6 strange sounds from Earth

#1 Skyquakes

It has been suggested that skyquakes could be the result of gas escaping from underwater vents

Strange booms in the upper atmosphere can make it seem like an extraterrestrial life form is about to descend upon humankind. However, these weird noises aren’t the result of little green aliens – they are in fact ‘skyquakes’, and they have been heard for centuries. Multiple explanations have been suggested for this phenomenon, from military action to meteorites, the release of natural gas to mini avalanches. There is, however, no definitive explanation, meaning the cannon sounds of a skyquake are still a mystery.

#2 Dawn Chorus

Batfish are just one of many fish species that make sounds underwater

At the breaking of dawn it’s common to hear the chirping and tweeting of songbirds, but what about the bass and pops of fish? The songs of marine life are often reserved for marine mammal solo singers, but over an 18-month study at Port Hedland in Western Australia it was revealed that several fish choruses are harmonising at dust and dawn. From the foghorn sounds of black jewfish to the buzzing tones of terapontidae, at sunrise and sundown the sea is awash with marine melodies.

#3 Earth’s Hum

Many machines come with that expectant humming sound, which is often proof they are working. The Earth is no different, but with a lack of a motor to investigate, scientists have been searching for the sound’s origins. Last year, a study published by researchers from the Paris Institute of Global Physics recorded the relentless planetary hum deep below the motion of the ocean using seismometers. Undetectable to the human ear, it has been hypothesised that it’s the global pounding of the ocean waves that could be
responsible for this low-frequency vibration.

#4 The Bloop

Lurking deep in the ocean is a sea monster so big it makes the blue whale look tiny, or at least that is what people thought back in 1997 when an almighty ‘bloop’ sound rose from the depths. The sound was picked up by hydrophones across the Pacific and emulated that of a blue whale. However, in order for it to have come from a marine mammal, the owner of the sound would have had to be about the size of the Eiffel Tower! It was later revealed that rather than a sea monster, the bloop was simply the very audible cracking of an ice shelf in Antarctica. Because the original recording was sped up to 16 times its usual speed, the cracking sounded like a big bubble popping, but when reduced to normal speed it sounded like one of the many examples of an ice shelf fracturing.

#5 An Acoustic Aurora

The aurora borealis creates cracking sounds under the right weather conditions

Beneath the flowing light of the vibrant aurora borealis, popping, crackles and an almost static sound can be heard. The explanation for this subtle buzz is not one of spiritual communication, as previously believed, but an electrical discharge from the aurora. These bands of light are the result of solar flares interacting with the magnetic field of the Earth. Combined with a layer of trapped cold air and a build up of electrical charge, this results in the aurora’s static song.

#6 The Bio-duck

Imagine being hundreds of feet below the ocean and through the sonar you hear the sound of what appears to be a duck. As odd of an idea as that is, that was the puzzling reality for a submarine crew in the 1960s. It wasn’t until 2014 that the sound’s origins were identified, and surprise, surprise, it wasn’t a new species of marine duck but the singing of Antarctic minke whales. After 50 or so years of wondering what was quacking, a team of researchers tagged two whales to study their behaviour and movements, but they inadvertently uncovered the truth behind the mysterious sound.

DID YOU KNOW? The loudest sound ever recorded was the volcanic explosion of Krakatoa in 1883, heard 4,800km away!

Written by Scott Dutfield. This article originally appeared in print in How It Works issue 111.

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