1 00:00:00,219 --> 00:00:06,067 What I want to do in this video is talk about plate tectonics 2 00:00:06,067 --> 00:00:08,404 You have probably heard the words before, 3 00:00:08,404 --> 00:00:14,076 and you might be somewhat familiar with what it discusses. 4 00:00:14,076 --> 00:00:19,150 It's really just the idea that the surface of the earth 5 00:00:19,150 --> 00:00:22,336 is made up of a bunch of these rigid plates, 6 00:00:22,336 --> 00:00:25,474 so it's broken up into a bunch rigid plates, 7 00:00:25,474 --> 00:00:29,010 and this rigid plates move relative to each other 8 00:00:29,010 --> 00:00:32,642 and take everything that's on them for a ride 9 00:00:32,642 --> 00:00:37,003 and the things that are on them include the continents. 10 00:00:37,003 --> 00:00:40,135 so the theory is talking about the movement of these plates. 11 00:00:40,135 --> 00:00:45,404 Over here I have a picture I got off of Wikipedia of the actual plates. 12 00:00:45,404 --> 00:00:47,737 And over here you have the Pacific Plate, 13 00:00:47,737 --> 00:00:51,737 you have the Nazca Plate, the South Amearican Plate, 14 00:00:51,737 --> 00:00:53,803 I can keep going on, we even have the Antarctic Plate, 15 00:00:53,803 --> 00:00:57,886 obviously when you do a projection onto two dimensions of a surface of a sphere 16 00:00:57,886 --> 00:01:02,142 the stuff on the bottom and the top look much bigger than they actually are, Antartica isn't this big 17 00:01:02,142 --> 00:01:06,866 relitive to say North America or South America, we just had to streach it out to fill up the rectangle. 18 00:01:06,866 --> 00:01:09,405 but that's the Antarctic Plate, North American Plate, 19 00:01:09,405 --> 00:01:12,809 and you can see that they're actually moveing relitive to each other, 20 00:01:12,809 --> 00:01:16,000 that's what these arrows are depicting. 21 00:01:16,000 --> 00:01:20,003 You can see right over here the Nazca Plate and the Pacific Plate 22 00:01:20,003 --> 00:01:23,071 are moving away from each other, new land is formed here, 23 00:01:23,071 --> 00:01:25,012 we'll talk more about that in other videos. 24 00:01:25,012 --> 00:01:27,886 You see right over here, in the middle of the Atlantic Ocean, 25 00:01:27,886 --> 00:01:31,743 the African Plate and the South American Plate meet each other 26 00:01:31,743 --> 00:01:33,472 and they're moving away from each other, 27 00:01:33,472 --> 00:01:36,557 which means that more new land, more plate material, 28 00:01:36,557 --> 00:01:40,669 I quess you could say, is somehow being created right here, 29 00:01:40,669 --> 00:01:42,142 we'll be talk about that in future videos, 30 00:01:42,142 --> 00:01:45,808 and pushing these two plates apart. 31 00:01:45,808 --> 00:01:49,944 Now, before we go into the evidence for plate tectonics, 32 00:01:49,944 --> 00:01:53,270 where we'll say some of the more details about how plates are created 33 00:01:53,270 --> 00:01:57,071 and some theories as to why the plates might move, 34 00:01:57,071 --> 00:01:59,404 but I want to get to a little bit of the terminology 35 00:01:59,404 --> 00:02:01,803 of plate tectonics out of the way. 36 00:02:01,803 --> 00:02:04,404 Because sometimes people call them crustal plates, 37 00:02:04,404 --> 00:02:06,898 and that's not exactly right. 38 00:02:06,898 --> 00:02:10,918 I want to show you the difference, two different ways 39 00:02:10,918 --> 00:02:13,409 of classifying the different layers of the Earth 40 00:02:13,409 --> 00:02:15,560 and to think about how they might rely to each other. 41 00:02:15,560 --> 00:02:18,336 So what you traditionally see, and actually I made a video 42 00:02:18,336 --> 00:02:19,896 that goes into a lot more detail of this, 43 00:02:19,896 --> 00:02:24,473 is a breakdown of the chemical layers of the Earth. 44 00:02:24,473 --> 00:02:26,667 When I talk about chemical layers, I'm talking about 45 00:02:26,667 --> 00:02:29,480 what are the constituents of the different layers. 46 00:02:29,480 --> 00:02:31,137 So when you talk within this term, 47 00:02:31,137 --> 00:02:33,738 the tough most layer, which is the thinnest layer, 48 00:02:33,738 --> 00:02:37,675 is the crust. 49 00:02:37,675 --> 00:02:42,739 Then below that is the mantle. 50 00:02:42,739 --> 00:02:47,404 Actually, let me show you the whole Earth where I can draw the scale. 51 00:02:47,404 --> 00:02:50,451 So far we have drawn the crust, 52 00:02:50,451 --> 00:02:54,161 the crust is the outer, the thinnest outer layer of the Earth, 53 00:02:54,161 --> 00:02:57,009 you can imagine the blue line itself is the crust. 54 00:02:57,009 --> 00:02:59,873 Then below that you have the mantel, 55 00:02:59,873 --> 00:03:06,058 so everything between the blue and orange line is the mantle, 56 00:03:06,181 --> 00:03:09,067 let me label the crust. 57 00:03:09,067 --> 00:03:10,532 The crust you can literally view 58 00:03:10,532 --> 00:03:12,733 as the actuall blue pixels over here. 59 00:03:12,733 --> 00:03:16,477 And then inside of the mantle you have the core. 60 00:03:16,477 --> 00:03:18,669 And when you do this very high-level division, 61 00:03:18,669 --> 00:03:21,199 these are chemical divisions. 62 00:03:21,199 --> 00:03:24,539 This is saying that the crust is made up of different types of elements. 63 00:03:24,539 --> 00:03:29,308 Its make-up is different than the stuff that's in the mantle 64 00:03:29,308 --> 00:03:31,336 which is made up of different things 65 00:03:31,336 --> 00:03:34,136 than what's inside of the core. 66 00:03:34,136 --> 00:03:37,812 It's not describing the mechanical properties of it. 67 00:03:37,812 --> 00:03:40,404 When I talk about mechanical properties, I'm talking about ... 68 00:03:40,404 --> 00:03:46,932 so mechanical properties 69 00:03:46,932 --> 00:03:53,142 are whether something is solid and rigid. 70 00:03:53,142 --> 00:03:55,670 Or maybe it's so hot-melted, 71 00:03:55,670 --> 00:03:58,554 it's kind of a magma or plastic solid. 72 00:03:58,554 --> 00:04:04,003 So this would be the most brittle stuff if it gets formed up, 73 00:04:04,003 --> 00:04:08,006 if rock starts to melt a little bit, then you have something like a magma 74 00:04:08,006 --> 00:04:11,405 or you can view it as like a deformable or plastic solid. 75 00:04:11,405 --> 00:04:13,475 When I'm talking about plastic 76 00:04:13,475 --> 00:04:18,308 I'm not talking about the stuff that the case of your cell phone is made up, 77 00:04:18,308 --> 00:04:21,310 I'm talking about it's deformable, this rock is deformable 78 00:04:21,310 --> 00:04:23,895 because it's so hot and it's somewhat melted 79 00:04:23,895 --> 00:04:27,333 it kind of behaves like a fluid. 80 00:04:27,333 --> 00:04:30,070 It actually does behave like a fluid, but it's much more viscous, 81 00:04:30,070 --> 00:04:32,936 it's much thicker and slower-moving than what we would 82 00:04:32,936 --> 00:04:35,078 normally associate with a fluid like water. 83 00:04:35,078 --> 00:04:40,270 So this is a viscous fluid. 84 00:04:40,270 --> 00:04:42,944 And then the most fluid would of course be 85 00:04:42,944 --> 00:04:45,724 the liquid state. 86 00:04:45,724 --> 00:04:48,000 This is what we mean when we talk about mechanical properties. 87 00:04:48,000 --> 00:04:50,721 When you look at this division over here, 88 00:04:50,721 --> 00:04:54,200 the crust is solid, 89 00:04:54,216 --> 00:04:58,403 the mantle actually has some parts of it that are solid, 90 00:04:58,403 --> 00:05:01,210 so the uppermost part of the mantle is solid, 91 00:05:01,210 --> 00:05:06,601 then below that, the rest of the mantle is in this magma, 92 00:05:06,601 --> 00:05:11,144 this deformable, somewhat fluid state, 93 00:05:11,144 --> 00:05:13,555 and depending on what depth you go into the mantle 94 00:05:13,555 --> 00:05:15,543 there are different levels of fluidity, 95 00:05:15,543 --> 00:05:19,892 and then the core, the outer layer of the core is liquid 96 00:05:19,892 --> 00:05:21,602 because the temperature is so high, 97 00:05:21,602 --> 00:05:24,474 the inner core is made up of the same things 98 00:05:24,474 --> 00:05:27,199 and the temperature is even higher 99 00:05:27,199 --> 00:05:29,670 but also the pressure is so high, so it's actually solid. 100 00:05:29,670 --> 00:05:32,275 So that's why the mantle, crust and core differentiation 101 00:05:32,275 --> 00:05:34,345 doesn't tell you about mechanical stuff, 102 00:05:34,345 --> 00:05:36,404 whether it's solid, whether it's magma 103 00:05:36,404 --> 00:05:38,607 whether it's really liquid. 104 00:05:38,607 --> 00:05:40,391 It literally tells you what the make-up is. 105 00:05:40,391 --> 00:05:43,556 Now to think about the make-up, and this is important plate tectonics, 106 00:05:43,556 --> 00:05:47,071 so we talk about these plates, we're not talking about just the crust, 107 00:05:47,071 --> 00:05:49,212 we're talking about the outer rigid layer. 108 00:05:49,212 --> 00:05:52,406 Let me just zoom it a little bit, 109 00:05:52,406 --> 00:05:56,895 let's say we're zoomed in right over there. 110 00:05:56,895 --> 00:05:59,872 So now we have the crust zoomed in, 111 00:05:59,872 --> 00:06:01,555 this right over here is the crust. 112 00:06:01,555 --> 00:06:06,812 And then everything below here, we're actually talking about the upper mantle. 113 00:06:06,812 --> 00:06:10,140 We haven't gone too deep in the mantle right here, 114 00:06:10,140 --> 00:06:17,647 so that's what we call the upper mantle. 115 00:06:17,647 --> 00:06:20,404 Right below the crust the mantle is cool enough 116 00:06:20,404 --> 00:06:23,601 that it is also in real solid form. 117 00:06:23,601 --> 00:06:29,807 So this right here is solid mantle. 118 00:06:29,807 --> 00:06:34,343 And when we talk about the plates, we're actually talking about the outer solid layer, 119 00:06:34,343 --> 00:06:40,000 that includes both the crust and the solid part of the mantle. 120 00:06:40,000 --> 00:06:45,863 We call that the lithosphere. 121 00:06:45,863 --> 00:06:47,975 When people talk about plate tectonics, 122 00:06:47,975 --> 00:06:50,070 they shouldn't say crustal plates. 123 00:06:50,070 --> 00:06:56,178 They should call these lithospheric plates. 124 00:06:56,178 --> 00:07:02,647 Below the lithosphere you have the least viscous part of the mantle 125 00:07:02,647 --> 00:07:07,556 because the temperature is high enough for the rock to melt, 126 00:07:07,556 --> 00:07:13,477 but the pressure isn't so big as in the lower part of the mantle 127 00:07:13,477 --> 00:07:17,666 that the fluid can actually kind of move past each other. 128 00:07:17,666 --> 00:07:20,277 Although it's still pretty viscous, it's still a magma. 129 00:07:20,277 --> 00:07:23,742 So this is still kind of in its magma state, 130 00:07:23,742 --> 00:07:26,308 and this fluid part of the mantle 131 00:07:26,308 --> 00:07:28,404 we can't quite call it liquid yet, 132 00:07:28,404 --> 00:07:31,669 but over large periods of time it does have fliud properties. 133 00:07:31,669 --> 00:07:35,540 This that essetnially the lithisphere is kind of riding on top of 134 00:07:35,540 --> 00:07:41,147 we call this the asthenosphere. 135 00:07:41,147 --> 00:07:43,611 So when we talk about the lithosphere and asthenosphere 136 00:07:43,611 --> 00:07:45,611 we're really talking about machanical layers. 137 00:07:45,611 --> 00:07:47,737 The outer layer, the solid layer is the lithosphere, 138 00:07:47,737 --> 00:07:50,473 the more fluid layer right below that is the asthenosphere. 139 00:07:50,473 --> 00:07:52,558 When we talk about the crust, mantle and core 140 00:07:52,558 --> 00:07:55,003 we're talking about chemical properties, 141 00:07:55,003 --> 00:07:59,000 what are the things actually made up of.