In an earlier post I said that evolution was not progressive. By this I mean that there is no intent or objective of evolution and it is not trying to achieve a goal. There is however an appearance of progress and this is because of natural selection discovering novel solutions to problems.
Once one of these novel solutions becomes available then this can open up a completely new direction for evolution that was previously inaccessible. It is these breakthroughs that create the picture of punctuated equilibria. One of these changes was the production of oxygen and the changes that this brought about in the atmosphere driving the anaerobes from the Earth's surface. Another example is the creation of multi-cellular life.
Once these possibilities have been accessed then short of massive world wide extinctions that eliminate all of the organisms that have exploited these new variations then they will remain part of the evolutionary repertoire. So evolution has a ratchet that does not allow apparent progress to be forgotten, much the same as we cannot forget that we have created nuclear weapons and other inventions we wish we had not discovered.
But this does not mean that some of these steps are not actually more than historical accidents that may actually lead to the long-term extinction of species that utilise them. Oxygen consumption might not be the best solution for the long run, but we are stuck with it while the atmospheric composition remains at its current levels. Trees are a good solution at current levels of carbon dioxide, but they are less successful at lower levels where grasses become preferred.