Structure of the earth Structure of the Earth - crust, mantle, core
Structure of the earth
- What I want to do in this video is really make some clarification
- that goes a litle bit more in detail about the different layers of the Earth.
- So let me draw a cross-section of the Earth over here.
- I won't be able to do it perfectly to the scale,
- but I will try to do a little bit better job
- and giving you a little bit of the sense of how thick these layers are.
- So let's say that this is the crust appear
- and I'm going to make the continental crust a little bit thicker,
- so let's say that that is continental crust and this is continental crust.
- And that in between, let me put some oceanic crust which is going to be thinner.
- So this right here is ... actually let me do the oceanic crust in blue,
- but this is not water, this is rock.
- I will do that in purple, that is even better. I don't want it to be that thick.
- So the oceanic crust is thinner than the continental crust
- which I'm trying to depict right over here,
- so this right over here is oceanic crust
- and up here is continental crust.
- And the thickness or how deep you can go and still be in crust, it depends on where you are,
- or we know that near hot-spots the oceanic crust can actually thin out a good bit,
- but roughly, when we talk abou the crust, we are talking about something that is
- 30-60 km deep.
- So if you are on a continent, which I am assuming you are,
- and you dig for 20 km, you will still be in the crust,
- 30 km - probably still in the crust.
- If you dig for 70 km or 100 km, you will probably reach the mantle.
- Remember, what we are describing here, we talk abou the crust, the mantle and the core,
- we are talking abou the chemical make-up, let me make this clear, the chemical make-up.
- The crust is fundametally different than the mantle
- based on the molecules that it is made up of. Based on its composition.
- So let's talk about the mantle now.
- So the mantle layer is like this.
- And once again, this is not the scale,
- because the crust, we are talking about 30-60 km,
- the mantle, we are talking about 2900 to 3000 km thick.
- So this right here is the entire mantle.
- And this is 2900 to 3000 km thick.
- So this isn't even one thirtieth ot that.
- So I would have to draw even narrower than the way I have drawn over here.
- And the mantle itself can be subdivided into the upper mantle and the lower mantle.
- So let me draw this division right over here.
- The upper mantle - there is different ways to define the boundary.
- But the upper mantle is roughly about 700 km down.
- So these are huge distances. I mean this it going straight down.
- So this is the upper mantle.
- Let me write on the actual mantle here.
- This is the upper mantle and this over here is the lower mantle.
- And just to be clear on things:
- So the crust is solid.
- Now when you go into the upper mantle, the upper part of the upper mantle
- we will talk abou that a little bit more, is cool enough to be solid.
- So there is a solid portion of the upper mantle.
- So all of this appear is solid because it's cool enough, it hasn't reached the melting point of those rocks.
- And we have leart in previous videos that the combination of solid part of the upper mantle and the crust combined
- the we call that the lithosphere.
- And when we talk about the lithosphere we are now talking about the mechanical make-up.
- We are now talking about what is solid and what is not solid.
- So this is the lithosphere.
- You go a little bit deeper, right below the lithosphere,
- now the temperatures are high enough for ...
- and I used the word 'liquid' but that is not exactly right.
- You kind of think it is a kind of a deformable solid or plastic solid or magma.
- And that is the asthenosphere. So this area right over here,
- the liquid part; actually I shouldn't use the word 'liquid'.
- It is kind of deformable. It deformes over long perionds of time.
- But it is more fluid than what we normally associate with rock.
- Magma would be a good way to think about it.
- That is what we call the asthenosphere.
- It is fluid. Just not as fluid as water, it is more viscous than something like water.
- So this is the asthenosphere.
- Now, the upper mantle is hard enough for the rock to melt and be fluid,
- but the pressure is low enough for to still be able to kind of move past each.. to be somewhat fluid.
- But once you get even deeper, into the lower mantle, you have higher pressure.
- And so it's still fluid but it's less fluid, it's kind of thicker.
- I guess it's the best way to think about it, the lower mantle. It's thicker.
- So this whole area over here, you can kind of think of it's molten rock, it's fluid,
- but the upper part of the molten rock is more fluid, able to move easier because there is less pressure
- and the pressure is just from all of the rock that is above it,
- remember, gravity is pulling down on everything.
- Every molecule here wants to go down because of gravity.
- So it is applying pressure donw, so the deeper you go, the more pressure you get.
- Now, when we get even deeper than that, we get to the core,
- and the core is divided between the outer core and the inner core.
- So the outer core,
- and then, of course, you have the inner core.
- And just so we have a sense for distances,
- the width or the thickness of the outer core is approximately 2300 km.
- So these are huge distances when you think about thickness.
- You can go donw another 2300 km and you are in the...
- or once you go to the mantle, you can go 2300 km to the outer core,
- and then you are in the inner core, and that essentially takes you the rest.
- That is essentially the centre of the Earth. The inner core.
- Maybe I should draw the boundaries a little bit more to scale.
- It should actually look a little bit more ... like this,
- because the outer core is thicker than the inner.
- So the outer core is, as I said, let me rewrite it.
- Outer core is on the order, it is about 2300 km thick.
- And then you have the inner core.
- I should do it in a hot colour.
- So the inner core right over here, it just kind of takes us in the centre of the Earth,
- and that is a little over 1000 km thick.
- So this is the inner core.
- The number I have is about 1200 km thick.
- And the entire core, both the outer core and the inner core, is mainly nickel and iron.
- When you think about when the Earth was forming,
- what happened is when this whole Earth was super-hot, it was in a kind of a fluid state
- the heavier elements were allowed to sink down when everything was fluid,
- the things that were in between, the things that were lighter would go up,
- and then the gases, thing that would naturally be in gaseous state,
- would kind of bubble up through that fluid,
- kind of the way actually carbon bubbles up in a soda,
- they would eventually bubble up the fluid and would actually form the atmosphere.
- So that is why when you look at the composition of the Earth,
- you have the densiest, the heaviest elements in the centre
- and then the lightest elements are forming the atmosphere.
- The outer core and the inner core, they are made up fundamentally of nickel and iron.
- And their make-up is actually very similar.
- These divisions, chemically they have very similar composition.
- What is different about them is at the outer core
- you have temperatures high enough that nickel and iron can melt,
- but the pressures are low enough that they can still be in a fluid state.
- So this our liquid outer core.
- And this has a pretty low viscosity, especially in relativ to the mantle,
- so that is why people kind of consider this in a more traditionally liquid state.
- But as you get deeper and deeper and deeper, the pressure becomes so huge as you get to the inner core,
- remember all of the weight of all of the rock above you,
- of these thousands of miles of rock above you, is all pushing down on the rock below it.
- So the inner core even that the temperature is really really hot,
- the pressure is so big that them molecules cannot flow past each other,
- they cannot be liquid, they are kind of jam-packed.
- So the inner core because of the high pressure, despite the high temperature, is solid.
- So the difference here is actually a mechanical one - between the outer core and the inner core.
- They are made up of the same things, roughly the same chemical make-up,
- there is just lower pressure on the outside so you can actually be in a fluid state.
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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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When naming a variable, it is okay to use most letters, but some are reserved, like 'e', which represents the value 2.7831...
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At 2:33, Sal said "single bonds" but meant "covalent bonds."
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