1 00:00:00,761 --> 00:00:03,640 The earth is now starting to get closer 2 00:00:03,640 --> 00:00:08,369 to being hospitable to people or animals like us 3 00:00:08,369 --> 00:00:10,706 In the last video we saw, during the 4 00:00:10,706 --> 00:00:15,076 Proterozoic eon, oxygen began to accumulate 5 00:00:15,076 --> 00:00:16,432 in the atmosphere. 6 00:00:16,432 --> 00:00:18,178 This actually caused this first snowball earth 7 00:00:18,178 --> 00:00:21,639 and this mass extinction of all the anaerobic species 8 00:00:21,639 --> 00:00:25,131 that made conditions suitable for eukaryotic cells 9 00:00:25,131 --> 00:00:26,660 and maybe even more important, 10 00:00:26,660 --> 00:00:28,675 these eukaryotic cells were able to form 11 00:00:28,675 --> 00:00:32,014 multicellular organisms, and we see where that starts 12 00:00:32,014 --> 00:00:35,258 right here on this chart. 13 00:00:35,258 --> 00:00:38,130 Multicellular life starts right over here. 14 00:00:38,130 --> 00:00:40,521 And I want to be clear, all of these things are moving targets 15 00:00:40,521 --> 00:00:42,333 as we discover more things in the geological 16 00:00:42,333 --> 00:00:44,711 record and we get more tools at our disposal 17 00:00:44,711 --> 00:00:46,150 these numbers get tweaked. 18 00:00:46,150 --> 00:00:47,486 But they do give you a good sense, 19 00:00:47,486 --> 00:00:49,358 based on our current understanding 20 00:00:49,358 --> 00:00:52,143 of when these things start to appear. 21 00:00:52,143 --> 00:00:53,731 And coinciding with multicellular 22 00:00:53,731 --> 00:00:55,533 life, and this is interesting in its own right 23 00:00:55,533 --> 00:00:59,169 because it has its own meta-level effect on evolution, 24 00:00:59,169 --> 00:01:07,288 you actually start also having sexual reproduction. 25 00:01:07,288 --> 00:01:08,850 And what's interesting about this, 26 00:01:08,850 --> 00:01:11,199 why this has such a big impact on evolution, 27 00:01:11,199 --> 00:01:13,618 we talk about it a lot in the biology playlist, 28 00:01:13,618 --> 00:01:17,897 is before evolution, variation in DNA had to be 29 00:01:17,897 --> 00:01:22,125 completely dependent on mutations and random movements 30 00:01:22,125 --> 00:01:24,411 within DNA and maybe some viruses. 31 00:01:24,411 --> 00:01:27,944 Now with sexual reproduction, you had 32 00:01:27,944 --> 00:01:30,712 a systematic mixing of DNA, 33 00:01:30,712 --> 00:01:32,730 so that you got more variation in the gene pool 34 00:01:32,730 --> 00:01:38,387 which allowed more selection, more variance to select for 35 00:01:38,387 --> 00:01:41,420 and so you kind of had an acceleration 36 00:01:41,420 --> 00:01:43,992 in the actual pace of evolution. 37 00:01:43,992 --> 00:01:47,688 We're talking, I've looked at a bunch of sources, 38 00:01:47,688 --> 00:01:50,230 they say from 1.2 billion, 1.5 billion, 39 00:01:50,230 --> 00:01:52,061 a little bit over a billion 40 00:01:52,061 --> 00:01:56,828 you start having these multicellular lifeforms 41 00:01:56,828 --> 00:01:59,106 and sexual reproduction. 42 00:01:59,106 --> 00:02:01,081 The other thing that we talked about from 43 00:02:01,081 --> 00:02:04,776 the Proterozoic eon, is the accumulation of oxygen 44 00:02:04,776 --> 00:02:06,952 allowed the ozone layer to build up. 45 00:02:06,952 --> 00:02:10,994 Ozone is just three oxygen atoms, it is O3. 46 00:02:10,994 --> 00:02:14,720 And by the end of the Proterozoic eon 47 00:02:14,720 --> 00:02:18,064 so we're talking about 550 million years ago 48 00:02:18,064 --> 00:02:22,306 (give or take a hundred million years) 49 00:02:22,306 --> 00:02:23,803 (these are all moving targets) 50 00:02:23,803 --> 00:02:26,742 the ozone layer was dense enough to protect 51 00:02:26,742 --> 00:02:28,697 the land from UV rays, we talked about that 52 00:02:28,697 --> 00:02:31,844 in the last video. 53 00:02:31,844 --> 00:02:34,303 The Earth is being bombarded with UV rays 54 00:02:34,303 --> 00:02:36,174 and the ozone layer is the only thing that 55 00:02:36,174 --> 00:02:39,899 keeps us from being seriously irradiated by the sun 56 00:02:39,899 --> 00:02:42,585 and allows land animals to actually live. 57 00:02:42,585 --> 00:02:45,138 And so coinciding with that time 58 00:02:45,138 --> 00:02:47,762 period, around 550 million years ago, 59 00:02:47,762 --> 00:02:50,413 you start to have life colonizing, 60 00:02:50,413 --> 00:02:53,697 especially significant life colonizing land. 61 00:02:53,697 --> 00:03:00,735 Life colonizes the land. 62 00:03:00,735 --> 00:03:03,023 And this was an interesting, when I first learned it, 63 00:03:03,023 --> 00:03:05,176 kind of an "Aha!" moment. 64 00:03:05,176 --> 00:03:09,753 You always assume that trees and grasses 65 00:03:09,753 --> 00:03:10,670 are part of the background, 66 00:03:10,670 --> 00:03:13,316 they come part and parcel with land, 67 00:03:13,316 --> 00:03:16,383 but it turns out that animals colonized land 68 00:03:16,383 --> 00:03:18,382 before plants did. 69 00:03:18,382 --> 00:03:21,319 Plants didn't come into the picture before about 70 00:03:21,319 --> 00:03:26,024 450 million years ago, give or take a few tens of 71 00:03:26,024 --> 00:03:27,710 millions of years. 72 00:03:27,710 --> 00:03:29,736 And so we're now entering the end of the 73 00:03:29,736 --> 00:03:32,062 Proterozoic eon. 74 00:03:32,062 --> 00:03:34,069 Life has started to colonize land, 75 00:03:34,069 --> 00:03:36,188 we now have an ozone layer, 76 00:03:36,188 --> 00:03:39,491 and actually there's another snowball glaciation 77 00:03:39,491 --> 00:03:41,860 or snowball earth near the end of the 78 00:03:41,860 --> 00:03:46,858 Proterozoic eon, and there are a bunch of theories 79 00:03:46,858 --> 00:03:49,339 about why it came about and why it disappeared 80 00:03:49,339 --> 00:03:50,621 maybe there were volcanoes 81 00:03:50,621 --> 00:03:53,430 greenhouse gases, who knows. 82 00:03:53,430 --> 00:03:55,260 But as we enter the end of that, 83 00:03:55,260 --> 00:03:57,507 we start seeing life begin to flourish. 84 00:03:57,507 --> 00:04:00,263 And it starts to really flourish as we enter 85 00:04:00,263 --> 00:04:03,574 the (I always have trouble saying this) 86 00:04:03,574 --> 00:04:06,374 Phanerozoic eon 87 00:04:06,374 --> 00:04:07,921 It's not even labelled here. 88 00:04:07,921 --> 00:04:13,025 The Phanerozoic eon is this chunk of time 89 00:04:13,025 --> 00:04:14,513 right over here, let me write it out. 90 00:04:14,513 --> 00:04:16,232 This right over here is the 91 00:04:16,232 --> 00:04:23,787 Phanerozoic eon. 92 00:04:23,787 --> 00:04:27,676 These divisions right here are eons 93 00:04:27,676 --> 00:04:32,111 and then they break into eras. 94 00:04:32,111 --> 00:04:34,174 Eras are subsets of eons. 95 00:04:34,174 --> 00:04:35,862 They're hundreds of millions of years. 96 00:04:35,862 --> 00:04:37,435 This is the Paleozoic era, 97 00:04:37,435 --> 00:04:40,259 the Mesozoic era and the Cenozoic era. 98 00:04:40,259 --> 00:04:43,008 And that's actually our current era. 99 00:04:43,008 --> 00:04:45,039 But perhaps the most interesting, 100 00:04:45,039 --> 00:04:46,296 I don't want to pick favorites here, 101 00:04:46,296 --> 00:04:48,536 but it's one of the most interesting times in the 102 00:04:48,536 --> 00:04:50,474 geologic era 103 00:04:50,474 --> 00:04:56,683 is the first period in the Paleozoic era, 104 00:04:56,683 --> 00:05:02,247 which is the first era in the Phanerozoic eon - 105 00:05:02,247 --> 00:05:04,584 and that's the Cambrian period. 106 00:05:04,584 --> 00:05:05,548 You might have heard of it before, 107 00:05:05,548 --> 00:05:11,575 that's about this period of time here. 108 00:05:11,575 --> 00:05:16,471 Cambrian. And during this period of 109 00:05:16,471 --> 00:05:19,527 time, the earth experiences what we call 110 00:05:19,527 --> 00:05:21,632 the Cambrian Explosion. That's because there 111 00:05:21,632 --> 00:05:27,079 was just this explosion in the number of species 112 00:05:27,079 --> 00:05:30,618 and genera that existed, the biodiversity 113 00:05:30,618 --> 00:05:31,750 on the planet. 114 00:05:31,750 --> 00:05:34,363 It might just be that we had the ozone layer protecting us, 115 00:05:34,363 --> 00:05:35,979 things were colonizing land, 116 00:05:35,979 --> 00:05:38,159 it was an oxygen rich environment. 117 00:05:38,159 --> 00:05:43,017 We start seeing complex multicellular organisms, 118 00:05:43,017 --> 00:05:44,970 it's about that time. 119 00:05:44,970 --> 00:05:47,311 If you fast forward maybe a few tens of millions of years, 120 00:05:47,311 --> 00:05:49,243 you start seeing the first fish, 121 00:05:49,243 --> 00:05:52,901 the first pre-amphibians or proto-amphibians. 122 00:05:52,901 --> 00:05:56,404 You fast forward a little bit as we get out of 123 00:05:56,404 --> 00:05:58,297 the Cambrian period, we start seeing 124 00:05:58,297 --> 00:06:05,255 plants, so they draw it right over here. 125 00:06:05,255 --> 00:06:06,885 And of course these are moving targets depending 126 00:06:06,885 --> 00:06:10,352 on what we discover in the fossil record. 127 00:06:10,352 --> 00:06:14,455 And for me, the big "Aha!" moment here is 128 00:06:14,455 --> 00:06:17,194 so many of these things you consider fundamental to 129 00:06:17,194 --> 00:06:21,594 what Earth is a relatively recent phenomenon. 130 00:06:21,594 --> 00:06:26,761 Plants weren't on land until about 450 million years ago. 131 00:06:26,761 --> 00:06:30,632 Insects weren't on land, or did not even exist 132 00:06:30,632 --> 00:06:33,512 until about 400 million years ago. 133 00:06:33,512 --> 00:06:36,399 Reptiles didn't exist until 300 million years ago. 134 00:06:36,399 --> 00:06:40,145 So we're about right over here now. 135 00:06:40,145 --> 00:06:42,793 Mammals didn't exist until 200 million years ago. 136 00:06:42,793 --> 00:06:46,255 Birds didn't exist until about 150 million years ago. 137 00:06:46,255 --> 00:06:47,961 The whole dinosaur age, which we consider 138 00:06:47,961 --> 00:06:53,627 in our distant past, that's essentially the Mesozoic era. 139 00:06:53,627 --> 00:06:56,792 So this is essentially the age of the dinosaurs. 140 00:06:56,792 --> 00:06:58,279 When you look at your time clock you see 141 00:06:58,279 --> 00:07:02,254 it's a relatively recent time period, 142 00:07:02,254 --> 00:07:05,129 and it actually ends with, we currently believe, 143 00:07:05,129 --> 00:07:09,685 a huge rock, a 6-mile diameter rock 144 00:07:09,685 --> 00:07:11,260 colliding with what is now 145 00:07:11,260 --> 00:07:14,652 the Yucatan Peninsula in Mexico, right off the coast 146 00:07:14,652 --> 00:07:15,793 of the Yucatan Peninsula. 147 00:07:15,793 --> 00:07:18,407 And it destroyed all of the large land lifeforms , 148 00:07:18,407 --> 00:07:20,825 especially the dinosaurs. 149 00:07:20,825 --> 00:07:23,147 And to put all of this in perspective, 150 00:07:23,147 --> 00:07:24,947 and actually the thing that really was an 151 00:07:24,947 --> 00:07:26,821 "Aha!" moment for me, 152 00:07:26,821 --> 00:07:29,773 plants are 450 million years ago, 153 00:07:29,773 --> 00:07:33,916 grass I view as this fundamental thing in nature, 154 00:07:33,916 --> 00:07:34,926 but grass has only been 155 00:07:34,926 --> 00:07:36,352 around for about 156 00:07:36,352 --> 00:07:39,172 (I've seen multiple estimates) 40-70 million years. 157 00:07:39,172 --> 00:07:43,073 Grass is a relatively new thing on the planet. 158 00:07:43,073 --> 00:07:46,386 Flowers have only been around for 130 million years. 159 00:07:46,386 --> 00:07:48,386 So there was a time when you had dinosaurs, 160 00:07:48,386 --> 00:07:49,916 but you did not have flowers 161 00:07:49,916 --> 00:07:52,623 and you did not have grass. 162 00:07:52,623 --> 00:07:54,729 And so you fast forward all the way, 163 00:07:54,729 --> 00:07:56,725 when you look at this scale it's funny to look at, 164 00:07:56,725 --> 00:08:00,102 this is where the dinosaurs showed up, 165 00:08:00,102 --> 00:08:03,620 this brown line is where the mammals showed up, 166 00:08:03,620 --> 00:08:07,622 so the dinosaurs showed up along with the mammals 167 00:08:07,622 --> 00:08:09,421 and then of course the dinosaurs died out here. 168 00:08:09,421 --> 00:08:13,965 Our ancestors, when the giant rock hit the earth, 169 00:08:13,965 --> 00:08:15,551 must have been burrowed in holes 170 00:08:15,551 --> 00:08:16,931 and were able to stash some food away, 171 00:08:16,931 --> 00:08:19,662 or who knows what, and didn't get fully affected. 172 00:08:19,662 --> 00:08:22,671 I'm sure most of the large mammals were destroyed, 173 00:08:22,671 --> 00:08:26,105 But what's humbling or almost humorous or 174 00:08:26,105 --> 00:08:28,534 almost ridiculous when you look at this chart, 175 00:08:28,534 --> 00:08:31,854 they put a little dot, you can't see it here, 176 00:08:31,854 --> 00:08:34,561 2 million years ago, the first humans. 177 00:08:34,561 --> 00:08:36,682 And even this is being pretty generous when they say 178 00:08:36,682 --> 00:08:39,435 first humans, these are really the first pre-humans. 179 00:08:39,435 --> 00:08:42,644 The first humans that are the same as us, 180 00:08:42,644 --> 00:08:44,410 if you took one of those babies 181 00:08:44,410 --> 00:08:45,929 and you brought them up in the suburbs and 182 00:08:45,929 --> 00:08:47,198 gave them haircuts and stuff, they would be 183 00:08:47,198 --> 00:08:48,948 the same thing as we are, 184 00:08:48,948 --> 00:08:52,290 those didn't exist until 200,000 years ago. 185 00:08:52,290 --> 00:08:56,249 200,000 to 400,000 years ago, I've seen estimates. 186 00:08:56,249 --> 00:08:58,068 So this actually a very generous 187 00:08:58,068 --> 00:09:01,366 period of time to say first humans, 188 00:09:01,366 --> 00:09:02,876 it's actually 200,000 years ago. 189 00:09:02,876 --> 00:09:07,761 And just to give you an idea of how new we are 190 00:09:07,761 --> 00:09:10,978 and how new our evolution is, it was only 191 00:09:10,978 --> 00:09:12,791 5 million years ago, and I mentioned this 192 00:09:12,791 --> 00:09:13,809 in a previous video, 193 00:09:13,809 --> 00:09:15,216 it was only 5 million years ago. 194 00:09:15,216 --> 00:09:16,299 So this is just to get a sense. 195 00:09:16,299 --> 00:09:17,423 This is 0 years. 196 00:09:17,423 --> 00:09:22,424 Homo sapiens sapiens only around for 200,000 years. 197 00:09:22,424 --> 00:09:24,886 The neanderthals, they were cousin species, 198 00:09:24,886 --> 00:09:26,308 they weren't our ancestors, many people 199 00:09:26,308 --> 00:09:28,262 think they were - they were cousin species, 200 00:09:28,262 --> 00:09:29,793 we come from the same root, 201 00:09:29,793 --> 00:09:32,160 although there are now theories that they might have 202 00:09:32,160 --> 00:09:36,174 remixed in with homo sapiens, so maybe some of us 203 00:09:36,174 --> 00:09:38,773 have some Neanderthal DNA, 204 00:09:38,773 --> 00:09:40,202 and it shouldn't be viewed as an insult, 205 00:09:40,202 --> 00:09:42,236 they had big brains, well, 206 00:09:42,236 --> 00:09:43,243 they didn't actually have big brains, 207 00:09:43,243 --> 00:09:46,346 they had big heads, but that seems to imply big brains 208 00:09:46,346 --> 00:09:49,477 but who knows, we always tend to portray them as 209 00:09:49,477 --> 00:09:51,660 somehow inferior, but I don't want to get into the 210 00:09:51,660 --> 00:09:53,629 political correctness of how to portray 211 00:09:53,629 --> 00:09:57,167 neanderthals, but anyway but this is a very small 212 00:09:57,167 --> 00:10:00,095 period of time. 213 00:10:00,095 --> 00:10:02,183 If you go 2 million years then you get to 214 00:10:02,183 --> 00:10:05,397 the pre-human ancestors and 215 00:10:05,397 --> 00:10:10,594 our family tree, only diverged from the chimpanzees 216 00:10:10,594 --> 00:10:15,003 5 million years ago. If you draw that on this clock 217 00:10:15,003 --> 00:10:17,192 it would barely make... it would be like 2 pixels 218 00:10:17,192 --> 00:10:18,734 or maybe not even 2 pixels, 219 00:10:18,734 --> 00:10:20,940 is when we diverged from the chimpanzees. 220 00:10:20,940 --> 00:10:23,455 So hopefully that gives you a sense of things, 221 00:10:23,455 --> 99:59:59,999 at least for me it really puts things in perspective.