"It's the last frontier for science and exploration on this planet," said film director James Cameron of the Mariana Trench, seven miles down in the western Pacific. Entrepreneur Richard Branson and former Google CEO Eric Schmidt are planning their own separate trips to explore the trench in deep-water submersibles. (National Geographic via Associated Press)

"It's the last frontier for science and exploration on this planet," said film director James Cameron of the Mariana Trench, seven miles down in the western Pacific. Entrepreneur Richard Branson and former Google CEO Eric Schmidt are planning their own separate trips to explore the trench in deep-water submersibles. (National Geographic via Associated Press)