Nearly all of Earth's largest geological formations are found on the ocean floor,

Everest is the tallest mountain on terra firma. From its base at sea level to its peak near the top of the troposphere, Everest measures in at 29,029'. Hawaii's Mauna Kea is a dormant volcano and the world's highest island-mountain. Mauna Kea stands on the ocean floor, 18,200' below sea level, and peaks 13,796' above the water line, making it about 32,000' tall. Right next-door, Mauna Loa is an active volcano which makes up more than half of Hawaii's surface area. Mauna Loa also starts off at the seabed and in a geologic photo-finish, comes in just a nose shorter than Mauna Kea at 31,880'.The Grand Canyon is king of all continental chasms but it is not nearly so grand when compared to the largest fissure in the seafloor. That dramatic drop-off is 120 times larger than its land based counterpart and it developed where the Pacific tectonic plate pushes under the Mariana plate. Located just east of the Mariana Islands, the underwater abyss called the Mariana Trench is the deepest crevasse in Earth's crust. The tale of the tape for the Trench is 1,580 miles long, 43 miles wide on average and a maximum depth of 36,070' at a spot aptly known as Challenger Deep. So if Mauna Kea was moved into the Mariana Trench, the world renowned telescopes near the top of that mountain would have an obscured view of the stars since they would be more than 4,000' under the surface of the sea.Covered by nearly 7 miles of seawater, the bottom of the Mariana Trench is like no other place on the planet. The overwhelming weight of that much H2O creates a pressure which is 1,000 times greater than what we feel at sea level. Like a gigantic clenched fist, the ocean at that depth exerts the enormous force of 8 tons per square inch. Even the water itself, which is usually considered incompressible, gets compressed at that pressure. Such an uninviting environment explains why so few people have ever been on the bottom of the Mariana Trench.

Listening to the retrieved recordings for the first time, the project's scientists did not hear the nearly silent sea that many were expecting

Compared to the base of the Mariana Trench, the moon is a tourist trap; over crowded and way over priced. A dozen people have landed on the moon then walked on the lunar surface. Six of them even went joy riding in the lunar rover. Using deep-diving submersibles, a total of three people have reached the lowest point of the Mariana Trench and none of them ever considered walking around down there since they knew that water pressure would puree them into paste the instant the hatch was cracked open.In 1960, the USN bathyscaphe Trieste was the first manned submersible to descend to the bottom of Challenger Deep. The two man crew, Don Walsh and Jacques Piccard, spent only 20 minutes on the seafloor and were not able to take any pictures due to the clouds of sediment stirred up by the Trieste's propeller. Over half a century later in 2012, James Cameron became the third and last man to land on sea's lowest spot. Cameron was able to explore down there for hours and shoot enough film to make a movie, the Deepsea Challenge 3D , which documents that voyage to the bottom of the Mariana Trench.Along with the two manned missions, a number of remotely controlled deep-diving submersibles have also explored Challenger Deep. On those dives many measurements were made and samples taken to study the physical properties and biology of the abyss. The observations revealed a world of complete darkness where temperatures are always within a few degrees of freezing and vise-like pressure compresses the water by nearly 5%. Naturally, the place is teeming with life , since that's just what life does: adapt and thrive when given even the slightest chance to do so.While the submersibles sent to Challenger Deep had lights and cameras to film what the bottom of Mariana Trench looked like, they did not carry any equipment to record audio from the abyss. So no one knew what the sea sounded like at that great depth. Would the narrow shape and remoteness of the trench insulate the deepest part of the ocean from any sound waves, or would the enhanced acoustics of its compressed water act to amplify those waves? The existence of sound at the bottom of the sea remained a mystery until just recently.In July 2015, a team of researchers from NOAA, Oregon State University and the U.S. Coast Guard spent three weeks eavesdropping on Challenger Deep. From the deck of the Guam-based Coast Guard cutter Sequoia, the crew lowered an array of titanium-encapsulated hydrophones down 36,000' until the recorders reached the ocean's deepest depths. Once safely in place on the seafloor, the instrument package was remotely switched on and left to record. The hydrophone's flash drive was filled with recordings in about 23 days but the equipment could not be recovered until last November due to the heavy typhoon traffic set up around the Trench by a strong El Niño . When the cutter was able to get back on site, the researchers sent down an acoustic signal which released the instruments from the ballast that had secured them to the seabed and the hydrophones slowly ascend from the depths back to the surface.Listening to the retrieved recordings for the first time, the project's scientists did not hear the nearly silent sea that many were expecting, but a surprisingly noisy place instead with almost constant clamor. For the last several months the researchers have been separating the cacophony into individual sounds. They have been able to identify both natural and man made sources, including the call of baleen whales, waves disturbing the surface, passage of a Category 4 Typhoon, the rumble of a magnitude 5 earthquake that occurred above the level of Challenger Deep and the distinctive whirl of ship's propellers.Earlier this month, an analyzed and edited version of the Challenger Deep recordings was released to the public. Now for the first time ever we can listen to a sample of some of those sounds from the bottom of the sea.





