0:00:00.367,0:00:01.889 Hi, everybody. Welcome back. 0:00:01.890,0:00:03.449 Today we're covering the content 0:00:03.450,0:00:06.314 that is in Chapter 25[br]of your textbook, 0:00:06.314,0:00:10.170 and this chapter largely covers[br]some broad patterns 0:00:10.170,0:00:13.679 with regard to the history of life[br]on the planet. 0:00:13.679,0:00:16.806 When we were together last time,[br]we were looking at mechanisms 0:00:16.806,0:00:18.690 that could promote speciation,[br]right? 0:00:18.690,0:00:21.720 We talked[br]about allopatric speciation 0:00:21.720,0:00:24.333 and sympatric speciation. 0:00:24.333,0:00:25.629 Today, we're going to look at, 0:00:25.629,0:00:29.010 again, some broad-scale events[br]that occurred 0:00:29.010,0:00:31.370 over the history of life[br]on the planet 0:00:31.370,0:00:33.935 that include things[br]like mass extinctions, 0:00:33.935,0:00:37.895 and the phenomenon[br]of what we call adaptive radiation 0:00:37.895,0:00:41.973 where we see many,[br]many species 0:00:41.973,0:00:44.225 show up in-- in the fossil record. 0:00:44.225,0:00:47.138 And yeah, a lot of what we know[br]with regard to what 0:00:47.138,0:00:50.730 we're going to talk about today[br]comes from an exploration of 0:00:50.730,0:00:53.369 and interpretation[br]of that fossil record. 0:00:53.370,0:00:54.881 Starting[br]with this slide right here: 0:00:54.881,0:00:59.849 this is a amazing photo[br]of a skeleton of a whale 0:00:59.850,0:01:03.280 that was discovered[br]in the Sahara Desert. 0:01:03.280,0:01:05.540 So, you might be wondering,[br]well, how did that happen? 0:01:05.540,0:01:07.760 Researchers were--[br]were knowing where to look 0:01:07.760,0:01:11.662 when they were--[br]when they were trying to figure out 0:01:11.662,0:01:16.479 what are the origins[br]of marine mammals, for example. 0:01:16.479,0:01:20.447 And so, due to conversations[br]with geologists about, 0:01:20.447,0:01:23.156 you know,[br]where we might find fossils 0:01:23.156,0:01:27.998 of-- of particular creatures[br]from a particular time 0:01:27.998,0:01:29.980 in the history of life on Earth, 0:01:29.980,0:01:32.614 and other patterns of--[br]of events that-- 0:01:32.614,0:01:35.974 that led researchers to predict 0:01:35.974,0:01:38.750 that they[br]might actually find whale bones 0:01:38.750,0:01:40.959 in the--[br]in the desert of the Sahara. 0:01:40.959,0:01:42.293 And, in fact, they did. 0:01:42.293,0:01:46.110 So, that's just one example[br]of some of the work 0:01:46.110,0:01:48.749 that paleontologists do. 0:01:48.750,0:01:53.789 Paleontology is the study[br]of the fossil record. 0:01:53.790,0:01:56.609 So, yeah, let's go ahead[br]and get started 0:01:56.610,0:01:58.920 building on the work that--[br]that we have learned 0:01:58.920,0:02:01.328 from paleontologists today. 0:02:04.893,0:02:07.706 So, again, when we[br]use the word macroevolution 0:02:07.706,0:02:10.761 now we're really talking[br]about broad patterns of evolution 0:02:10.761,0:02:12.878 that--[br]that are above the species level. 0:02:12.878,0:02:15.117 So, we're looking at groups[br]of organisms. 0:02:15.117,0:02:19.532 And when we look in the fossil record,[br]we do see some trends. 0:02:19.532,0:02:21.352 You know, we see the emergence,[br]for example, 0:02:21.352,0:02:23.112 of terrestrial vertebrates. 0:02:23.112,0:02:25.615 We see the emergence[br]of other groups of species as well, 0:02:25.615,0:02:27.257 that I'm going to share[br]with you today. 0:02:27.257,0:02:30.553 We also see[br]that mass extinctions occurred. 0:02:30.553,0:02:31.982 And then there's been, you know, 0:02:31.982,0:02:34.436 there's been... 0:02:34.436,0:02:35.836 you know, that has affected 0:02:35.836,0:02:39.360 the evolutionary trajectory[br]of other species. 0:02:39.360,0:02:41.158 So, we'll talk about that today. 0:02:41.158,0:02:43.704 And then we'll focus[br]on some key adaptations 0:02:43.704,0:02:45.149 such as flight, for example. 0:02:45.149,0:02:47.428 So, when these new adaptations[br]arise, 0:02:47.428,0:02:50.650 it allows for what we[br]call "adaptive radiation". 0:02:50.650,0:02:52.702 I'll talk about that today[br]as well. 0:02:52.702,0:02:56.972 The possibility[br]for many new species 0:02:56.972,0:03:01.773 to emerge[br]over a relatively short period of time, 0:03:01.773,0:03:03.300 and I'm talking geologic time. 0:03:03.300,0:03:06.073 So, you know, short is relative here[br]in this conversation today. 0:03:06.073,0:03:11.351 But, yeah, when you[br]have a novel character that arises, 0:03:11.351,0:03:13.200 such as the ability to fly, 0:03:13.200,0:03:15.320 that promotes the possibility 0:03:15.320,0:03:18.023 for the-- 0:03:18.023,0:03:21.239 for a species[br]that has that particular character 0:03:21.239,0:03:24.980 to diverge into many other species 0:03:24.980,0:03:28.875 as they occupy new habitats[br]that are available to them 0:03:28.875,0:03:31.104 because of that character[br]that emerged. 0:03:31.104,0:03:35.320 So, yeah, we'll talk about each[br]of these in detail today. 0:03:37.747,0:03:39.574 All right,[br]if we're going to have a conversation 0:03:39.574,0:03:41.241 about the history of life[br]on Earth, 0:03:41.241,0:03:43.881 we might as well start[br]at the very beginning. 0:03:43.881,0:03:46.718 So--[br]So, one of our big questions is 0:03:46.718,0:03:48.338 what is the origin of life? 0:03:48.338,0:03:51.311 How did life ever get started[br]on planet Earth, right? 0:03:51.311,0:03:55.931 And so, I'm going to share[br]with you some evidence 0:03:55.931,0:03:57.939 that supports the idea 0:03:57.939,0:04:01.552 that the origin of life 0:04:01.552,0:04:04.118 occurred[br]via these sequential steps 0:04:04.118,0:04:05.557 that you see in my slide here. 0:04:05.557,0:04:07.575 So, it makes the most sense to us, 0:04:07.575,0:04:09.653 and the data support this idea, 0:04:09.653,0:04:11.659 that the first thing[br]that probably happened 0:04:11.659,0:04:14.718 was number one here,[br]abiotic synthesis. 0:04:14.718,0:04:17.959 Abiotic meaning non-living, right? 0:04:17.959,0:04:22.454 Abiotic synthesis[br]of very small organic molecules, 0:04:22.454,0:04:24.694 probably monomers of molecules. 0:04:24.694,0:04:26.643 And then, finally, polymers. 0:04:26.643,0:04:28.414 The joining of those together 0:04:28.414,0:04:31.683 to make those polymers[br]probably occurred. 0:04:31.683,0:04:36.163 And then, at some point, those-- 0:04:36.163,0:04:40.805 those molecules[br]were probably captured inside 0:04:40.805,0:04:44.588 what we colloquially[br]call, "protocells," right. 0:04:44.588,0:04:48.616 Proto- meaning first, these--[br]these precursors to modern cells. 0:04:48.616,0:04:51.149 And then lastly, 0:04:51.149,0:04:54.418 there is evidence[br]to suggest the origin 0:04:54.418,0:04:57.880 of self-replicating molecules, 0:04:57.880,0:04:59.534 similar to what we see today,[br]right? 0:04:59.534,0:05:03.506 Self-replicating DNA and RNA. 0:05:03.506,0:05:05.286 All right, let's take a look[br]at each one of these 0:05:05.286,0:05:07.433 in detail today. 0:05:09.460,0:05:11.691 So, one of the first things[br]that would have to happen, 0:05:11.691,0:05:13.527 according to[br]that sequence of events 0:05:13.527,0:05:14.959 that I shared with you previously 0:05:14.959,0:05:17.501 is the abiotic synthesis 0:05:17.501,0:05:20.994 of organic molecules. 0:05:20.994,0:05:25.624 And researchers[br]in the 1950s were curious 0:05:25.624,0:05:29.052 if that--[br]if they could get that to occur. 0:05:29.052,0:05:32.700 and, you know, like, the conversations[br]at the time were 0:05:32.700,0:05:37.169 well, what[br]did planet Earth's atmosphere 0:05:37.170,0:05:39.321 look like at the time? 0:05:39.321,0:05:40.320 Let me back up a minute. 0:05:40.320,0:05:44.059 We think that the planet formed[br]about 4.6 billion years ago, 0:05:44.059,0:05:46.619 but for[br]that first half a billion years, 0:05:46.619,0:05:50.548 so from 4.6 billion years ago[br]to 4 billion years ago 0:05:50.548,0:05:53.412 the planet[br]was probably not conducive 0:05:53.412,0:05:56.183 to life ever forming[br]on the planet. 0:05:56.183,0:05:58.380 There was--[br]it was constantly being bombarded 0:05:58.380,0:06:03.150 by rocks and debris,[br]and it was a very hot environment. 0:06:03.150,0:06:05.909 But about 4 point-- billion years ago, 0:06:05.910,0:06:08.249 4 billion years ago, 0:06:08.249,0:06:11.329 the planet cooled off,[br]the seas formed, 0:06:11.329,0:06:15.247 and the environment was-- 0:06:15.247,0:06:18.044 the atmosphere, we don't know[br]exactly what it looked like, 0:06:18.044,0:06:21.809 but we have some indication 0:06:21.809,0:06:25.841 that there was methane[br]in the atmosphere, 0:06:25.841,0:06:27.855 and there was ammonia[br]in the atmosphere, 0:06:27.855,0:06:30.602 and there's hydrogen gas[br]in the atmosphere. 0:06:30.602,0:06:34.299 And, whether or not it[br]was a-- a reducing environment 0:06:34.299,0:06:37.200 or an oxidizing environment. 0:06:37.200,0:06:39.505 Not sure. 0:06:39.505,0:06:41.868 That refers to whether-- 0:06:41.868,0:06:45.989 you know, today we're living[br]in an oxidizing atmosphere, right? 0:06:45.989,0:06:50.700 There's oxygen gas in our atmosphere[br]that will readily oxidize 0:06:50.700,0:06:52.124 other compounds, right-- 0:06:52.124,0:06:54.867 steal electrons away from--[br]from other compounds. 0:06:54.867,0:06:57.460 There was some indication recently 0:06:57.460,0:06:59.929 that the environment was,[br]in contrast to that, 0:06:59.929,0:07:03.827 a reducing environment full--[br]full of hydrogen gas, 0:07:03.827,0:07:05.485 like you see here, H2, 0:07:05.485,0:07:07.678 that would donate electrons[br]to compounds. 0:07:07.678,0:07:10.881 So, regardless of that, 0:07:10.881,0:07:13.605 this experiment right here[br]shows you an apparatus 0:07:13.605,0:07:16.289 that was set up by a grad student 0:07:16.290,0:07:18.719 from the University of Chicago[br]in 1953. 0:07:18.720,0:07:20.159 His name was Stanley Miller. 0:07:20.160,0:07:24.479 He and his--[br]his advisor worked on this project 0:07:24.480,0:07:28.200 where they--[br]they attempted to simulate 0:07:28.200,0:07:32.635 what they thought was the atmospheric[br]and oceanic conditions 0:07:32.635,0:07:36.339 on the planet 4 billion years ago, 0:07:36.339,0:07:40.243 to see if they could[br]get the abiotic synthesis 0:07:40.243,0:07:41.850 of organic molecules. 0:07:41.850,0:07:43.938 So, what you see in this apparatus 0:07:43.938,0:07:45.904 is a container 0:07:45.904,0:07:50.649 that might simulate the ocean. 0:07:50.649,0:07:54.648 And, you know, we know[br]from volcanic activity in the ocean 0:07:54.648,0:07:57.656 that there are areas where it's--[br]it's very hot. 0:07:57.656,0:07:59.381 So, they-- they simulated that, 0:07:59.381,0:08:02.696 you know,[br]providing thermal energy. 0:08:02.696,0:08:04.618 And then, you know,[br]some of that water 0:08:04.618,0:08:06.745 would, of course, evaporate. 0:08:06.745,0:08:09.020 And this part[br]of the chamber, here, 0:08:09.020,0:08:10.840 is kind of representing 0:08:10.840,0:08:12.587 what we think[br]were atmospheric conditions. 0:08:12.587,0:08:16.266 Here's methane, here's ammonia,[br]here's hydrogen gas. 0:08:16.266,0:08:21.443 He simulated lightning 0:08:21.443,0:08:23.312 with these electrodes here, 0:08:23.312,0:08:25.268 again, providing energy. 0:08:25.268,0:08:27.528 And then,[br]as that water vapor cooled-- 0:08:27.528,0:08:29.197 here's a condenser here. 0:08:29.197,0:08:32.273 input cold--[br]cold water to cool it off 0:08:32.273,0:08:34.963 to simulate[br]a cooler atmosphere. 0:08:34.963,0:08:36.661 And then as that water condensed, 0:08:36.661,0:08:39.237 he sampled it from time to time. 0:08:39.237,0:08:42.377 And, honestly,[br]his graduate advisor 0:08:42.377,0:08:45.336 actually thought[br]that there was no way that they 0:08:45.336,0:08:49.486 were going to get any kind[br]of organic monomers anytime soon. 0:08:49.486,0:08:50.984 You know, we thought that,[br]you know, 0:08:50.984,0:08:54.376 if this happened[br]on the planet 4 billion years ago, 0:08:54.376,0:08:56.228 how many million years did it take 0:08:56.228,0:09:00.081 to get synthesis[br]of these organic molecules? 0:09:00.081,0:09:02.541 But, lo and behold,[br]they actually got results 0:09:02.541,0:09:04.240 in a matter of months. 0:09:04.240,0:09:06.170 Three or four months later, 0:09:06.170,0:09:07.900 they found in their sample, 0:09:07.900,0:09:10.770 when they sampled it[br]for chemical analysis, 0:09:10.770,0:09:14.160 they found amino acids,[br]amazingly enough. 0:09:14.160,0:09:17.580 So, this did represent, 0:09:17.580,0:09:21.960 you know, the phenomenon[br]that abiotic synthesis 0:09:21.960,0:09:25.470 of organic molecules[br]can indeed occur. 0:09:25.470,0:09:27.030 This was an exciting moment 0:09:27.030,0:09:31.740 because it set the stage for-- 0:09:31.740,0:09:33.450 you know,[br]it set the stage chemically 0:09:33.450,0:09:36.274 for the conditions for life. 0:09:38.430,0:09:40.960 Another burning question,[br]so to speak, 0:09:40.960,0:09:45.749 that we have is, well,[br]where did life originate on the planet? 0:09:45.749,0:09:50.284 A lot of interested--[br]a lot of interest is being paid 0:09:50.284,0:09:54.060 to these alkaline vents[br]that are in the deep sea. 0:09:54.060,0:09:57.199 Here's a picture of one of these vents[br]in the slide here. 0:09:57.200,0:10:00.649 These vents release water[br]with a very high pH; 0:10:00.650,0:10:03.159 9, 10, 11. 0:10:03.160,0:10:05.379 So, they're considered[br]alkaline vents. 0:10:05.380,0:10:08.799 And also very warm water,[br]40 to 90 degrees C. 0:10:08.800,0:10:10.629 And the conditions in these vents 0:10:10.630,0:10:13.419 were probably very likely suitable 0:10:13.420,0:10:16.359 for the formation of some[br]of these organic compounds. 0:10:16.360,0:10:19.659 And, indeed,[br]researchers have looked at the surface 0:10:19.660,0:10:22.239 of the structures[br]that formed these vents 0:10:22.240,0:10:25.929 and found organic molecules attached[br]to those vents. 0:10:25.930,0:10:29.109 So, maybe this[br]is where life arose. 0:10:29.110,0:10:32.679 Other people are very interested[br]in looking at meteorites. 0:10:32.680,0:10:36.579 Meteorites may have been[br]another source of organic molecules. 0:10:36.580,0:10:38.889 For example,[br]the fragments of a meteorite 0:10:38.890,0:10:40.809 called the Murchison meteorite, 0:10:40.810,0:10:43.719 has been discovered[br]to contain more than 80 amino acids 0:10:43.720,0:10:45.339 and other key organic molecules, 0:10:45.340,0:10:49.239 including lipids, some sugars,[br]also some nitrogenous bases. 0:10:49.240,0:10:53.379 So, maybe these are the--[br]maybe we can-- 0:10:53.380,0:10:55.689 maybe we can consider that that is 0:10:55.690,0:10:58.329 where we got[br]these first organic molecules 0:10:58.330,0:11:03.320 is from the meteorites[br]that have bombarded the planet.