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James Cameron dive launches race to the bottom of the world (+video)

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Although deep-sea trenches make up only about 1 percent of the sea floor, they are of keen scientific interest. They form as old, dense oceanic crust, long ago made by lava welling up along mid-ocean volcanic ridges, now is pushed beneath more-buoyant continental crust.

The process creates a long, canyon-like boundary. The Mariana Trench, for instance, has an average width of about 43 miles but narrows to a slot-like valley at the bottom, nearly 7 miles below the ocean surface.

With crushing water pressure – roughly 1,000 times air pressure at sea level – and temperatures hovering around freezing, the environment at the bottom of these trenches is home to an unusual assortment of creatures. Last summer, for instance, a team from the Scripps Institution of Oceanography in La Jolla, Calif., and the National Geographic Society found that a super amoeba – a single-cell organism measuring about 4 inches across – was inhabiting depths two miles deeper than previously believed.

The creatures, known as xenophyphores, also host a range of other, multicelled organisms.

Samples of trench communities have turned up a range of more complex creatures, including shrimp, fish, and soft-shelled snails uniquely adapted to their harsh home.

The sea floor Cameron saw, however, was barren, he told reporters. He said never reached a place that looked to host any interesting biology.

For the creatures that do live in the deep, researchers are trying to figure out where they get their food, as well as the pecking order in the food chain at such depths.

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