[MUSIC] Nature has run a series of experiments through time. We call it evolutionary biology, we call it the interaction of life with Earth, but in the end, it's been a series of ongoing experiments. And the experiments are that there are these natural conditions in which life can emerge into, evolve into, originate, change, adapt, do well in those environments but then there's environmental change. You can change the temperature. You can change the food source. You can change what eats who. You can actually make a predator when there were no predators. You change the dynamics of the landscape in which these organisms are living, and those dynamics change systematically with time, as the Earth itself changes, and as the interactions with Earth and life change. So, all the puzzle pieces are moving, and shifting, and interacting differently with time and changing. So, within that template then nature has run a whole series of experiments, and those experiments are what survives in what kind of conditions, and if you don't have the right attributes, the right kind of physical size, the right kind of ability to eat, the right ability to reproduce. If you don't have whatever that right mix is, and you're not fit, fitness is the ability to to actually succeed in reproducing and putting your genetic code into the next generation. If you're not fit, and you're not succeeding and you're not thriving then you're going to go extinct. And nature has done this over and over again. But the thing to think about is the very first time this happened with metazoan organisms. The multicellular organisms that primarily evolved starting at the Cambrian Explosion, which was 543 million years ago. But Just before that time period, the Cambrian is defined by multicellular metazoans that exploded and evolved that also made skeletons. Nature ran experiment just before that time period, near the end of the Proterozoic when metazoans proliferated, they just exploded within the especially the marine environment. And those organisms had no skeleton. So there was a very unique experiment that nature ran and it's called the Ediacaran Fauna. And the Ediacaran Fauna is named after a location in Australia where some of these amazing fossils were found. So these are towards the end of the Proterozoic. Something on the order of approximately 0.6 billion years before present. Now, another thing about the Earth at this time period as we look at these unique organisms of the Ediacaran Fauna is that the idea the Earth had just come out of one of its great catastrophes, and that was the entire Earth froze. We had the development of ice sheets from both poles that were moving towards the equator and they not only got close to the Equator, but there's pretty good evidence in the fossil record that there was sea ice on the Equator. So we had about two meters of ice that was covering the ocean at the Equatorial Zone. We don't have anything close to that in the modern, right? But But we had a frozen Earth, and so that frozen Earth we call Snowball Earth. A series of geological events brought us out of the Snowball Earth. CO2 was introduced to the atmosphere at high levels due to volcanic eruptions. There are some other processes that happened the redistributed heat, and distributed microbial life differently throughout the Earth. So we had a series of events that took place to bring us out of a frozen planet, called the Snowball Earth. But as we moved out of the Snowball Earth, and before we got to the first multicellular organism with a skeleton, we had a tiny sweet spot of time, and that's the Ediacaran Fauna. That was a group of organisms that arose very different in anything we have now. They had no skeletons. So the Ediacaran Fauna, again named after a location in Australia where there are many of these fossils, were the following. They were like large jellyfish. Kind of masses of gooey, gloppy material that were well structured. They had a shape to them that were very distinct, but if you were to touch them or grab them under water They'd be kind of like jell-o. They had cells but there was no structural support for those cells. And some of the shapes and forms we see are quite bizarre. One of them looked like a quill of a writing pen, where you had a stock that attached to the sea floor and then coming off that stock you had a shape that looked like a large leaf or a quill on a pen. And that was one of the many types of these organisms, and one of their hallmarks was that these Ediacaran Fauna organisms, the metazoans at that time, they had bilateral symmetry. So that meant that if you were to take have the organism and put a mirror up against it. If you looked in the mirror you'd see the other half being reflected. Well the other half that actually grew was in the shape of that reflections so if you run a line right down the middle of the organism both sides of the organism are identical. So there's bilateral symmetry was utilized by the evolutionary biology design that was going on by nature at that time period. Then, in this group of organisms, we had the ones that lived on the sea floor, and stocked. And when something makes a lifestyle on this floor of the ocean, we call that benthic, and so, benthic organism were a major part of the Ediacaran, but we also had another group of Ediacaran Fauna that actually lived in the water column. So, those that swam and moved around with the currents. So we had all these kind of organisms inhabiting these different ecological spaces on the sea floor in that time period. And it was a relatively successful group of organisms. But then those organisms went extinct and we don't know all the factors that came into play with those. But we believe the following, that one the earth was changing its environmental composition if you will. The oceans were evolving and there might have been ecological environmental constraints that were being placed on those organisms that weren't there at the time they evolve. So again, natural selection as the environment changes the organisms without those characteristics of how they eat, how they reproduce, their size, their relationships to things like currents. If those weren't all in the correct configuration as the environment changes, they're going to go extinct. So we think the environmental change was part of that, but also towards the end of the Ediacaran Fauna, that's when we had the Cambrian Explosion. We had the emergence of some of these organisms that started having these skeletons, so we don't know all the answers to this. But in the end, we do know that group of organisms went extinct, and we've never seen anything like it, both in terms of its symmetry, the fact that we have such larger organisms that were totally without any kind of skeletal support whatsoever. Very, very unique, very rare, and it hasn't happened again in terms of evolutionary biology. So the Ediacaran Fauna is a sobering look at evolutionary biology. Some things work, and some things don't. And if you would have come onto the planet at the end of the Proterozoic, all of the organisms you saw that were large and multicellular in the ocean, they would all have been part of the Ediacaran Fauna. Yet they all went extinct at the time then that we transitioned into multicellular organisms with the skeleton defined by the Cambrian Explosion. [MUSIC]
