Title: Structure of the Earth
Publish Date: Feb 2011
Description: Is it a coincidence that Africa and South America could fit like puzzle pieces? Why do earthquakes happen where they do? What about volcanoes and mountains? Are all of these ideas linked? Yes, they are. This tutorial on plate-tectonics explains how and why the continents have shifted over time. In the process, we also explore the structure of the Earth, all the way down to the core.
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Time Transcript Action
00:00:00 What i want to do in this video is really make some clarifications and go a little
00:00:03 bit more in detail about the different layers of the earth
00:00:08 so let me draw
00:00:10 let me draw a cross section of the earth over here and i'll try to do it
00:00:13 and i wouldnt' be able it perfectly to scale but i'll try to do a little bit better job
00:00:17 and give me a little bit of a sense
00:00:20 of how thick these layers are so let's say that this is the crust appear
00:00:24 and i want to make the continental crust a little bit thicker
00:00:28 so let say that is continental crust and this is continental crust
00:00:32 and that in between let me put some oceanic crust which is going to be thinner
00:00:36 so this right here is, let me try it in a different color
00:00:40 let me do the oceanic crust in blue but this is not a water and this is rock
00:00:44 a blue and purple it even better
00:00:46 i want to be that thick so we draw the oceanic crust
00:00:50 that is thinner than the continental crust which i'm trying to depict right over here
00:00:54 so this right over here is oceanic
00:00:58 oceanic
00:01:00 crust
00:01:01 and up here is continental crust
00:01:06 continental
00:01:09 continental crust
00:01:10 and the thickness or how deep you can go and still be in crust
00:01:14 it depends on
00:01:15 where you are and we know that near hot spots the oceanic crust can actually
00:01:20 thin out a good bit
00:01:21 but roughly when we talk about the crust were talking about something that's
00:01:25 thirty to sixty kilometers deep
00:01:28 so thirty to sixty
00:01:30 kilometres 's deep so
00:01:32 if you are on our continent which i'm assuming you are and you dig for twenty
00:01:36 kilometres you will still be in the crust thirty kilometres probably still in the
00:01:39 crust if you dig for seventy kilometers or a hundred kilometers
00:01:43 you will probably reach of the mantle
00:01:47 and remember what we're describing here we talk about the crust, the mantle and the core
00:01:51 we're talking about the chemical makeup let me make this clear we're talking
00:01:54 about the chemical makeup
00:01:56 the chemical makeup the crust is
00:01:59 fundamentally different then the mantle based on
00:02:02 the molecules that it is made up of me based on its composition so let's talk
00:02:06 about the mantle now
00:02:08 so the mantle
00:02:10 layer like this once again this is not to scale because
00:02:13 the crust we're talking about thirty to sixty kilometers the mantle we're
00:02:17 talking about on the order about twenty nine hundred or three thousand
00:02:20 kilometers thick
00:02:21 so this right here is the entire mantle
00:02:25 so that's the mantle and this is
00:02:28 twenty nine hundred
00:02:30 to three thousand
00:02:32 three thousand kilometers tick
00:02:35 so this isn't even one thirtieth
00:02:37 of that so to draw even narrower than the way of drawn over here and the
00:02:41 mantle itself can be subdivided into the upper mantle and the lower mantle
00:02:46 so let me draw this division
00:02:48 this division right over here the upper mantle and there's different ways to
00:02:52 define the boundary but you could
00:02:54 the upper mantle is roughly about seven hundred kilometres down
00:02:58 so this is huge distances and this is going straight down
00:03:02 so this is the upper mantle
00:03:04 let me write it on the actual mantle here
00:03:07 this is the upper mantle and this over here is the lower
00:03:13 the lower mantle and just to be clear on things so the crust is solid
00:03:18 now when you go into the upper mantle
00:03:21 the upper part of the up upper mantle we will talk about that a little bit more
00:03:25 because it is cool enough to be solid
00:03:27 so there is a solid portion
00:03:29 there is a solid portion of the upper mantle so all of this up here
00:03:34 is solid because cool enough that hasn't reached the melting point of those
00:03:39 of those rocks and we learned in previous videos that the combination of the solid part
00:03:45 the solid part of the upper mantle
00:03:48 and of the crust combined we call that the lithosphere we talk about the
00:03:51 lithosphere we're not talking about the mechanical makeup we're not talking about what solid
00:03:55 and what's not solid so this is the lithosphere
00:03:59 this is the lithosphere you go a little bit deeper right below the lithosphere
00:04:04 now the temperatures are high enough for
00:04:07 and i use the word liquid but that's not exactly right you can kind of think
00:04:10 of it is kind of a deformable solid or plastic solid or magma and that's the
00:04:16 Asthenosphere
00:04:17 so this area right over here
00:04:20 this layer area
00:04:22 right over here the liquid part
00:04:24 actually i should use the word liquid kind of the deformable deformed over long
00:04:27 periods of time
00:04:30 it is it is more fluid that we normally associate with rock magma would be a
00:04:34 good way to think about it that's what we call the Asthenosphere
00:04:38 it is fluid
00:04:39 just not as fluid as water is more viscous than something like water so
00:04:43 this is the Asthenosphere
00:04:45 Asthenosphere
00:04:47 now the upper mantle is able
00:04:49 it's hot enough for the the rock to melt and be fluid
00:04:53 and the for the pressure is low enough for to not
00:04:56 for just still to be able to kind of move past as itself to still
00:05:00 to have to be some what fluid, but that one even you get deeper
00:05:07 into the lower mantle into the lower mantle you even hot you have higher pressure
00:05:11 higher pressure
00:05:13 and so it has actually
00:05:14 it's still fluid but it's less fluid is less
00:05:17 it's it's it's kind of
00:05:19 thicker i guess is the best way to think about it in the lower mantle
00:05:22 it's thicker
00:05:23 so this whole area over here you could kind of think of it is melted rocks
00:05:28 it's fluid
00:05:29 but the upper part of the melted rock can it's more fluid able to move
00:05:33 easier because there is less pressure and the pressures are from all
00:05:36 of the rock that's above it remember gravity is
00:05:39 pulling down on everything
00:05:41 gravity every every molecule here wants to go down because of the gravity
00:05:44 it's it's applying pressure downward so the deeper you go
00:05:48 the more pressure you get
00:05:50 when we get even deeper than that we get to the core and the core is divided between
00:05:54 the outer core and the inner core
00:05:57 so they are outer core
00:06:00 outer core
00:06:02 outer core and then of course you have the inner core
00:06:07 the inner
00:06:09 inner core and so we have a sense for the distances the width or the thickness of the outer core
00:06:15 is approximately twenty three hundred kilometers so there's a huge distances
00:06:19 and you think about thickness you can go down another twenty three hundred
00:06:22 kilometers and you're the
00:06:23 or 's once you go to the mantle you can go to twenty three hundred kilometres to the outer core
00:06:27 and then you in the inner core and that it's essentially takes to the rest that's essentially
00:06:30 the center of the earth in the inner core
00:06:32 maybe i should draw it
00:06:34 maybe i should draw the boundaries a little bit more the scale we do it this way
00:06:38 should actually look a little bit more like
00:06:40 a little bit
00:06:42 a little bit more like this because the outer core is thicker than the inner core
00:06:47 the outer core is as i said
00:06:50 we write rewrite it
00:06:51 outer core is on the order it's about twenty three hundred
00:06:56 kilometres thick and then you have your inner core
00:06:59 you have your i shouln't do it, i should do it in the hot color
00:07:03 so the inner core right over here is is kinda takes us to the center of the
00:07:07 earth and that's a little over color that's or a little over a thousand
00:07:10 kilometers thick so this is the inner core
00:07:13 inner core the number i have is about twelve hundred
00:07:17 twelve hundred kilometres thick and both of the the entire core and both the
00:07:21 outer core and the inner core
00:07:23 is mainly nickel and iron and think about when the earth was forming what happens is the
00:07:26 whole earth was super hot and that was is kind of in a fluid state
00:07:29 the heavier elements were allowed to
00:07:32 the heavier elements were allowed to sink down when everything was fluid and the
00:07:35 things that are in between would kind of
00:07:37 when things are rely would go up
00:07:39 and in the gases things that would naturally be in the gaseous state
00:07:41 we kind of bubble up
00:07:43 would kind of bubble up through that fluid you know kind of the way the way
00:07:47 actually you know carbon bubbles up and uh... in a in a soda
00:07:51 it is eventually bubble up of the fluid and i would actually form the atmosphere so
00:07:54 that's why when you look at the composition of that you have the densest the heaviest
00:07:58 elements in the center
00:07:59 and in the lightest elements are forming
00:08:01 the atmosphere
00:08:02 and the outer core in the inner core
00:08:04 they are made up predominately of nickel and iron
00:08:08 nickel and iron
00:08:11 and their makeup is actually very similar so uh... this division
00:08:15 chemically they are uh... they have a very similar composition
00:08:18 what's different about them is
00:08:19 at the outer core
00:08:21 you have temperatures high enough that nickel and iron can melt
00:08:24 but the pressures are low enough that they can still be in a fluid state
00:08:28 so this is our liquid
00:08:30 this is our a liquid outer core
00:08:33 and this has a pretty low viscosity especially even relative to the mantle so that's why people
00:08:39 kind of could consider this and kind of a more traditional liquid state
00:08:42 but as you get deeper and deeper and deeper the pressure becomes so huge
00:08:47 as you get to the inner core remember all of the weight of every
00:08:50 of all of the rock above you these thousands of miles of rock above you
00:08:54 is all pushing down on the rock below it so the inner core even the
00:08:58 temperatures really really really hot
00:09:00 the pressure is so big
00:09:02 but the molecules can't flow past each other and they can't be liquid
00:09:06 they're kind of jammed packed and so the inner core because of the high-pressure
00:09:10 despite the high temperature is solid
00:09:13 it's solid so the difference here is actually a mechanical one
00:09:17 between the outer core in the inner core there made up of the same things roughly the
00:09:20 same chemical makeup is just slightly lower or lower pressure on the outside
00:09:24 so you can actually be in a fluid state
00:09:27 so hopefully that clarifies and gives you a little bit of depth
00:09:29 on the makeup of the earth