The Evolution of Bacteria

There is actually a period of earth's history that's sometimes called the boring billion by bioles, because it was literally billion years of time where very little seemed to have happened. But generally, it seems lake we should count the really tricky transitions. For example, making an eye has been done by a lot of different species of animals independently. So it seems like evolving ice is not terribly hard, given a few hundred million years of trial and error. On the other hand, as far as we know, there has only been one transition from procario to a carrions. And tried to say something about how often do they happen?