Imagine a world with no land at all, merely the impenetrable depths of a seething ocean. Models of planet formation predict the existence of such worlds, even though our own solar system has none. Indeed, their formation should actually be rather common — and new satellites may soon detect them around other stars.
So, Drake question now has another type of world to consider. Not only could hot jupiters disrupt their way across the habitable region, a large portion of the water baring worlds are ice apped like Europa, and a large portion of the planets that form, period, are gas giants, if this guy is right, then there is yet another kind of world that's not so friendly to spacefaring civilizations out there that negatively impacts the equation: waterworlds. They may even be common.