[SOUND] [MUSIC] The structure of the universe lays a road map and a template for us to think about how life has evolved. Life itself is made out of the same stardust that everything else is made out of, and so it's part of a continuum. And therefore, one without the other, you can't really understand the context of the structure of life and the history of life. So let's just visit, briefly, what we know about our solar system and how the structure has come to be. The first thing is that we know there's a good recent TV show called the Third Rock from the Sun. And so we do live on the third rock, but as you look at the structure in the universe we now have eight planets instead of nine. Poor Pluto was the last planet. It was kicked off the list because it wasn't big, and bad, and tough, and in the right orbit enough to remain as a planet. So we have eight planets, and the way that we view that universal solar system structure is, it's pretty simple. It's broken into a couple parts, one are we have a series of four planets that are the closest to the sun. And we call those the terrestrial or rocky planets, and those planets include Mercury, Venus, Earth, and a very well known planet, Mars. So, the inner terrestrial rocky planets, and they call them that because they are hard, they're solid, they're rocky, and they're relatively small compared to the other planets. And the other group of planets they go outward from there, the other four planets, we call them the giant gas planets or the Jovian planets. And these are significantly larger, many times larger than the inner rocky planets. And they have an inner rock metal core in the center, but the vast majority of the planet are all of these circulating seas, if you will, of gases that are swirling and rotating around this very relatively small core. The ones that make up that group are Jupiter, Saturn, Uranus, and Neptune. Again, Pluto's been knocked off the list, but I will say that there are some suggestions that, that should be reconsidered but we won't go to that discussion at this point. In addition to these eight planets, we have a grouping of rock, dust, and ice, and garbage debris if you will. All kinds of particles and chunks, and rock fragments that never made it into a planet, but are still moving around throughout the solar system. So, the three I want to talk about that are important because they also speak to this idea that they are the source areas for the meteors that end up hitting the Earth and causing mass extinctions and great destruction. The first one is called the asteroid belt. So the terminology here is that when a body is moving through space, we call that a meteor, and meteors can be composed of two types. One is composed of solid rock and we call that an asteroid. One is composed of primarily ice and then rock fragments and that's called a comet. So the asteroid belt is again primarily formed of these very large pieces of rock that are whirling through the universe. And the asteroid belt is just to the outside of Mars. And this speaks to the idea that through history Mars has been a lot less lucky than Earth has been, and lucky in respect to how many times meteors have pulverized and hit the planet. We've had plenty on Earth, but we've had a lot more on Mars. And one of the reason Mars is currently a cold, desolate place with we hope the potential for life in the subsurface, is because simply put, they were bombarded with meteors that came in from the asteroid belt. Another really important grouping of bodies in the universe, in the solar system, we call it the Kuiper belt. And Kuiper was the name of the scientist who identified these originally. And this is a group of comets, again the water and rock debris chunks that are flying through the universe. And those occur just beyond Neptune. So we have the asteroid belt serving up Earth and Mars and other planets with plenty of asteroids, the Kuiper belt serving up comets. And then the last one is another group of comets that we call the Oort Cloud. And the Oort Cloud is at the very most outer reaches of our solar system. And so these three belts, the asteroid belt, the Kuiper belt and the Oort Cloud, are sourcing primarily the groupings of asteroids and comets that then end up slamming in to planet Earth. Now, another thing to think about is that the advent of the Hubble Telescope, the incredible telescope that is now in space, in orbit around the planet. By focusing the Hubble Telescope at some of the farthest reaches of the solar system that we can see from Earth orbit, we have a brand new appreciation of what the structure of the universe is. But one of those is just simply how amazing the number of stars are. And then in concert to that is how many planets could be around those stars. So right now our current sun in our solar system is one of only 300 billion stars, so 300 billion, and that's in the Milky Way alone. And then with the findings of the Hubble Telescope, we now know that there are many orders of magnitude, many, many more solar systems that have not even been mapped throughout the universe. So the Milky Way is one of hundreds of hundreds of billions of galaxies and solar systems that are just visible. And then there is a whole other suite of these that we can't see yet, so the idea is that our solar system, as amazing, and complex, and dynamic as it is, is just one tiny fleck or sliver of the total number that are out there. So this structure of our solar system, the rocky planets, the Jovian gas giants, and then having an asteroid belt, a Kuiper belt, and an Oort Cloud, that's the structure then, that's the dynamic that is allowing us to have, through geological time and it'll happen again in the future, regular bombardment of the Earth by meteors. And when a rock body, an asteroid, or a comet is flying through the universe, we call that a meteor, but then when it slams into a planet, or in our case slams into the Earth, we then call that a meteorite. So the meteorites that we find on Earth have given us a lot of information about the solar system, and that's another piece of evidence that we have to know the structure of our planetary system. And then this sets the stage then to understand why we've had through geological times so many impacts on the planet from these meteors. And then the segue from that is to recognize that the structure of Earth history, and the structure of geological time is actually formulated around the series of meteor impacts that have taken place. And the reason for that is that most of Earth history is broken up and structured according to the history of life and the paleontological fossil record of what we see on the planet. So this particular Earth structure, universal structure we've seen, then that's what allows that structural component of how time is carved up between primarily meteor impacts. [MUSIC]
