean bottom sizedmometers can cover much larger areas than land based ones. For the ocean covers seventy of our planet. She added that we can better understand the phenomena by studying the

HUM signal at places far from land or islands. Maybe one day we'll even be able to pinpoint its source. You see, nobody knows exactly how the HUM is being made. A few different hypotheses have been put forth. Some geophysicists think gets generated by the ceaseless pounding of ocean waves onto continental slopes. Others believe that it could be the

product of atmospheric turbulence and global wind patterns. But if that second explanation is true, we'd expect the rumblings amplitude, that is, its loudness, to vary from season to season. Previous studies have claimed that this is happening, yet the new research says otherwise. Dean's group confirmed that the hums pitch rises and falls, with its maximum volume hitting a frequency of four point five milliherts. That's about ten thousand

times softer than the faintest noises our ears can detect. However, according to the team's findings that amplitude changes don't correlate with seasonality. Thus, Dean and her colleagues argue that atmospheric issues alone cannot account for the existence of these permanent free oscillations. They also think that their research could open the door for future research on the Earth's interior. Geologists use a process called tomography to map out the inside

of our world. Think of it as a large scale m r I scan. Dean explains that scientists invert the recordings of seismic waves to decipher the makeup of various layers and structures within the planet. Going forward, ocean bottom sizedmometers like those used in her recent study should give tomographers more data to work with. Hopefully we'll soon have a better idea of what lies beneath our feet. Today's episode was written by Mark Bancini and produced by Tyler Clang.

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