1 00:00:00,154 --> 00:00:03,628 We left off in the last video in the Archean eon, 2 00:00:03,704 --> 00:00:07,091 where Arche comes from ancient Greek, meaning beginning or origin, 3 00:00:07,091 --> 00:00:11,765 and it's the eon in which either life first starts to exist, 4 00:00:11,765 --> 00:00:13,929 or at least it's first starts to somewhat flourish, 5 00:00:13,929 --> 00:00:17,034 it's possible that maybe life starts to exist 6 00:00:17,034 --> 00:00:18,813 at the end of the Hadean eon 7 00:00:18,813 --> 00:00:21,169 and of course, this boundary is big. 8 00:00:21,169 --> 00:00:23,239 The Archeon is also the first eon 9 00:00:23,239 --> 00:00:26,523 where we still have rocks from that time. 10 00:00:26,523 --> 00:00:29,851 So we are able to find rocks that we can date to be roughly 11 00:00:29,851 --> 00:00:33,574 3,8 biliion years. The other really interesting thing 12 00:00:33,574 --> 00:00:37,365 that happened in the Archeon eon that really has a profound 13 00:00:37,365 --> 00:00:40,521 effects once we get to the Proteozoic eon 14 00:00:40,521 --> 00:00:44,395 is that you start to have cyanobacteria 15 00:00:44,395 --> 00:00:47,503 to produce oxygen. We've seen in the last video 16 00:00:47,503 --> 00:00:50,707 that they were producing oxygen but most of that oxygen 17 00:00:50,707 --> 00:00:53,346 was being absorbed by iron in the oceans. 18 00:00:53,346 --> 00:00:57,359 But what happens as we enter into the Proteozoic eon, 19 00:00:57,359 --> 00:01:01,836 Proteozoic eon, it's right over here as you can see 20 00:01:01,836 --> 00:01:05,676 we write it Pro-teo-zoic, 21 00:01:05,676 --> 00:01:08,904 we are now in the Proteozoic eon. 22 00:01:08,904 --> 00:01:15,655 That starts up about 2,5 billion years ago 23 00:01:15,655 --> 00:01:17,842 and Proteotoic comes from the Greek 24 00:01:17,842 --> 00:01:22,714 for earlier life. 25 00:01:22,714 --> 00:01:25,183 I'm not a Greek scholar, so you know, 26 00:01:25,183 --> 00:01:29,108 forgive me if I'm not getting the translation exactly right. 27 00:01:29,108 --> 00:01:33,039 But what's really interesting about the Proteozoic eon 28 00:01:33,039 --> 00:01:37,163 is that that oxygen that was being produced by that cyanobacteria 29 00:01:37,163 --> 00:01:40,901 at some point begins to saturate the iron 30 00:01:40,901 --> 00:01:43,917 and any other molecule that could have absorbed before. 31 00:01:43,917 --> 00:01:48,706 And once it is saturated, it starts to get released into the atmosphere. 32 00:01:48,706 --> 00:01:51,577 So the oxygen starts to get released 33 00:01:51,577 --> 00:01:54,664 and accumulated in the atmosphere. We think this happened 34 00:01:54,664 --> 00:01:58,430 to start to happend about 2,4 biliion years ago. 35 00:01:58,430 --> 00:02:01,945 So 2,4 biliion years ago 36 00:02:01,945 --> 00:02:05,402 oxygen begins to accumulate in the atmosphere. And of course, you know 37 00:02:05,402 --> 00:02:08,264 these days they may have been moved around a few hundred milion years 38 00:02:08,264 --> 00:02:11,492 as it gets more and more detailed. But this is the current understanding 39 00:02:11,492 --> 00:02:15,514 of when things happened. Maybe we will look at the geological records 40 00:02:15,514 --> 00:02:17,875 and fossil records that will move things around in the future. 41 00:02:17,875 --> 00:02:21,242 I can only imagine that 50 years from now or 100 years from now 42 00:02:21,242 --> 00:02:23,906 somenes still watching this video and lot of these might say 43 00:02:23,906 --> 00:02:27,455 hey, now we have found later that oxygen started to accumulate in the atmosphere 44 00:02:27,455 --> 00:02:30,491 earlier or later or that Eucaryotes occured earlier or later, 45 00:02:30,491 --> 00:02:33,991 but this, as far as I can tell, is our best current understanding. 46 00:02:33,991 --> 00:02:42,101 2,4 biliion years ago oxygen begins to accumulate 47 00:02:42,101 --> 00:02:47,088 in the atmosphere. And what is interesting 48 00:02:47,088 --> 00:02:50,171 about this is once it accumulates, once it has come 49 00:02:50,171 --> 00:02:53,642 critical amount of oxygen in the atmosphere, 50 00:02:53,642 --> 00:02:57,623 and I touched on this in the last video, about 2,3 biliion years ago 51 00:02:57,623 --> 00:03:01,498 we have something called the great oxygenation event. 52 00:03:01,498 --> 00:03:06,527 Sometimens called the oxygen catastrophy. And this is right here, 53 00:03:06,527 --> 00:03:09,467 2,3 billion years ago or 23 hundred milion years ago 54 00:03:09,467 --> 00:03:14,106 the atmosphere becomes oxygen-rich. 55 00:03:14,106 --> 00:03:16,617 Not as rich as our current atmosphere, 56 00:03:16,617 --> 00:03:21,656 But it becomes oxygen-rich enough that at least the environment 57 00:03:21,656 --> 00:03:25,660 becomes suitable for eucaryotic organisms 58 00:03:25,660 --> 00:03:29,627 or eucaryotic cell. Now, the other interesting thing that we might not care 59 00:03:29,627 --> 00:03:33,038 so much about it because we needed the oxygen, is that we think that 60 00:03:33,038 --> 00:03:36,614 this was actually the greatest extinction event in the history of Earth. 61 00:03:36,614 --> 00:03:40,037 That's what is called the oxygen catastrophy. 62 00:03:40,037 --> 00:03:43,827 So right over here, 2,3 billion years ago, a shouldn't giggle about this, 63 00:03:43,827 --> 00:03:46,773 this is a serious matter, this it the greatest, 64 00:03:46,773 --> 00:03:50,184 the greatest extinction event 65 00:03:50,184 --> 00:03:55,702 in Earth's history! 66 00:03:55,702 --> 00:03:59,770 In History. And I'll do history with capital H. 67 00:03:59,770 --> 00:04:02,527 In the history of the Earth. And that's because of 68 00:04:02,527 --> 00:04:07,199 the cyanobacteria producing lots of oxygen, eventually saturates the iron 69 00:04:07,199 --> 00:04:10,574 it accumulates in the air, once it gets to enough concentration 70 00:04:10,574 --> 00:04:12,909 it begins to actually suffocate. It's poisonous 71 00:04:12,909 --> 00:04:16,998 to most of the other organisms on the planet 72 00:04:16,998 --> 00:04:20,169 that were anaerobic, that they did not need oxygen, 73 00:04:20,169 --> 00:04:24,001 they actually found oxygen poisonous. 74 00:04:24,001 --> 00:04:28,780 Now, but since we have oxygen there's two interesting things that happened 75 00:04:28,780 --> 00:04:31,303 once that oxygen accumulated did other than causing this 76 00:04:31,303 --> 00:04:34,424 that mass extinction. There are actually three interesting things. Two of them 77 00:04:34,424 --> 00:04:38,741 are essentially crucial to us eventually showing up 78 00:04:38,741 --> 00:04:41,296 on this planet. The first is that it becames 79 00:04:41,296 --> 00:04:45,328 suitable now for Eucaryotes to exists. 80 00:04:45,328 --> 00:04:49,250 Eucaryotic organisms. Remember, these are organisms that have 81 00:04:49,250 --> 00:04:53,373 the nuclear membranes around their DNA, most Eucaryotes have other 82 00:04:53,373 --> 00:04:57,590 organelles like mitochontria. They need oxygen. 83 00:04:57,590 --> 00:05:02,920 They need oxygen. 84 00:05:02,920 --> 00:05:05,752 You can go to the biology play there we actually talk about respiration 85 00:05:05,752 --> 00:05:08,922 that occures in the mitochondria and that is obviously 86 00:05:08,922 --> 00:05:12,255 a process that needs oxygen. So when we have 87 00:05:12,255 --> 00:05:15,314 oxygen in the atmosphere we're starting to have 88 00:05:15,314 --> 00:05:18,129 an environment where Eucaryotes could at least exist 89 00:05:18,129 --> 00:05:21,580 and based on the fossil records on what we looked the DNA has changed 90 00:05:21,580 --> 00:05:24,675 over time, I'll do more videos on that, we think that 91 00:05:24,675 --> 00:05:28,383 the first Eucaryotes showed up about 92 00:05:28,383 --> 00:05:31,743 2,2 billion years ago, althought there is some debate here, 93 00:05:31,743 --> 00:05:35,006 there is some evidence that it might have been a little earlier, a little later, 94 00:05:35,006 --> 00:05:38,665 I'm sure that number will be refind. But, you know, 95 00:05:38,665 --> 00:05:41,583 give a take of few hundred million of years, 96 00:05:41,583 --> 00:05:45,823 one procaryot got engulfed by another procaryot 97 00:05:45,823 --> 00:05:47,770 and say 'hey, we do pretty well living together' 98 00:05:47,770 --> 00:05:51,526 lot of the current theories that mitochondria has actually descended 99 00:05:51,526 --> 00:05:56,619 the current theory is that mitochondria actually descended from 100 00:05:56,619 --> 00:06:00,323 kind of an ancient procaryotic cell, an ancient bactery actually has 101 00:06:00,323 --> 00:06:04,042 its own DNA. Actually your mitochondrial DNA 102 00:06:04,042 --> 00:06:06,420 is passed down from your mother and your mother's mother 103 00:06:06,420 --> 00:06:09,408 and your grandmother's mother and so on. It's kind of another 104 00:06:09,408 --> 00:06:12,605 little animal living inside of a larger cell. 105 00:06:12,605 --> 00:06:15,910 And we are Eucaryotes. We needed this to happen. 106 00:06:15,910 --> 00:06:20,483 The human body is not one eucaryotic cell. We're made up of trillions. 107 00:06:20,483 --> 00:06:24,409 It is estimated to 50 to 100 trillion eucaryotic cells. 108 00:06:24,409 --> 00:06:28,182 So these are our ancestors that had to 109 00:06:28,182 --> 00:06:31,076 come into being at that time. Once again, all of this 110 00:06:31,076 --> 00:06:34,375 is happening inside of the oceans. 111 00:06:34,375 --> 00:06:38,703 The other interesting thing that happened. Remember, we were being bombarded 112 00:06:38,703 --> 00:06:41,744 with UV radiation from the sun. So if you are on the land, 113 00:06:41,744 --> 00:06:46,591 let me draw the land and the ocean. 114 00:06:46,591 --> 00:06:51,171 So here is the ocean and here is the land. 115 00:06:51,171 --> 00:06:54,791 Here is the land righ over there in yellow. 116 00:06:54,791 --> 00:06:58,739 Constantly being bombarded with UV radiation. 117 00:06:58,739 --> 00:07:02,853 UV stand for ultraviolet. It is even more violet than purple. 118 00:07:02,853 --> 00:07:07,206 So it is constantly being bombarded with ultraviolet radiation 119 00:07:07,206 --> 00:07:11,153 from the sun which is very inhospitable to DNA 120 00:07:11,153 --> 00:07:14,980 and to life. So the only life at this point could occure 121 00:07:14,980 --> 00:07:18,748 in the ocean where was protected to some degree from the UV, 122 00:07:18,748 --> 00:07:22,603 the land was just open to it. 123 00:07:22,603 --> 00:07:24,855 Anything on the land was just irradiated. 124 00:07:24,855 --> 00:07:28,840 The DNA would get mutated, just would not be able to live. 125 00:07:28,840 --> 00:07:32,242 So what I guess had to happen, and the reason why 126 00:07:32,242 --> 00:07:35,348 are we are able to live on the land, is that we have an ozone layer. 127 00:07:35,348 --> 00:07:40,862 We have an ozone layer up in the upper atmosphere 128 00:07:40,862 --> 00:07:43,834 that helps absorb, that blocks 129 00:07:43,834 --> 00:07:47,321 most of the UV radiation from the sun. 130 00:07:47,321 --> 00:07:51,740 And now the oxygen began to accumulate. We had the oxygen catastrophy, 131 00:07:51,740 --> 00:07:56,975 oxygen accumulates in the atmosphere, some of that oxygen 132 00:07:56,975 --> 00:07:59,571 goes into the the upper atmosphere. So we are now in this time period. 133 00:07:59,571 --> 00:08:03,910 It goes into the upper atmosphere, it actually reacts with the UV light 134 00:08:03,910 --> 00:08:07,106 to turn into ozone which then can help 135 00:08:07,106 --> 00:08:09,945 actually block the UV ligt. I'll do another video 136 00:08:09,945 --> 00:08:14,670 on the ozone-oxygen cycle. So this oxygen production 137 00:08:14,670 --> 00:08:17,873 is crucial one to have an ozone layer, 138 00:08:17,873 --> 00:08:21,303 so that eventually life can exist on the land, 139 00:08:21,303 --> 00:08:25,702 it is also crucial because eucaryotic organisms need that oxygen. 140 00:08:25,702 --> 00:08:29,005 Now the third thing that happened and also being a significant event, 141 00:08:29,005 --> 00:08:34,512 we believe that that oxygen that started to accumulate in the atmosphere 142 00:08:34,512 --> 00:08:38,412 reacted with methane in the atmosphere, 143 00:08:38,412 --> 00:08:46,238 and methane is a greenhouse gas. It helps retain heat 144 00:08:46,238 --> 00:08:49,712 in the atmosphere. And once it reacts with the oxygen 145 00:08:49,712 --> 00:08:53,169 and starts dropping out of the atmosphere as methane, we believe 146 00:08:53,169 --> 00:08:56,080 the Earth cooled down and it entered its first 147 00:08:56,080 --> 00:08:59,605 and some people believe its longest snowball period. 148 00:08:59,605 --> 00:09:03,332 So that's what they talk about here in this diagram. 149 00:09:03,332 --> 00:09:08,855 The first snowball Earth. It's sometimes called the Huronic glaciation. 150 00:09:08,855 --> 00:09:11,434 That happened because we were unable to retain the heat 151 00:09:11,434 --> 00:09:14,660 if that theory is correct. So as the theory goes, 152 00:09:14,660 --> 00:09:19,842 the whole Earth essentially just iced over. 153 00:09:19,842 --> 00:09:24,102 So as we go through the Proteozoic eon, 154 00:09:24,102 --> 00:09:28,309 I guess the big markers of that, this is the first time 155 00:09:28,309 --> 00:09:30,923 that we have an oxygen-rich atmosphere. 156 00:09:30,923 --> 00:09:35,169 The first time that Eucaryotes can come to existence 157 00:09:35,169 --> 00:09:40,155 because now they have oxygen, I guess we can say, to breath. 158 00:09:40,155 --> 00:09:43,433 The other big thing is that this is where the ozone forms. 159 00:09:43,433 --> 00:09:46,769 It kind of sets the stage for the next eon. 160 00:09:46,769 --> 00:09:50,704 For animals or for living things to eventually 161 00:09:50,704 --> 00:09:54,767 get on to the land. I will talk about that in the next video.