The sea, Antarctica, the Moon -- all these places can technologically be colonized, but it won't happen until there's some compelling economic reason for it --

The sea, Antarctica, the Moon -- all these places can technologically be colonized, but it won't happen until there's some compelling economic reason for it -- either an industry which can make money there (see colonization of South Africa, South America), or a bunch of colonists willing to pay their own way for long enough until the colony becomes self-sufficient (see colonization of North America). Come to think of it, we already have colonies on the ocean floor, they're called oil rigs, and they're economically viable. I wouldn't want to live there, though.