User blog comment:David Rain/ATL idea. Odd, but Cool./@comment-4940710-20120613041630

Well as others have pointed out, aquatic life (at least as we know it) would be unable to survive during winter, since it would be pushed up to the surface as a result of layer after layer of water freezing.

I wouldn't write your off as totally implausible, but there would be two PODs that would be absolutely necessary. The first would have to be 15 billion years ago, with the universe developing in such a way that water has the same fundamental properties as all other substances with regard to the relationship between temperature and density. The second would have to be 4.6 billion years ago, with the first microbes to come into existence having the ability to survive outside water.