Question: how deep is the deepest part of the ocean?

Jon Copley answered on 22 Jun 2010:

The deepest part of the ocean is the “Challenger Deep”, which is the deepest spot in the Marianas Trench in the Pacific. It’s almost 11000 metres deep (which is about 6.8 miles). If you put Everest at the bottom of the Challenger Deep, there would still be a mile of water above its summit.

On 23rd January 1960, Don Walsh and Jacques Piccard reached the seafloor at the Challenger Deep in the submersible Trieste. They spent about 20 minutes there, before starting the long ascent back to the surface. They are the only people ever to have actually been there. A Japanese remotely-controlled underwater vehicle (not carrying people) went back in 1995, and an American unmanned vehicle called Nereus also reached the Challenger Deep last year.

Right now there are no submarines that can carry people to the Challenger Deep (the Trieste is not used any more, and is in the Smithsonian Museum in Washington DC). But in January this year, an organisation called the X-Prize Foundation announced that they were offering a prize of $10 million to anyone who could build a new submarine that could take people back to the Challenger Deep on at least two repeat dives within a couple of weeks of each other.

I think a few people will try for this prize over the next few years – possibly businessman and adventurer Richard Branson, and maybe Hollywood director and underwater explorer James Cameron.