Under water I always imagine that a biological revolution would be more likely, and technologies that evolve (so to speak) out of organisms that make deposits l

Under water I always imagine that a biological revolution would be more likely, and technologies that evolve (so to speak) out of organisms that make deposits like coral. So you would have a "limestone age", followed by something harder. At some point metals would come into the picture, but it would likely look very different than our "tech tree"/