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板块构造:地壳与岩石圈的区别

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what I want to do in this video is talk a little bit about plate tectonics plate tectonics and you've probably heard the word before and are probably or you might be somewhat somewhat familiar with what it what it discusses and it's really just the idea that the surface that the surface of the earth is made up of a bunch of these rigid plates so it's broken up into a bunch of rigid plates and these rigid plates move relative to each other they move relative to each other and take everything that's on them for ride and the things that are on them include the continents so the literally is talking about the movement of these plates and over here I have a picture I got off of Wikipedia of the actual plates and over here you have the Pacific plate let me do that in a darker color you have a Pacific plate you have a Nazca plate you have a South American plate I could keep going on you have an Antarctic plate it's actually obviously whenever you do a projection onto two dimensions of a surface of a sphere the stuff at the bottom and the top look much bigger than they actually are Antarctica isn't this big relative to say North America or South America it's just that we've had to stretch it out to fill up with the rectangle but that's the Antarctic plate North American plate and you can see that they're actually moving relative to each other and that's what these arrows that's what these arrows are depicting you see right over here the Nazca plate and the Pacific plate are moving away from each other new land is forming here we'll talk more about that in other videos you see right over here in the middle of the Atlantic Ocean the African plate and the South American plate meet each other and they're moving away from each other which means that more nool and more plate material I guess you could say is being is somehow being created right here we'll talk about that in future videos and pushing and pushing these two plates apart now before we go into the evidence for plate tonics or even some of the more details about how plates are created and and some theories as to why the plates might move what I want to do is get a little bit of the terminology of plate tectonics out of the way because sometimes people call them crustal plates and that's not exactly right and to show you the difference what I want to do is show you two different ways of classifying the different layers of the earth and then think about how they relate to each other so what you traditionally see and actually I've made a video that goes into a lot more detail of this is a chemical is the breakdown of the chemical layers of the earth when I talk about chemical layers I'm talking about what are the dip what are the constituents of the different layers so when you talk of it in this term the topmost layer which is the thinnest layer is the crust is the crust then below that is the mantle below that is the mantle actually let me do it let me show you the whole earth although I'm not going to draw it to scale so if I were to draw the crust the crust is the outer the thinnest outer layer of the earth you can imagine the blue line itself is the crust then below that you have the mantle so everything between the blue and the orange line is this over here is the mantle mantle let me label the crust the crust you can literally view as the actual blue pixels over here and then inside of the mantle you have the core and when you do this very high-level division we talk these are chemical divisions this is saying that the crust is made up of different types of elements its makeup is different than the stuff that's in then the stuff that's in the mantle which is made up of different things then it what's inside of the core it's not describing the mechanical properties of it and when I talk about mechanical properties I'm talking about whether something is so mechanical properties mechanical properties are whether something is a solid solid and rigid or maybe it's kind of a it's so hot and melted it's kind of a magma or a kind of a plastic solid so then you know this would be the the the most brittle stuff if it gets warmed up if rock starts to melt a little bit then you have something like a magma or you can view it as like a deformable or a plastic solid and we talk about plastic I'm not talking about you know the stuff that you're the case of your cell phone is made up I'm talking about its deformable this rock is deformable because it's so hot and it's somewhat melted it has somewhat it kind of behaves like a fluid it actually does behave like a fluid but it's much more viscous it's much thicker and slower moving than what we would normally associate with the fluid like water so this is this is viscous this is a viscous fluid and then the most fluid would of course be the liquid state would be the liquid state this is what we mean when we talk about the mechanical properties and when you look at these when you look at this division over here the crust is solid the crust is solid the mantle actually has some parts of it that are solid so the uppermost part of the mantle is solid then below that it has a kind of the rest of the mantle is kind of in this magma this deformable somewhat fluid state and depending on what depth you go into the mantle there they're kind of different levels of fluidity and then the core the outer level layer of the core the outer core is liquid because the temperature so high the inner core is made up of the same things and the temperature is even higher but since the pressure so high it's actually solid so that's why the mantle crust and core differentiations don't tell you about mechanical salt whether it's whether it's solid whether it's magma or whether it's really a liquid it just really tells you what the makeup is now to think about the makeup and this is important for plate tectonics so when we talk about these plates we're not talking about just the crust we're talking about the outer rigid layer and we talked about that let me just zoom in a little bit let me just zoom it listen let's say we zoomed in right over there so now we have the crust zoomed in this right here is the crust and then everything below here we're actually talking about the upper mantle so we're talking about we haven't gotten too deep in the mantle right here so that's what we call it the upper mantle upper up or the upper mantle now right below the crust the mantle is cool enough that it is also in in real solid form so this right here this right here is solid solid mantle and when we talk about the plates we're actually talking about the outer solid layer so that includes that includes both the crust and the solid part of the mantle and we call that the lithosphere the lithosphere that when we when people talk about plate tectonics they shouldn't say crustal plates they should call these lithospheric plates litho lithospheric and then below the lithosphere you have you have the least viscous part of the mantle because the temperature is high enough the temperature is high enough for the rock to melt but the pressure isn't so big that it's the the pressure isn't so large as what will happen when you go into the lower part of the mantle that the fluid can actually kind of move past each other although still pretty viscous it's still a magma so we can this is still kind of in it's magma state and this this fluid part of the mantle we can't quite call it a liquid yet but it over large periods of time it does have fluid properties this that essentially the lithosphere is kind of writing on top of we call this the asthenosphere yes then no sphere so when we talk about the lithosphere and asthenosphere we're really talking about mechanical layers the outer layer the solid layer is a little sphere the more fluid layer right below that's the asthenosphere when we talk about the crust mantle and core we are talking about chemical properties what are the things actually made up of