Seven miles to the bottom of Pacific's Mariana trench
Avatar director James Cameron's attempt to be the first human being in 50 years to visit the deepest point on Earth - the bottom of the Mariana Trench, seven miles down in the Pacific - is under way.
The director aims to become the first of at least four teams racing to the ocean floor, an icy, alien environment with pressures 1,000 times higher than the surface.
Many liken the journey to man's steps into space. ' The deep trenches are the last unexplored frontier on our planet,' says Cameron.
The only people who have ever reached the bottom of the Mariana Trench were Jacques Piccard and Don Walsh, who used the huge, blimp- shaped submersible Trieste in January 1960.
The director recently completed a test dive of five miles in Papua New Guinea, using his solo submersible Deep Sea Challenger.
Cameron had to build his own vehicle for the attempt - a craft capable of withstanding 1,000 atmospheres of pressure.
Cameron is inside a pilot sphere - the shape most able to resist pressure - so cramped he will not be able to extend his arms.
He will be the sole occupant in a complex, 24-footlong craft made primarily of highly specialised glass foam.
The descent will take around 90 minutes and he will spend around six hours at the bottom, filming the attempt for a 3D documentary.
A unique Rolex watch will also be journeying to the bottom with Cameron.
Rolex sent a watch down with the Trieste in 1960 and produced another timepiece for Cameron's odyssey.
It's a complete one- off and not for sale - and is capable of withstanding the extreme pressures of the Mariana Trench - and more - right down to 12,000m.
Cameron looks set to beat rival teams to the bottom - Sir Richard Branson's Deep Flight Challenger, and DOER Marine, backed by Google's Eric Schmidt.
A Florida company, Triton submarines, are working on a submarine that will take people to the bottom for $250,000 a ticket.
'I've always dreamed of diving to the deepest place in the oceans,' says Cameron. 'For me it went from a boyhood fantasy to a real quest, like climbing Everest.'
' There is currently no commercial submersible on Earth capable of diving to the 'full ocean depth' of 36,000 feet. The only way to make my dream a reality was to build a new vehicle unlike any in current existence,' says Cameron.
A ' hydrographic' ship from the U. S. Navy recently mapped the Marianas trench from north to south using a ' multibeam echosounder', a standard device for mapping the ocean floor.
The ship, associated with CCOM, the Centre for Coastal and Ocean Mapping at the University of New Hampshire, mapped the whole of the Marianas Trench to a 100m resolution - including an accurate 'map' of the deepest place on earth, Challenger Deep
Cameron is an avid explorer with 72 submersible dives to his credit-51 of which were in Russian Mir submersibles to depths of up to 16,000 feet, including 33 to Titanic.