The valley in question is the Challenger Deep, and is the deepest recorded point on the earth's seabed, according to the South China Morning Post. At such depths, sound is crucial for communication, since there is no light.

The researchers were able to hear sounds from the deepest part of the ocean and they've left six acoustic sensors in the trench to collect information about ambient sea noise for a year. These will be retrieved in November. This is the first such experiment for China, and its results could not only help understand how deep sea creatures communicate with sound, but could also have military applications.