How deep is the ocean? - The average depth of the ocean is about 3,688 meters (12,100 feet). The deepest part of the ocean is called the Challenger Deep and is located beneath the western Pacific Ocean in the southern end of the Mariana Trench, which runs several hundred kilometers southwest of the U.S. territorial island of Guam. Challenger Deep is approximately 10,935 meters (35,876 feet) deep. It is named after the HMS Challenger, whose crew first sounded the depths of the trench in 1875. This film tells the story of the moving sea floor, from its formation at the mid-ocean ridges, to its demise in the deep-sea trenches thousands of miles away. We compress a journey that takes 200 million years into an incident packed 50 minutes.

We start with the mystery of Hawaii, an island that is sinking, and moving. But why? The first clue came in the Second World War, when a US landing craft commander deduced that the sea floor was moving. To discover why, we dive to the strange underwater world of the ocean ridges where volcanic rock spewing out of the earth creates new sea floor. This is the realm of black smokers, and white chimneys, hydrothermal vents that create their own ecosystem.

From here we descend to the flat landscape of the abyssal plain, where the only features are decaying whale carcasses. Even here, the evidence shows that the seabed is moving. Finally, we see strange mud volcanoes thrown up as the sea floor descends into the deepest part of the ocean, and melts back into the mantle of the earth.

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