How the Mariana Trench Became Earth's Deepest Point
Heavy lava, tectonic movements shaped the 7-mile-deep abyss.
Best known as a Hollywood director and now a National Geographic Society explorer-in-residence, Cameron is one of just three people to dive to Earth's deepest point, and the only one to be able to stay long enough to look around. (Video: Cameron Dive Is an Exploration First.)
Though Cameron and his team are hoping to discover more about the biology of the Mariana depths, geologists already know a lot about how the Mariana Trench formed—and why it's Earth's deepest spot.
(Related: "James Cameron on Earth's Deepest Spot: Desolate, Lunar-Like.")
The Mariana Trench isn't really the deep, narrow furrow that the word "trench" implies. Rather, the abyss marks the location of a subduction zone.
Subduction zones occur where one part of the seabed—in