If a ship passes over the deepest part of the ocean but there’s nobody there to hear it, does it still make a sound? It sure does. New audio recordings from the Mariana Trench, the deepest part of the world's oceans, have captured the sounds of whales, distant earthquakes, storms, and even ships passing tens of thousands of feet above.

Challenger Deep is a valley inside the trench, seven miles below the surface of the ocean. To give you some idea of just how deep that is: If you chiseled Mount Everest off its foundation and dropped it into the Challenger Deep, the mountain’s peak would still be a mile underwater.

Image credit: Center for Coastal and Ocean Mapping - Joint Hydrographic Center

The valley is of great scientific interest, but its distance from the surface and the tremendous amounts of pressure down there have made it hard to study. A team of engineers created a special titanium-coated hydrophone, or underwater microphone, but even they weren’t sure it would work.

"We had never put a hydrophone deeper than a mile or so below the surface, so putting an instrument down some seven miles into the ocean was daunting," engineer Haru Matsumoto said in a press release. "We had to drop the hydrophone mooring down through the water column at no more than about five meters per second. Structures don't like rapid change, and we were afraid we would crack the ceramic housing outside the hydrophone." 

Researchers dropped the hydrophone over the side of a ship. More than six hours passed before the equipment reached the valley floor, but once it did, it began recording. When the research team collected the hydrophone, they brought up 23 days' worth of noise from the bottom.

"You would think that the deepest part of the ocean would be one of the quietest places on Earth," chief project scientist Robert Dziak said in the press release. "Yet there really is almost constant noise from both natural and man-made sources. The ambient sound field at Challenger Deep is dominated by the sound of earthquakes, both near and far was well as the distinct moans of baleen whales and the overwhelming clamor of a category 4 typhoon that just happened to pass overhead. There was also a lot of noise from ship traffic, identifiable by the clear sound pattern the ship propellers make when they pass by."

Curious what those “distinct moans” and that “overwhelming clamor” sound like? Listen for yourself:

The Challenger Deep soundtrack is impressive on its own, as both scientific data and a demonstration of human ingenuity. But it’s also an indicator that our effects on the environment reach farther than we could have imagined. Scientists now know that anthropogenic (human-created) sound wreaks havoc on marine ecosystems, from the largest whales to the smallest fish eggs on coral reefs. From city streets to the Challenger Deep, our noise is more than just noise.