[SOUND] [MUSIC] I'm Bruce Fouke from the University of Illinois Urbana-Champaign. We need to put together a framework to understand how all living organisms are related to each other, but also how they have systematically and sequentially replaced each other or moved forward through geological time. And so, we need to think about the idea that nature keeps running experiments of the origination, and the evolution and proliferation of organisms within a given ecological environment. And then, having that environment change. And response of the organisms is to have either all or most of those organisms go extinct. Once organisms go extinct, they're replaced by other organisms that can do better in that environment than they did, because they didn't have the characteristics they needed, the characteristics of reproduction, seeking food, being able to protect themselves. All the things that make it so possible to succeed and be alive in an Earth environment. Organisms have those characteristics. The Earth environment is structured such that they can do well until the Earth environment changes. And then, once that environmental change takes place, then those organisms are the ones who don't do well. They go extinct, and they get replaced by something else. So, in that context, the basic tree of life that was established by Professor Carl Woose at the University of Illinois, that basic tree of life is a three fold structure. There are three basic branches. The branch of the bacteria and the branch of the archaea, the first two branches, those are single cell organisms that reproduce asexually. Then, the third branch of life are the Eukarya. The multi-cell organisms that reproduce sexually, for the most part. So, we want to think about that being the roadmap of life. Then, within those three branches, we want to think about how has life changed systematically through the history of Earth, from very early Earth, when Earth was extremely different from what it is now, chemically, physically, and biologically, too. And Earth that we know of in the modern-day environment. So, we want to put the template of a changing Earth on top of the three branches of life. And the way we do that, then, is as we move up the three branches of life then we can evaluate the upper parts of the tree and how they branch. Each of those branches in the upper parts of the tree of life are representing changes through evolutionary biological processes that create and form different kinds of life as time goes forward. So, what we want to do is look at an Earth where we were moving from having single cell organisms only, to multi-cell organisms. And the advent of the incredible radiation and diversification of these Metazoans, the multi-celled organisms, and having the Metazoans go from having an organism that has no skeleton to an organism with skeleton. Because once the skeletons were formed by Metazoans, and that's what we define as the Cambrian Explosion at 543 million years before present, everything changed in terms of the development and the structure of how Metazoans could interact with their environment. So, the way we do that is that we consider, first of all, what were the primary natural experiments that nature had run in order to see how these things fit together in the puzzle pieces. And so, one of the first ones that were run by nature was called the Ediacaran Fauna. And this was a group of organisms that were Metazoans, they had no skeletons. And they came on board, they originated, they radiated right after a catastrophic event in Earth history called the Snowball Earth. This group of unique organisms, though, they themselves went extinct. They were relatively short-lived, and they were replaced by a group of organisms that were Metazoans that had skeletons. And the skeletons at first were all exoskeletons. They were on the outside of the body of the organism. And then, as time evolved through the Phanerozoic, then we saw the advent of Metazoans being able to synthesize and secrete a skeleton that was interior. And we call those vertebrates. So, we move from an invertebrate Earth to an Earth that had both vertebrates and invertebrates. And we see how that structural design feature allowed them to really do well in these evolving Earth environments, both in the terrestrial environment and in the oceans. Within that grouping of geological time that goes from the 543 million year Cambrian explosion through the modern, we call that the Phanerozoic. And that Phanerozoic is broken into three primary groups of what we call Fauna. And the Fauna are the groupings of animals. The first grouping of animals was called the Cambrian Fauna. The second grouping of animals was called the Paleozoic Fauna. And the third grouping of animals was called the Modern Fauna. And then, the changes sequentially going from the Cambrian Fauna into the Paleozoic Fauna into the Modern Fauna, it was benchmarked. It was truncated. t was defined by Earth processes. One of the most important of which was meteor impacts. So, when large meteors slammed into the Earth, they caused a lot of organisms to go extinct. And each time those massive extinction events took place, then nature would respond by, once the catastrophe took place and some geological time went forward, then new organisms evolved and moved into those ecological zones that were previously inhabited by another type of organism. And we see that there's this basic threefold structure of having organisms respond to new and open ecospace in which they could radiate and evolve, and then have the whole system reset by meteor impacts. So, the Cambrian Fauna, the Paleozoic Fauna and the Modern Fauna. And that's the template of the evolution of multicellular organisms with skeletons, both internal and external. That defines and sculpts the shape of one of the primary three branches of life, which are the Eukarya. Moving forward from here, we want to then start to look at the idea that that Eukarya branch in history was also interfacing all the time, not only with a changing planet, but also with microbes, bacteria and archaea. And one of the great challenges of science is to be able to understand how all these multiple branches of life are developing, and how they interact with each other to influence each others ability to survive in an ongoing changing planet. [MUSIC]
