Detailed Instructions: In this task, you are given a text of many news articles seperated by special token "|||||". Your task is to summarize them.
Problem:Our blue planet spins suspended in outer spaceâ€”and it hums, too. 
  
 European researchers say the Earth's incessant hum originates from the bottom of the ocean. This study, published by researchers from the Paris Institute of Global Physics in the journal Geophysical Research Letters in November, gleans material from ocean-bottom seismometer stations, contrasting with previous data from vibration tools based on land. 
  
 "It's like taking a piano and slamming all the keys at the same time," says Spahr Webb of Columbia University's Earth Institute, who was not associated with the study. "Except they're not nice harmonics. They're oddball frequencies." 
  
 Humming by the Numbers 
  
 The planet's hum has tickled scientists' minds since 1959, but definitive research was not completed on the topic until 1998. This current paper is the first to document the rumble from the bottom of the ocean. 
  
 The researchers, spread out across earth science institutes in Paris, Stuttgart, and Oxford, U.K., combed through 11-months' worth of seismometer records covering a patch of more than 1,200 square miles on the Indian Ocean floor east of Madagascar. From that data, gathered from 2012 and 2013, they homed in on two stations with high quality data and sliced out any interfering sounds from loud waves and electronic glitches. Behold: the native sound of the Earth. 
  
 But the terrestrial hum is virtually silent. 
  
 The planet's vibration, or record of "free oscillations," hovers between 2.9 and 4.5 millihertz. That's a frequency 10,000 times lower than what humans can pick up; our hearing threshold starts around 20 hertz. 
  
 The researchers also found that the hum's amplitude, or loudness, did not vary over time. However, the sound change didn't depend on the seasons, which goes against other studies surveying a wider band of frequency, or pitch, than the one looked at in this study. 
  
 Related: Here's What Earthquakes Look Like From Inside The Earth 
  
 "To better understand where the signal comes from, we believe that observing oscillations from the ocean bottom can help," says co-author Martha Deen. 
  
 Looking Forward 
  
 The Earth's hum is nothing new, Webb says. When looking at early seismometers, scientists saw the instrument's needles swing back and forth for a few seconds at a time, which they attributed to regular rumbles. They looked at ocean waves that produced pulses of pressure when traveling in opposite directions, and deduced that longer waves interacting with the bottom of the ocean are probably what's driving the Earth's hum. 
  
 "Fairly early on, people realized this was caused by ocean waves," Webb says. "As instruments have gotten better, we've realized the hum's going on all the time." 
  
 Since early observations, a number of studies have hypothesized that the Earth's free oscillations are a side-effect of the pounding of ocean waves. Other research suggests the hum could originate from atmospheric turbulence, or the wind motions around the globe, cued by storms. The current study says turbulence could account for part of the vibration, leading the rest to be fueled by ocean waves. 
  
 But not everyone agrees. "Turbulence in the atmosphere is moving very, very slowly. It's not energetic enough," says Webb of Columbia. "The hum is solely associated with ocean waves." 
  
 By studying the Earth's hum signal from ocean-bottom stations, scientists can map out a detailed landscape of the Earth's interior. Currently, they can only look at the inside of the planet during earthquakes, which limits studies to certain times and areas. And when looking at seismic activity from land monitors, researchers can't chart places far removed from islands and land masses. But the hum signal, droning and constant, can be detected across the world. 
  
 "That can be used to map the structure of the Earth," Webb says. "Getting data from new places is going to help." ||||| Far from the blaring cacophony of cities, towns and suburbs, there are far quieter soundtracks to be found — the murmurs of wind rustling grasses, rushing waves tumbling onto beaches, the creaking of tree branches and trunks. 
  
 But underneath all that is yet another soundscape, a permanent, low-frequency drone produced by Earth itself, from the vibrations of ongoing, subtle seismic movements that are not earthquakes and are too small to be detected without special equipment. 
  
 Earth is "humming." You can't hear it, but it's ongoing. And now scientists have measured that persistent hum from the ocean floor, for the first time. [What's That Noise? 11 Strange and Mysterious Sounds on Earth & Beyond 
  
 Most of the movements in the ground under our feet aren't dramatic enough for people to feel them. Earthquakes, of course, are the big exception, but Earth undergoes far more earthquakes globally than you might suspect — an estimated 500,000 per year, according to the U.S. Geological Survey (USGS). Of those, 100,000 are strong enough to be felt, and about 100 of those are powerful enough to cause damage. 
  
 But even in the quiet periods between earthquakes, there's a whole lot of shaking going on. 
  
 Since the 1990s, researchers have known that Earth is constantly vibrating with microseismic activity, known as "free oscillation," scientists reported in a new study describing new recordings of the phenomenon. Free oscillation creates a hum that can be detected anywhere on land by seismometers — equipment used to detect and record vibrations. 
  
 For years, the source of this perpetual humming stymied researchers, with some suggesting that the rhythmic ebb and flow of ocean waves that reached all the way down to the seafloor were responsible, while others attributed the vibration to collisions between ocean waves. Then, in 2015, scientists determined that both types of ocean movement played a part in keeping Earth vibrating, Live Science previously reported. 
  
 While seismologists have recorded and measured Earth's hum on land, they had yet to capture evidence of the planet's sonic stylings from the ocean depths — until now. 
  
 Recently, scientists traveled to the seafloor in the Indian Ocean to capture the humming sound, using special spherical ocean seismometers. Between September 2012 and November 2013, the researchers deployed 57 free-fall seismometers around La Réunion Island to the east of Madagascar, over an area measuring about 772 square miles (2,000 square kilometers), they wrote in the study. 
  
 Using filters, noise reduction and calculations, they isolated the hum from normal ocean noise levels generated by ocean wave motion and seafloor currents, and found "very clear peaks" that appeared consistently over the 11-month study period, and which appeared in the same amplitude range as measurements of the humming taken on land in Algeria, the scientists reported. They noted that the peaks occurred at several frequencies between 2.9 and 4.5 millihertz — about 10,000 times lower than the human hearing threshold, which is 20 hertz. 
  
 Capturing ocean recordings of Earth's hum will provide scientists with far more data than is currently available from readings taken on land, contributing to efforts to map the planet's interior, the researchers wrote in the study. 
  
 The findings were published online Nov. 27 in the journal Geophysical Research Letters. 
  
 Original article on Live Science. |||||
Solution:
The Earth hums, and scientists have for the first time recorded the sound in the ocean. Using seismometers in the Indian Ocean, researchers picked up on the sound that is way, way too low for mere human ears to hear, reports Live Science. No recording is available, but a Columbia University scientist not involved with the study in Geophysical Research Letters gives National Geographic a rough description: "It's like taking a piano and slamming all the keys at the same time," says Spahr Webb. "Except they're not nice harmonics. They're oddball frequencies." And ultra-low ones: Specifically, the hum is between 2.9 and 4.5 millihertz, and humans can only begin hearing things at about 20 hertz, or roughly 10,000 times higher. While scientists have long known about the hum, and have previously recorded it on land, the new research could shed more light on the Earth's interior, and perhaps even help map distant planets, reports the Washington Post. The leading theory is that the hum is caused by waves interacting with each other at the bottom of the ocean, which results in vibrations being sent down into the Earth's crust. The process, however, is complex and not fully understood. For instance, "sometimes a wave on a shallow coast somewhere ripples over the rough sea floor and adds its own frequencies to the hum," per the Post. Whatever the exact reason, one thing is clear: the low drone is a constant one. Read more speculation about the hum here.