Scientists from NOAA have recently released audio recordings taken from the Mariana Trench, the very deepest part of the ocean. Strangely enough, sounds from humans, animals, and the earth itself can be heard echoing in its dark depths. link
Researchers sunk a hydrophone 36,000 feet into the Challenge Deep in the Mariana Trench in an effort to establish some baseline for oceanic noise. They were, logically, expecting to capture nothing more than silence - given the remoteness of the trench and its depths.
Much to their surprise, over the course of several weeks, they were able to capture whale calls, ship propellers, earthquakes, and the sound of a category four typhoon passing above.
How is this possible?
Well, sound waves travel around 5x faster through water than through air. In addition to the speed, they also have to deal with fewer disturbances and obstacles, which helps them travel further distances.
One of the main reasons NOAA conducted this 23 day study was due to the prevalence of noise pollution. Human generated noise pollution, like ship propellers, have been often linked to disruptions in marine life behavior. At close to the bottom of the Mariana Trench, researchers thought they would be too far away from these disturbances to hear a thing.
There is a return investigation planned for 2017 to see if noise levels have increased.