About 575 million years ago, multicellular life forms started taking over the world's oceans. There was an explosion of new and diverse types of living things that we call the Avalon explosion. This timeline coincides with a rise in the oxygen levels of the deepest parts of the oceans. For a long time, scientists have assumed that the rise in oxygen led to better conditions for reproduction and for new and different species to arise. It makes sense, but it might not be true at all. More recent findings hint that the explosion of species may have happened before the great infusion of oxygen. What does that mean? It means we have a lot more to learn, and that we shouldn't assume we have things figured out.