1 00:00:00,815 --> 00:00:02,471 What I want to do in this video is to try to get a 2 00:00:02,471 --> 00:00:06,063 better understanding of the structure of the earth, 3 00:00:06,063 --> 00:00:08,022 and we're actually going to think about it in two 4 00:00:08,022 --> 00:00:10,351 different ways, so let me just draw half of the earth 5 00:00:10,351 --> 00:00:13,942 over here. That's my best shot at drawing 6 00:00:13,942 --> 00:00:16,680 a half of a circle. We're going to think about it in 7 00:00:16,680 --> 00:00:18,786 two different ways. On the left side, we're going to 8 00:00:18,786 --> 00:00:21,115 think about it as the compositional layers or 9 00:00:21,115 --> 00:00:22,382 the chemical layers. 10 00:00:22,382 --> 00:00:23,871 So, over here, we're going to think about the 11 00:00:23,871 --> 00:00:31,938 chemical structure or the composition of the layer. 12 00:00:31,938 --> 00:00:33,956 And, on the right hand side, we're going to think 13 00:00:33,956 --> 00:00:36,394 about the mechanical properties of the layer. And 14 00:00:36,394 --> 00:00:38,001 when I say the mechanical properties, 15 00:00:38,001 --> 00:00:41,835 I'm really just saying is that layer a solid, rigid 16 00:00:41,835 --> 00:00:45,031 layer, is it kind of a liquid layer, or is it something 17 00:00:45,031 --> 00:00:50,024 in between, a kind of putty-like, non-rigid, solid layer. 18 00:00:50,024 --> 00:00:52,015 So, let's think about it on the chemical or 19 00:00:52,015 --> 00:00:54,548 compositional side first, because to some degree 20 00:00:54,594 --> 00:00:56,232 this is simpler. 21 00:00:56,232 --> 00:00:58,740 The outermost layer is the crust. 22 00:00:58,740 --> 00:01:01,766 That's the layer we're sitting on right here, right now, 23 00:01:01,766 --> 00:01:04,102 I'm assuming - assuming you're on the planet. 24 00:01:04,102 --> 00:01:08,973 It is the outermost and it is obviously solid - we'll 25 00:01:08,973 --> 00:01:11,019 think about that when we talk about the mechanical 26 00:01:11,019 --> 00:01:12,579 side of things. 27 00:01:12,702 --> 00:01:14,471 And it's also the thinnest layer. 28 00:01:14,771 --> 00:01:17,532 Now, crust is not uniform - there's both oceanic crust 29 00:01:17,578 --> 00:01:19,544 and continental crust. 30 00:01:19,544 --> 00:01:21,734 Let me draw the crust on this side as well. 31 00:01:27,965 --> 00:01:30,976 And there's both oceanic crust and continental crust. 32 00:01:30,976 --> 00:01:33,059 So, oceanic crust is thinner crust. 33 00:01:33,059 --> 00:01:35,155 So, let's say that this part right here - let's draw 34 00:01:35,155 --> 00:01:39,621 some thicker crust - we'll call the thicker part 35 00:01:39,621 --> 00:01:43,546 continental crust, which is thicker and less dense 36 00:01:43,546 --> 00:01:46,224 than oceanic crust. So, what I'm doing in this light 37 00:01:46,224 --> 00:01:53,732 green color, this is continental. 38 00:01:54,167 --> 00:01:59,370 And then in this more fluorescent green is oceanic 39 00:01:59,370 --> 00:02:00,059 crust. 40 00:02:00,089 --> 00:02:02,436 And the oceanic crust is pretty thin, in the order of 41 00:02:02,436 --> 00:02:09,820 five to ten kilometers thick. 42 00:02:09,820 --> 00:02:11,258 Now, when I talk about oceanic crust I'm not talking 43 00:02:11,258 --> 00:02:13,784 about the oceans, the liquid part, the water, I'm 44 00:02:13,784 --> 00:02:15,705 talking about the rock that kind of holds the 45 00:02:15,705 --> 00:02:16,205 water 46 00:02:16,205 --> 00:02:18,105 The rock underneath the ocean. 47 00:02:18,105 --> 00:02:20,205 So, this is five to ten kilometers thick. 48 00:02:20,205 --> 00:02:23,269 If you were to go to the bottom of the ocean, sit on 49 00:02:23,269 --> 00:02:26,440 the rock, then drill, you would have to drill five to ten 50 00:02:26,440 --> 00:02:28,811 kilometers to get through that layer, this 51 00:02:28,811 --> 00:02:30,652 compositional layer. 52 00:02:30,922 --> 00:02:32,330 So, this is five to ten kilometers. 53 00:02:32,361 --> 00:02:34,669 And the continental crust is about ten to seventy 54 00:02:34,669 --> 00:02:36,007 kilometers thick. 55 00:02:40,717 --> 00:02:43,136 And obviously they are both rigid, they are both 56 00:02:43,136 --> 00:02:45,041 solid rock. 57 00:02:45,257 --> 00:02:48,376 Now below, when you think of composition, what the 58 00:02:48,376 --> 00:02:50,055 layers are made up of. 59 00:02:50,055 --> 00:02:51,940 The next layer below that, this is actually the biggest 60 00:02:51,940 --> 00:02:55,411 layer of the earth by volume, is the mantle. 61 00:02:58,280 --> 00:03:00,568 So, let me draw it like that. 62 00:03:00,568 --> 00:03:02,468 I always have trouble drawing the right hand side 63 00:03:02,468 --> 00:03:03,929 of the circle. 64 00:03:06,412 --> 00:03:08,258 So this is the mantle right over here. 65 00:03:13,907 --> 00:03:16,092 And once again we differentiate it from the crust 66 00:03:16,092 --> 00:03:19,041 because it's composed of different types of rock 67 00:03:20,009 --> 00:03:21,198 Now, we go even deeper. 68 00:03:21,198 --> 00:03:23,637 Let me give you the depths here. So, the mantle starts 69 00:03:23,637 --> 00:03:26,113 below the crust, right below the continental and 70 00:03:26,113 --> 00:03:33,740 oceanic crust, and it goes about 2,900 kilometers 71 00:03:33,740 --> 00:03:34,424 deeper. 72 00:03:34,424 --> 00:03:37,320 So it is much, much, much thicker than the crust. 73 00:03:37,320 --> 00:03:42,516 The crust is on the order of maybe 5 to 70 km thick. 74 00:03:42,516 --> 00:03:46,418 This is much, much thicker. So, even though I drew 75 00:03:46,418 --> 00:03:50,025 the crust thin, I didn't draw it thin enough relative to 76 00:03:50,025 --> 00:03:52,483 how thick I've draw the mantle. 77 00:03:52,483 --> 00:03:54,086 This isn't drawn to scale. 78 00:03:54,086 --> 00:03:56,863 Now you go even deeper than that, you get kind of 79 00:03:56,863 --> 00:04:01,217 the densest part of the earth, and that is the core. 80 00:04:02,553 --> 00:04:04,355 There's going to be a couple of themes here, 81 00:04:04,355 --> 00:04:05,747 especially when we think of the mechanical 82 00:04:05,747 --> 00:04:09,775 properties of the earth, is that the deeper you get, 83 00:04:09,775 --> 00:04:11,469 you're going to get denser elements and you're going 84 00:04:11,469 --> 00:04:14,610 to have more heat and more pressure. 85 00:04:14,610 --> 00:04:16,436 The reason why you're going to have denser elements 86 00:04:16,436 --> 00:04:17,721 Is when the Earth was first 87 00:04:17,721 --> 00:04:19,359 forming and it was kind of in its molten state, 88 00:04:19,359 --> 00:04:22,021 the denser elements sunk to the bottom, and the 89 00:04:22,021 --> 00:04:25,335 lighter elements would kindc of rise to the top. 90 00:04:25,335 --> 00:04:26,281 They would kind of rise to the top. They would have 91 00:04:26,281 --> 00:04:28,412 this bouyancy because they are less dense than 92 00:04:28,412 --> 00:04:31,801 everything around it. Even the gases would bubble 93 00:04:31,801 --> 00:04:35,345 up and form our atmosphere. 94 00:04:35,545 --> 00:04:36,782 So, that's why in general, the densest things are 95 00:04:36,782 --> 00:04:39,563 at the center and the least dense things are on 96 00:04:39,563 --> 00:04:42,144 the outside - they're in our atmosphere. 97 00:04:42,144 --> 00:04:43,690 And the core, once again, it's composition is 98 00:04:43,690 --> 00:04:46,418 fundamentally different than the mantle and crust. 99 00:04:46,418 --> 00:04:50,133 We believe that it is mainly metals, in particular 100 00:04:50,133 --> 00:04:51,622 iron and nickel. 101 00:04:51,622 --> 00:04:53,967 So that's the structure of the layers of the earth from 102 00:04:53,967 --> 00:04:55,991 a composition point of view, a chemical point of 103 00:04:55,991 --> 00:04:56,832 view. 104 00:04:56,832 --> 00:04:58,912 Now, let's kind of think of the same layers, but we're 105 00:04:58,912 --> 00:05:01,472 going to think more in terms of what's liquid, what's 106 00:05:01,472 --> 00:05:04,299 rigid and solid, and what's in between. 107 00:05:04,299 --> 00:05:09,886 So the outermost rigid layer of the earth is made up 108 00:05:09,886 --> 00:05:13,462 of the crust, both the continental and oceanic crust, 109 00:05:13,462 --> 00:05:18,671 and the coolest top layer of the mantle. Let me draw 110 00:05:18,671 --> 00:05:24,661 that in pink. 111 00:05:24,661 --> 00:05:27,673 So what I'm drawing in pink is the cool, rigid, solid 112 00:05:27,673 --> 00:05:32,534 part of the mantle. 113 00:05:32,534 --> 00:05:35,877 So it is solid rock, part of the mantle is solid rock, 114 00:05:35,877 --> 00:05:39,661 it's composition is different from the crust, but they are both 115 00:05:39,661 --> 00:05:44,863 rigid. So if you combine this top most layer of the 116 00:05:44,863 --> 00:05:49,205 mantle with the crust, then you're talking about the 117 00:05:49,205 --> 00:05:51,538 lithosphere. 118 00:05:51,538 --> 00:05:55,847 So this is the lithosphere. 119 00:05:55,847 --> 00:05:59,407 And this essentially gets you about, depening on 120 00:05:59,407 --> 00:06:04,950 where you are on the surface of the earth, is 10-200 121 00:06:04,950 --> 00:06:11,164 kilometers thick. And most of the time, it's closer to 122 00:06:11,164 --> 00:06:15,258 the high end of the range. The 10 is kind of where you 123 00:06:15,258 --> 00:06:17,556 have hot spots in the mantle and it's essentially been 124 00:06:17,556 --> 00:06:22,379 able to dissolve part of the lithosphere, we'll talk 125 00:06:22,379 --> 00:06:25,126 about that more when we talk about plate tectonics. 126 00:06:25,126 --> 00:06:29,375 These are actually lithospheric plates, and the 127 00:06:29,375 --> 00:06:31,744 lithosphere is actually moving on top of the lower 128 00:06:31,744 --> 00:06:35,204 layers of the mantle. 129 00:06:35,204 --> 00:06:38,478 The lithosphere it is rigid, solid, it's made up of 130 00:06:38,478 --> 00:06:42,961 the crust and the uppermost layer of the mantle. 131 00:06:42,961 --> 00:06:46,946 Now, you go a little bit deeper, the temperatures 132 00:06:46,946 --> 00:06:48,533 and pressures increased, but now the 133 00:06:48,533 --> 00:06:50,344 temperatures have increased enough - you have the 134 00:06:50,344 --> 00:06:52,873 same composition as the uppermost, the rigid part of 135 00:06:52,873 --> 00:06:55,429 the mantle, but the temperatures have now gone up 136 00:06:55,429 --> 00:06:58,533 enough that it now turns it now into not quite a 137 00:06:58,533 --> 00:07:03,416 liquid, we won't call it a liquid, it still transmits 138 00:07:03,416 --> 00:07:05,197 a certain type of waves that liquids wouldn't transmit. 139 00:07:05,197 --> 00:07:08,803 it's more of like a putty-like texture, it has fluid-like 140 00:07:08,803 --> 00:07:12,682 properties, it can float, it's way more viscous than what 141 00:07:12,682 --> 00:07:16,140 we'd associate with most liquids, so it's not rigid and 142 00:07:16,140 --> 00:07:19,245 solid, it can have convection going on in it, but it's 143 00:07:19,245 --> 00:07:22,333 not a liquid - it still will transmit some types of waves 144 00:07:22,333 --> 00:07:24,156 that liquids won't. 145 00:07:24,156 --> 00:07:26,374 This is called the asthenosphere, this kind of jelly, 146 00:07:26,374 --> 00:07:30,932 putty layer. It's like that, because it's so hot that the 147 00:07:30,932 --> 00:07:33,540 rock has somewhat melted. 148 00:07:33,540 --> 00:07:40,918 So, this is, this layer right here, is the asthenosphere. 149 00:07:40,918 --> 00:07:43,377 I've seen some spellings that have an 'e' after the a, 150 00:07:43,377 --> 00:07:46,071 I think that's the european spelling. 151 00:07:46,071 --> 00:07:48,649 The aesthenosphere obviously starts right below the 152 00:07:48,649 --> 00:07:49,980 lithosphere. 153 00:07:49,980 --> 00:07:52,196 It's what the lithospheric plates, when we are talking 154 00:07:52,196 --> 00:07:53,920 about tectonic plates, are riding on top of. 155 00:07:53,920 --> 00:07:57,658 It's kind of the gummy layer that allows the rigid 156 00:07:57,658 --> 00:08:00,278 layer to kind of move, actually move on top. 157 00:08:00,278 --> 00:08:03,648 So it starts below the lithosphere and it ends at 158 00:08:03,648 --> 00:08:08,200 around 660 kilometers deep. So, this right here is 159 00:08:08,200 --> 00:08:12,628 660 kilometers deep. 160 00:08:12,628 --> 00:08:14,764 And then you go even deeper than that, and now the 161 00:08:14,764 --> 00:08:20,763 pressures are so big that even are even higher, the 162 00:08:20,763 --> 00:08:25,082 pressures are so big that the same material can't 163 00:08:25,082 --> 00:08:26,840 have fluid motion anymore. 164 00:08:26,840 --> 00:08:28,632 It's essentially been jammed together. 165 00:08:28,632 --> 00:08:31,907 So you can imagine if you have things that are 166 00:08:31,907 --> 00:08:36,364 somewhat fluid, that means they can kind of slide 167 00:08:36,364 --> 00:08:38,958 past each other, maybe very slowly. 168 00:08:38,958 --> 00:08:43,239 But, if you increase the pressure enough, they'll be 169 00:08:43,239 --> 00:08:45,390 jammed into each other, and that's essentially what 170 00:08:45,390 --> 00:08:47,372 happens in the next layer of the mantle. 171 00:08:47,372 --> 00:08:48,959 All of these layers of the mantle are made up of the 172 00:08:48,959 --> 00:08:52,124 same thing, it's just a difference of pressure. 173 00:08:52,124 --> 00:08:54,353 So, the next layer of the mantle is called the 174 00:08:54,353 --> 00:08:57,969 mesosphere. 175 00:08:59,307 --> 00:09:02,342 Mesosphere. 176 00:09:02,342 --> 00:09:04,284 This is called the mesosphere, but there is also a 177 00:09:04,284 --> 00:09:07,349 layer of our atmosphere right above the stratosphere 178 00:09:07,349 --> 00:09:09,082 that's called the mesosphere. 179 00:09:09,082 --> 00:09:10,894 And so, don't get confused here, these are two 180 00:09:10,894 --> 00:09:12,403 different mesosphere-s. 181 00:09:12,403 --> 00:09:15,120 And this layer, the pressure is so big, that now we 182 00:09:15,120 --> 00:09:19,129 are rigid again. We are kind of definetely solid now. 183 00:09:19,129 --> 00:09:21,429 None of this debate about a little bit of fluid motion 184 00:09:21,429 --> 00:09:23,178 because the pressure is so big. 185 00:09:23,178 --> 00:09:28,466 Now you go a little bit deeper, you are in the core, 186 00:09:28,466 --> 00:09:32,868 the metallic core, the temperatures are so high, that 187 00:09:32,868 --> 00:09:34,997 even though the pressures are high because we 188 00:09:35,027 --> 00:09:37,442 have a compositional change, we are at pressures 189 00:09:37,442 --> 00:09:40,894 where this type of mesospheric rock is rigid, but 190 00:09:40,894 --> 00:09:45,613 metals at this temperature can be fluid, can actually 191 00:09:45,613 --> 00:09:46,600 be liquid. 192 00:09:46,600 --> 00:09:56,638 We actually have a liquid outer core. 193 00:09:56,638 --> 00:09:58,751 The entire core, as far as we know, is made up of 194 00:09:58,751 --> 00:10:01,381 the same stuff, just the outer part of the core, the 195 00:10:01,381 --> 00:10:04,926 temperatures are high enough to melt the metals, 196 00:10:04,926 --> 00:10:07,210 but the pressures aren't so high enough to make 197 00:10:07,210 --> 00:10:08,457 them solid. 198 00:10:08,457 --> 00:10:10,298 They're definitely high enough to kind of make more 199 00:10:10,298 --> 00:10:11,474 rocky materials solid, but not the metals. 200 00:10:11,474 --> 00:10:15,143 And then you go even deeper, now the temperature 201 00:10:15,143 --> 00:10:17,720 keep going up, the pressure is so strong that even 202 00:10:17,720 --> 00:10:19,424 the metals are solid. 203 00:10:19,424 --> 00:10:24,517 So, this is the solid, the solid, inner core. 204 00:10:24,517 --> 00:10:26,149 So, when you think about the mechanical 205 00:10:26,149 --> 00:10:28,233 properties, the innermost, and just so you know the 206 00:10:28,233 --> 00:10:30,724 total distances we're talking about, the outer core 207 00:10:30,724 --> 00:10:33,922 starts at, actually, I didn't tell you where the 208 00:10:33,922 --> 00:10:39,966 mesosphere - the mantle ends at about 2900 209 00:10:39,966 --> 00:10:41,801 kilometers deep, so that's clearly where the 210 00:10:41,801 --> 00:10:44,332 mesosphere ends as well, because the mesosphere 211 00:10:44,347 --> 00:10:47,057 is kind of the lower mantle. 212 00:10:47,057 --> 00:10:50,199 This is 2900 kilometers deep. 213 00:10:50,199 --> 00:10:51,995 Then you go even deeper. 214 00:10:51,995 --> 00:10:53,782 Now, you're in the liquid outer core, and that extends 215 00:10:53,782 --> 00:10:57,977 from about 2900 kilometers deep to about 5100 216 00:10:57,977 --> 00:10:59,804 kilometers deep. 217 00:10:59,804 --> 00:11:02,389 So I really should, I frankly should make the 218 00:11:02,389 --> 00:11:05,043 liquid core in my drawing a little wider. 219 00:11:05,043 --> 00:11:11,608 So, this depth is about 5100 kilometers deep. 220 00:11:11,608 --> 00:11:13,806 And then obviously, you have the center of the earth, 221 00:11:13,806 --> 00:11:17,546 and the entire radius of the earth is about 6400 222 00:11:17,546 --> 00:11:19,157 kilometers. 223 00:11:19,157 --> 00:11:21,461 So, hopefully that clarifies things when you hear 224 00:11:21,461 --> 00:11:24,216 people talking about the lithosphere or the mantle, 225 00:11:24,216 --> 00:11:26,258 they're really talking about mechanical versus 226 00:11:26,258 --> 00:11:27,327 composition. 227 00:11:27,327 --> 00:11:29,370 And when we talk about mechanical, solid inner core, 228 00:11:29,370 --> 00:11:33,557 liquid outer core, essentially solid mesosphere, 229 00:11:33,557 --> 00:11:37,103 and then you have something, kind of a spongy, 230 00:11:37,103 --> 00:11:40,501 somewhat fluid, not-solid, not-liquid aesthenosphere 231 00:11:40,501 --> 00:11:42,629 that the lithosphere can ride on top of, 232 00:11:42,629 --> 00:11:44,517 and then you have your actual rigid, solid lithosphere 233 00:11:44,517 --> 00:11:48,481 made up of the uppermost part of the mantle and the 234 00:11:48,481 --> 00:11:49,773 crust.