Plate tectonics: Difference between crust and lithosphere Plate Tectonics Introduction and Difference between crust and lithosphere
Plate tectonics: Difference between crust and lithosphere
- What I want to do in this video is talk about plate tectonics
- You have probably heard the words before,
- and you might be somewhat familiar with what it discusses.
- It's really just the idea that the surface of the earth
- is made up of a bunch of these rigid plates,
- so it's broken up into a bunch rigid plates,
- and this rigid plates move relative to each other
- and take everything that's on them for a ride
- and the things that are on them include the continents.
- so the theory is talking about the movement of these plates.
- Over here I have a picture I got off of Wikipedia of the actual plates.
- And over here you have the Pacific Plate,
- you have the Nazca Plate, the South Amearican Plate,
- I can keep going on, we even have the Antarctic Plate,
- obviously when you do a projection onto two dimensions of a surface of a sphere
- the stuff on the bottom and the top look much bigger than they actually are, Antartica isn't this big
- relitive to say North America or South America, we just had to streach it out to fill up the rectangle.
- but that's the Antarctic Plate, North American Plate,
- and you can see that they're actually moving relative to each other,
- that's what these arrows are depicting.
- You can see right over here the Nazca Plate and the Pacific Plate
- are moving away from each other, new land is formed 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 new land, more plate material,
- I quess you could say, is somehow being created right here,
- we'll be talk about that in future videos,
- and pushing these two plates apart.
- Now, before we go into the evidence for plate tectonics,
- where we'll say some of the more details about how plates are created
- and some theories as to why the plates might move,
- but I want to get to 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.
- I want to show you the difference, two different ways
- of classifying the different layers of the Earth
- and to think about how they might rely to each other.
- So what you traditionally see, and actually I made a video
- that goes into a lot more detail of this,
- is a breakdown of the chemical layers of the Earth.
- When I talk about chemical layers, I'm talking about
- what are the constituents of the different layers.
- So when you talk within this term,
- the tough most layer, which is the thinnest layer,
- is the crust.
- Then below that is the mantle.
- Actually, let me show you the whole Earth where I can draw the scale.
- So far we have drawn 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 mantel,
- so everything between the blue and orange line is the mantle,
- let me label the crust.
- The crust you can literally view
- as the actuall blue pixels over here.
- And then inside of the mantle you have the core.
- And when you do this very high-level division,
- these are chemical divisions.
- This is saying that the crust is made up of different types of elements.
- Its make-up is different than the stuff that's in the mantle
- which is made up of different things
- than what's inside of the core.
- It's not describing the mechanical properties of it.
- When I talk about mechanical properties, I'm talking about ...
- so mechanical properties
- are whether something is solid and rigid.
- Or maybe it's so hot-melted,
- it's kind of a magma or plastic solid.
- So this would be the most brittle stuff if it gets formed 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 plastic solid.
- When I'm talking about plastic
- I'm not talking about the stuff that the case of your cell phone is made up,
- I'm talking about it's deformable, this rock is deformable
- because it's so hot and it's somewhat melted
- 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 a fluid like water.
- So this is a viscous fluid.
- And then the most fluid would of course be
- the liquid state.
- This is what we mean when we talk about mechanical properties.
- When you look at this division over here,
- 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, the rest of the mantle is in this magma,
- this deformable, somewhat fluid state,
- and depending on what depth you go into the mantle
- there are different levels of fluidity,
- and then the core, the outer layer of the core is liquid
- because the temperature is so high,
- the inner core is made up of the same things
- and the temperature is even higher
- but also the pressure is so high, so it's actually solid.
- So that's why the mantle, crust and core differentiation
- doesn't tell you about mechanical stuff,
- whether it's solid, whether it's magma
- whether it's really liquid.
- It literally tells you what the make-up is.
- Now to think about the make-up, and this is important plate tectonics,
- so we talk about these plates, we're not talking about just the crust,
- we're talking about the outer rigid layer.
- Let me just zoom it a little bit,
- let's say we're zoomed in right over there.
- So now we have the crust zoomed in,
- this right over here is the crust.
- And then everything below here, we're actually talking about the upper mantle.
- We haven't gone too deep in the mantle right here,
- so that's what we call the upper mantle.
- Right below the crust the mantle is cool enough
- that it is also in real solid form.
- So this right here is solid mantle.
- And when we talk about the plates, we're actually talking about the outer solid layer,
- that includes both the crust and the solid part of the mantle.
- We call that the lithosphere.
- When people talk about plate tectonics,
- they shouldn't say crustal plates.
- They should call these lithospheric plates.
- Below the lithosphere you have the least viscous part of the mantle
- because the temperature is high enough for the rock to melt,
- but the pressure isn't so big as in the lower part of the mantle
- that the fluid can actually kind of move past each other.
- Although it's still pretty viscous, it's still a magma.
- So this is still kind of in its magma state,
- and this fluid part of the mantle
- we can't quite call it liquid yet,
- but over large periods of time it does have fliud properties.
- This that essetnially the lithisphere is kind of riding on top of
- we call this the asthenosphere.
- So when we talk about the lithosphere and asthenosphere
- we're really talking about machanical layers.
- The outer layer, the solid layer is the lithosphere,
- the more fluid layer right below that is the asthenosphere.
- When we talk about the crust, mantle and core
- we're talking about chemical properties,
- what are the things actually made up of.
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At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?
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