Today we want to talk about the origins of life. Where did life come from on planet Earth. And we're also going to spend some time talking about evolution, and classification of living organisms as well. We know a lot about early Earth based on geology, and it was an unpleasant place from, at least the way we understand life now, from the point of view of life. It was, we refer to this period as prebiotic or sterile. It was a really hot Earth, it was volcanic. There were asteroids hitting it regularly. There was volcanoes, there were electrical storms and dust storms, really just an unpleasant place overall. So the earth is probably about 5 billion years old, you know, give or take. It's probably a little bit less than that. Life has been around for about three and a half billion of those years and it depends on how you measure it, but that's a fairly reasonable consensus. So you can figure about a billion years after the beginning of Earth is when the first evidence of life shows up. Now large macroscopic plants and animals and when I refer to macroscopic, I mean things that are big enough that you don't need a microscope to see them. Those have only been around for about 900 million years, and large animals like the dinosaurs, this you know, these we think of dinosaurs is sort of ancient Earth history, but actually, they're fairly recent in both the history of earth and the history of life on Earth. Humans have been around for just a blink, about a couple hundred thousand years possibly. We refer to these conditions on early Earth is the primordial soup. We know a lot about the chemicals that were present on early Earth, molecules like iron sulfide, hydrogen sulfide, carbon dioxide, potassium, cyanide, carbon monoxide, ammonia. These molecules were present in abundance. And somehow these molecules along with the conditions on early Earth, as shown here in the directions somehow provided the exact right set of conditions for the beginnings of highly organized, complex life, which is really, even a single cell, falls into that category. Somehow those these molecules became biological molecules and then organized into living things. And scientists have been really working hard to try to understand how this might have happened. And one of the very first experiments that was done in 1952 by Miller and Urey and what they did is in a flask, so the here's their organic chemistry set up and they've got a flask and they've added some of these chemicals that we were talking about. Things like methane, hydrogen, ammonia water, and they exposed these chemicals. two conditions similar to early Earth. So they had electrical sparks to simulate lightning. They had temperatures that were similar to early Earth. And at the end of a week, when they looked at the molecules that were formed, more than 10 to 15% of the carbon that had been in the flask was converted to the kinds of organic molecules we associate with life. And it turns out that since Miller's death in 2007, they've actually gone back and looked at the vials from his original experiments and they re-analyzed them and they found more than 20 different amino acids. In other similar experiments to the original Miller Yuri experiments have yielded nucleotides, which are the components of DNA and RNA. So this isn't necessarily how it happened. But it certainly supports the idea that life at least the molecules we associate with life, could have formed under the conditions that were present on early Earth. All right. The next video I'm going to show you is about RNA. So one of the major hypotheses that people have put forward about how these biological molecules assembled into life starts with a molecule called ribonucleic acid. So I'm going to have you watch this video next and then we'll come back.