Without land, an industrial society will be very difficult to maintain. All natural resources will have to be retrieved underwater. I know we can drill for oil underwater, but what about digging for coal, which provides half our energy? What about mining for uranium? Or any other natural resource?
All of our floating platforms will probably depend mostly on resources that are difficult to get. It will be harder to get metals to make boats. But what about trees? There won’t be any. Nor any of the products we get from trees? Neither will there be any food crops. No corn, no wheat, no soy beans, no apples, no rubber, except as we can create floating platforms for. There won’t be nearly enough of those platforms to support billions of people. And where will the earth come from?
Even if we do have floating platforms, every storm will destroy some of them, and they won’t be replaceable. Maybe engineers will figure out how to use underwater biomass to create new platforms or other things we need, but that will require the development of a radical new set of technologies almost instantly.
Think about weather. With no land anywhere to stop the wind, the storms would probably go on endlessly, like the great red spot on Jupiter. The winds would howl constantly, I bet. It would be very difficult to work in those conditions. It would be hard to keep communities together.
No. I think human kind would die out pretty quickly under such a scenario. The only way “humans” could survive is if we evolved on such a planet, but then we wouldn’t be intelligent. It is doubtful we would have had opposable thumbs. So we couldn’t have wielded tools. In addition, we never would have developed industry because there would be no air to burn things. No foundries. No iron. No industry. No technology. We would be on the same level as dolphins.
Sorry. As a premise for an alternative universe it sucks, unless you assume a different physics where things can burn in water. Now that could be interesting. Think about it.