@Stevo: Space is rather less dense that the ocean and far and away more easily, though not cheaply, explorable.
That said, it would be nice for us as a species to ocean better.
Also, the ocean is less dense than at least one billionaire.
@Stevo: It's a depth of roughly half the height of Mt. Everest's highest peak, and per square inch the pressure is 6,500 lbs., nearly 400x that of air pressure at the beach. Light barely reaches to any meaningful depth in the oceans, and sound is the only thing that transmits, however dicily at long range. It's hard to find what you can't see or hear at all unless you're on top of it. The North Atlantic is around 16 million square miles, breadth and depth. That's why we rely on cables, alas.
@Stevo: The pressure/sq.in. at the Titanic's depth is roughly that of the Space Shuttle engines at liftoff.
As a Cold War submariner wrote years back, when you're down at max depth, it like you're in a tin can in an Olympic swimming pool full of concrete.