Timeline of Life on Earth

by Jason Amores Sumpter
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Now let's take a quick look and I really mean brief Look at the course of life on Earth. Now the different time periods of Earth's history have been divided into various subsections. And here in this diagram, you can see that we have these various subsections Haiti In our key in, uh, pro tears OIC Haley is OIC, Mesozoic Santa's OIC. But I'm actually just gonna make to big divisions in the course of Earth's history what I'm going, what is called pre Cambrian time and the Finnair's OIC era, which is the modern era in which we live now. Pre Cambrian time is the period of time between the formation of Earth and the appearance of most animal groups around the Cambrian explosion, which was a period of rapid, rapid evolutionary diversification. Now, during the majority of Earth's history, life has been Eunice Cellular. In fact, you can see from this figure multi cellular life is quite recent. In terms off the billions of years three earth has existed. Also very important thing to note, especially about the early ages of Earth's history, said Oxygen was absent. In fact, it wasn't until the photosynthetic process processes evolved that oxygen became abundant in the atmosphere and in fact, way back in time of the dinosaurs. For example, oxygen was farm or abundant than it is now, which is part of the reason that living organisms were so much bigger back then. It's in part because of the lower oxygen concentrations that life has gotten smaller over the over the course of history since the dinosaurs, until now, now very important event occurred in pre Cambrian time. That is the formation of the first you Kerasiotes and they were formed through a process called Sim Biogenesis. What is sin Biogenesis Sim biogenesis which you probably know is Endo Symbian Theory is when two separate life forms fused together to create a new life forms. So what is Endo Symbian theory will remember We had our big, um, big giant member in a cell that engulfed itty bitty little pro carry out, which eventually became the mitochondria. That was a sim biogenesis event. So the first you Kerasiotes formed through sim biogenesis through one cell engulfing another and the two living symbiotically Um additionally, multi cellular organisms appeared during this time another really important development in the course of life on earth. Now, in the Fanara Zoe area, we've had a couple pretty major events in the Paleozoic era. We have the Cambrian explosion, which again kind of defines the boundary between pre Cambrian time and this modern era that we live in. Um, so the Cambrian explosion created a great diversity of life. Also, during the Paleozoic era, we have the terrestrial ization of plants and animals. Yes, before this time, all life existed in the oceans and it was in this era where life actually finally made it toe land first plants and animals. Then in the Mesozoic era, we have the dominance of Gim No sperms and dinosaurs give no sperms are plant organisms like pine trees, for example, Um, these were the dominant plant life form on terrestrial earth back then, and dinosaurs were the dominant animal life form on terrestrial earth. Back then, of course, we had a great or a mass extinction. See you later. Dinosaurs and we move into the Seine is OIC era where now the plant scene is dominated by angiosperms, which are flowering plants like the ones that produce delicious fruits and vegetables that we so love to eat and also the dominance of mammals in the animal scene and not to get too deep into it. But in many ways, the dying out of the dinosaurs opened the door for mammals to become the next dominant animal form. So again, those mass extinctions, it's kind of like one door closes, another door opens Now. The last idea I want to touch upon in this lesson is the idea of punctuated equilibrium. And this is essentially the theory that evolutionary changes occur rapidly, like in the Cambrian explosion. And these rapid, thes events, where there's rapid evolutionary change punctuate long periods of very little change. So basically, if you were to plot the course of evolutionary change on Earth, you'd have long periods were not a lots going on and then boom, spikes of activity and then again, long periods of not a lot going on. And then some major thing causes boom, another burst of activity. So Cambrian Explosion is an example of one of those bursts. But the creation of you Kerasiotes represents another example of that punctuated rapid change, right. We have some biogenesis new life is created and boom, it just explodes and takes off into all these different shapes and forms. So, yes, Thecornerscores of Earth's history is not just a steady progression with steady change but in fact, more chaotic, You know, periods of rest with periods of evolutionary explosive chaos. Basically. All right, that's all I have for this lesson. I'll see you guys next time.