Compositional and mechanical layers of the earth

WEBVTT
Kind: captions
Language: en

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What I want to do
in this video is

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try to get a better
understanding

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of the structure of the earth.

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And we're actually
going to think

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about it in two different ways.

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So let me just draw half
of the earth over here.

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That's my best shot at
drawing half of a circle.

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And what we're going to do is
think about it in two ways.

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And on the left-hand
side we're going

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to think about it as the
compositional layers,

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or the chemical layers.

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So over here we're
going to think

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about the chemical structure,
or the composition of the layer.

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And on the right-hand
side we're going

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to think about the mechanical
properties of the layer.

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And when I say the mechanical
properties I'm really

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just saying is that layer
kind of a solid, rigid layer?

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Is it kind of a liquid layer?

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Or is it something in between, a
kind of a putty-like non-rigid,

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solid layer?

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So let's think about
it on the chemical

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or the compositional side
first, because to some degree

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this is simpler.

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So the outermost
layer is the crust.

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That's the layer that we're
sitting on right here, right

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now, I'm assuming.

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I'm assuming you're
on the planet.

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So this right here is the crust.

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It is the outermost,
it's obviously solid.

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We'll think about
that when we talk

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about the mechanical
side of things.

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And it's also the
thinnest layer.

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And crust is not uniform.

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There's both oceanic crust
and continental crust.

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And let me draw the crust
on this side as well.

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So let me draw some
crust over here.

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We've got some crust
right over there.

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And there is both oceanic
crust and continental crust.

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So oceanic crust
is thinner crust.

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So let's say this
part right here--

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Let me draw some thicker
crust right over here.

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We'll call the thicker
stuff the continental crust,

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which is thicker and less
dense than the oceanic crust.

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So what I'm doing in
this light green color,

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this is continental.

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So this right here
is continental.

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And then in this kind of
more fluorescent green,

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this is oceanic crust.

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And the oceanic
crust is pretty thin.

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It's on the order of
about 5 or 10 kilometers.

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So let's just call this,
this is approximately 5 to 10

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kilometers thick.

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And when I talk
about oceanic crust

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I'm not talking
about the oceans.

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I'm not talking about the
liquid part, the water.

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I'm talking about
the rock that kind of

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holds the water, the rock
underneath the oceans.

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And so this is 5 to
10 kilometers thick.

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If you were to go to
the bottom of the ocean

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and you were to sit on the
rock and then drill you'd

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have to drill about
5 to 10 kilometers

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to get through that layer,
this compositional layer.

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So this is 5 to 10 kilometers.

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And the continental crust
is about 10 to 70 kilometers

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thick.

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And obviously, they
are both rigid.

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They are both solid rock.

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Now below, when you
think about composition,

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or what the layers are made up
of, the next layer below that,

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this is actually the biggest
layer of the earth by volume,

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is the mantle.

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Let me draw it like that.

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I always have trouble
drawing the right-hand side

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of the circle.

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So this is the mantle
right over here.

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This is all the mantle.

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And once again, we
differentiate it from the crust

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because it's composed of
different types of rock.

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Now, you go even deeper, and
let me give you the depths here.

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So the mantle starts
right below the crust,

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right below the oceanic
and the continental crust.

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And it goes about 2,900
kilometers deeper.

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So it's much, much, much
thicker than the crust.

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The crust is on the order of 5
to maybe 70 kilometers thick.

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This is much, much thicker.

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So even though I've drawn
the crust fairly thin

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I didn't draw it thin enough
relative to how thick I've

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drawn the mantle.

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This isn't drawn to scale.

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Now, you go even
deeper than that you

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get the densest
part of the earth.

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And that is the core.

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And there's going to
be couple of themes

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here, especially when we think
about the mechanical properties

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of the earth, is the deeper you
get you're going to get denser

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elements, and you're
going to have more heat

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and more pressure.

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And the reason why you're
going to have denser elements

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is when Earth was
first forming and it

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was kind of in this molten
state, the denser elements

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just kind of sunk to the bottom,
and the lighter elements would

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kind of rise to the top.

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They would have this
buoyancy because they're

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less dense than
everything around it.

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And really even the gases
would kind of bubble up,

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would essentially bubble
up and form our atmosphere.

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So that's why, in general,
the densest things

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are in the center and
the least dense things

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are on the outside.

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They're in our atmosphere.

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And the core, once
again, its composition

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is fundamentally different
than the mantle and the crust.

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We believe that
it's mainly metals,

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and in particular
iron and nickel.

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So that's the
structure of the layers

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of the earth from a
composition point of view,

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from a chemical point of view.

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Now, let's kind of think
about the same layers,

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but we're going to think more
in terms of what's liquid,

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what's rigid and solid,
and what's in between.

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So the outermost rigid
layer of the earth

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is made up of the crust,
both the continental

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and the oceanic crust, and
kind of the coolest top layer

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of the mantle.

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So let me draw that in pink.

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So this layer right over here.

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So what I'm drawing in pink
is the cool, rigid, solid part

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of the mantle.

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So it is solid rock, the part of
the mantle that is solid rock.

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It's composition is
different than say,

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the continental crust,
but they are both rigid.

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So if you combine
this top-most layer

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of the mantle with
the crust then you're

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talking about the lithosphere.

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So this is the lithosphere.

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And this essentially gets
you about, the lithosphere,

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depending on where you are on
the surface of the earth is

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10 to 200 kilometers thick.

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And most of the time it's closer
to the high end of this range.

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The 10 is kind of where you
have hot spots in the mantle

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and it's essentially been
able to kind of dissolve

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parts of the lithosphere.

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Well, we'll talk
more about that when

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we talk about the actual
plate tectonics of it all.

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And when we talk
about plate tectonics

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the plates are actually
lithospheric plates.

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It's actually the
lithosphere that's

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moving on top of the lower
layers of the mantle.

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So the lithosphere, it is rigid.

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It is solid.

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It's made up of the crust
and the uppermost layer

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of the mantle.

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Now, you go a little bit
deeper, the temperatures

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and the pressures increase.

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But now the temperatures
have increased enough,

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you have the same composition
as the uppermost, the rigid part

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of the mantle, but
the temperatures

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have now gone up
enough that it now

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turns into not quite a liquid.

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We won't call it a liquid.

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It actually still
transmits the type of waves

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that liquids would not transmit.

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It's more of like a
putty type texture.

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It has fluid properties.

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It can flow.

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It's way more
viscous than what we

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would associate
with most fluids.

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So it's not rigid and solid.

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It can have convection going on
in it, but it's not a liquid.

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It still will transmit certain
types of waves that liquids

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won't.

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And this is called
the asthenosphere,

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kind of this jelly, putty layer.

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And it's like that
because it's so hot

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that the rock has
somewhat melted.

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So this layer right here in
magenta is the asthenosphere.

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I've seen some spellings where
there's an "e" after the "a."

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I think that's maybe
the European spelling.

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And the asthenosphere
obviously starts right

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below the lithosphere.

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It's what the
lithospheric plates-- when

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we talk about plate tectonics--
are riding on top of.

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It's kind of the
gummy material that

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allows it to actually move,
that allows the rigid layer

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to actually move on top.

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So it starts below
the lithosphere,

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and it ends at around
660 kilometers deep.

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So this right here is
660 kilometers deep.

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And then you go even
deeper than that,

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and now the pressures
are so big that even

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though the temperatures
are even higher

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the pressures are so big
that the same material can't

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have fluid motion anymore.

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It's essentially
been jammed together.

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So you can imagine if you have
things that are somewhat fluid,

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that means that the
molecules can kind of slide

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past each other,
maybe very slowly.

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But if you increase
the pressure enough

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they'll be jammed
into each other.

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And that's essentially
what happens

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in the next layer of the mantle.

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All of these layers
of the mantle

00:08:47.860 --> 00:08:49.140
are made up of the same thing.

00:08:49.140 --> 00:08:51.680
It's just difference of
temperature and pressure.

00:08:51.680 --> 00:08:53.180
And so that next
layer of the mantle

00:08:53.180 --> 00:08:54.221
is called the mesosphere.

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This is called the
mesosphere, but there's also

00:09:03.840 --> 00:09:06.050
a layer of our atmosphere,
the layer right

00:09:06.050 --> 00:09:08.220
above the stratosphere
that's called the mesosphere,

00:09:08.220 --> 00:09:09.780
and so don't get confused here.

00:09:09.780 --> 00:09:11.570
These are two
different mesospheres.

00:09:11.570 --> 00:09:13.980
And this layer, the
pressure is so big

00:09:13.980 --> 00:09:15.840
that now we are rigid again.

00:09:15.840 --> 00:09:18.380
We are kind of definitely solid.

00:09:18.380 --> 00:09:20.040
None of this debate
about a little bit

00:09:20.040 --> 00:09:22.650
of fluid motion because
the pressures are so big.

00:09:22.650 --> 00:09:26.310
Now, you go a little
bit deeper, we are now

00:09:26.310 --> 00:09:30.500
in the core, the metallic
core, and the temperatures are

00:09:30.500 --> 00:09:34.380
so high that even though the
pressures are high, because we

00:09:34.380 --> 00:09:36.190
have a compositional
change, we're

00:09:36.190 --> 00:09:40.030
at pressures where this type
of mesospheric rock is rigid,

00:09:40.030 --> 00:09:44.730
but metals at these temperatures
actually can be fluid,

00:09:44.730 --> 00:09:45.870
can actually be liquid.

00:09:45.870 --> 00:09:51.680
And so we actually have
a liquid outer core.

00:09:55.990 --> 00:09:57.900
The entire core,
as far as we know,

00:09:57.900 --> 00:09:59.260
is made up of the same stuff.

00:09:59.260 --> 00:10:01.840
Just the outer part of
the core, the temperatures

00:10:01.840 --> 00:10:04.550
are high enough
to melt the metal,

00:10:04.550 --> 00:10:07.210
but the pressures aren't so
high enough to make them solid.

00:10:07.210 --> 00:10:08.560
The pressures are
definitely high enough

00:10:08.560 --> 00:10:10.018
to make kind of
more rocky material

00:10:10.018 --> 00:10:11.690
solid, but not the metals.

00:10:11.690 --> 00:10:14.350
And then you go even deeper,
now even though the temperature

00:10:14.350 --> 00:10:16.760
keeps going up, the
pressure is so strong

00:10:16.760 --> 00:10:18.800
that even the metals are solid.

00:10:18.800 --> 00:10:23.229
So this is the solid inner core.

00:10:23.229 --> 00:10:25.270
So when you think about
the mechanical properties

00:10:25.270 --> 00:10:28.950
the innermost-- And just so
you know the total distances

00:10:28.950 --> 00:10:32.720
we're talking about, the outer
core starts at-- Actually I

00:10:32.720 --> 00:10:34.740
didn't tell you where
the mesosphere--

00:10:34.740 --> 00:10:40.240
So the mantle ends at about
2,900 kilometers deep.

00:10:40.240 --> 00:10:42.780
So that's clearly where the
mesosphere ends as well,

00:10:42.780 --> 00:10:46.250
because the mesosphere is
kind of the lower mantle.

00:10:46.250 --> 00:10:49.760
So this is 2,900
kilometers deep.

00:10:49.760 --> 00:10:52.660
Then you go even deeper, you're
in the liquid outer core.

00:10:52.660 --> 00:10:55.290
And that extends from
about 2,900 kilometers

00:10:55.290 --> 00:10:59.120
deep to about 5,100
kilometers deep.

00:10:59.120 --> 00:11:02.290
So I frankly should
make the liquid core

00:11:02.290 --> 00:11:04.300
in my drawing even wider.

00:11:04.300 --> 00:11:10.562
So this depth right over here
is about 5,100 kilometers deep.

00:11:10.562 --> 00:11:13.020
And then, obviously, then you
have the center of the earth,

00:11:13.020 --> 00:11:14.930
and the entire
radius of the earth

00:11:14.930 --> 00:11:18.560
is about 6,400 kilometers.

00:11:18.560 --> 00:11:20.200
So hopefully that
clarifies things

00:11:20.200 --> 00:11:22.630
when you hear people talking
about the lithosphere,

00:11:22.630 --> 00:11:23.770
or the mantle.

00:11:23.770 --> 00:11:26.370
They're really talking about
mechanical versus composition.

00:11:26.370 --> 00:11:28.890
When we talk about
mechanical solid inner core,

00:11:28.890 --> 00:11:32.920
liquid outer core,
essentially solid mesosphere.

00:11:32.920 --> 00:11:33.710
It's rigid.

00:11:33.710 --> 00:11:37.810
Then you have something kind of
a spongy, somewhat fluid, not

00:11:37.810 --> 00:11:40.930
solid, not liquid asthenosphere
that the lithospheric plates

00:11:40.930 --> 00:11:42.030
can ride on top of.

00:11:42.030 --> 00:11:44.610
And then you have your actual
rigid, solid lithosphere

00:11:44.610 --> 00:11:49.263
made up of the uppermost part
of the mantle and the crust.


Hawaiian islands formation

WEBVTT
Kind: captions
Language: en

00:00:00.550 --> 00:00:03.510
We've talked a lot about
the formations of mountains

00:00:03.510 --> 00:00:06.080
and volcanoes when plates
are running into each other,

00:00:06.080 --> 00:00:09.290
or when one plate is being
subducted under another.

00:00:09.290 --> 00:00:10.930
But that isn't
the only place, it

00:00:10.930 --> 00:00:13.430
is the dominant place
or the most likely place

00:00:13.430 --> 00:00:16.349
to find mountains and volcanoes
on the surface of the Earth,

00:00:16.349 --> 00:00:18.890
but that's not the only place
that mountains or volcanoes can

00:00:18.890 --> 00:00:19.390
form.

00:00:19.390 --> 00:00:22.900
And probably the biggest
example of volcanic activity,

00:00:22.900 --> 00:00:24.400
or the most popular
one-- this might

00:00:24.400 --> 00:00:27.480
be a slightly American,
Amerocentric point of view,

00:00:27.480 --> 00:00:31.510
but the most often cited
example of volcanic activity

00:00:31.510 --> 00:00:34.075
away from a plate
boundary is Hawaii.

00:00:36.960 --> 00:00:39.980
So this right here, these
are the Hawaiian Islands.

00:00:39.980 --> 00:00:43.110
This is the big
island of Hawaii,

00:00:43.110 --> 00:00:48.020
and it is experiencing
an active volcano.

00:00:48.020 --> 00:00:51.130
Lava or magma is flowing
from underneath the ground,

00:00:51.130 --> 00:00:53.170
and once it surfaces
we call it lava.

00:00:53.170 --> 00:00:59.360
And that lava is actively
making the island bigger.

00:00:59.360 --> 00:01:02.250
So where is that volcanic
activity coming from?

00:01:02.250 --> 00:01:04.599
And then how can we think
about that volcanic activity

00:01:04.599 --> 00:01:08.680
or that kind of heat rising from
below the surface of the Earth

00:01:08.680 --> 00:01:11.380
to explain some of the
geological features we

00:01:11.380 --> 00:01:13.700
see around Hawaii?

00:01:13.700 --> 00:01:15.850
So what we think is happening,
and once again, this

00:01:15.850 --> 00:01:18.500
is all theory right
here, is that Hawaii

00:01:18.500 --> 00:01:21.460
is sitting on top of a hot
spot, and in particular,

00:01:21.460 --> 00:01:24.880
the big island of Hawaii is
sitting on top of the hot spot

00:01:24.880 --> 00:01:26.140
right now.

00:01:26.140 --> 00:01:29.870
And this hot spot,
there's different ways,

00:01:29.870 --> 00:01:31.790
different theories on
how it might emerge.

00:01:31.790 --> 00:01:35.640
But we think that at the
mantle core boundary--

00:01:35.640 --> 00:01:37.890
and I don't know in this
diagram whether they intended

00:01:37.890 --> 00:01:40.010
this white area to be
the core, but let's just

00:01:40.010 --> 00:01:43.020
say that this is the
outer core down here.

00:01:43.020 --> 00:01:46.640
Let's just say that
this is the outer core

00:01:46.640 --> 00:01:50.630
for the sake of
explaining things.

00:01:50.630 --> 00:01:59.120
It's possible that just based
on the fluid dynamics of what's

00:01:59.120 --> 00:02:01.840
happening at that mantle
outer core boundary,

00:02:01.840 --> 00:02:06.576
that plumes of really hot
material can kind of rise up.

00:02:06.576 --> 00:02:07.950
Let me do this in
a darker color.

00:02:07.950 --> 00:02:12.610
They could rise up
from the outer core,

00:02:12.610 --> 00:02:16.220
and then create hot spots
underneath the moving

00:02:16.220 --> 00:02:19.120
lithospheric plates.

00:02:19.120 --> 00:02:21.930
Now, we don't know for sure
whether the hot spots are being

00:02:21.930 --> 00:02:27.010
created by these mantle plumes,
these material formed or heated

00:02:27.010 --> 00:02:29.020
up at the outer core
mantle boundary.

00:02:29.020 --> 00:02:30.920
But what we do feel
pretty confident about

00:02:30.920 --> 00:02:33.630
is that there is
this hot spot here,

00:02:33.630 --> 00:02:37.490
and it's independent of any
of those convection patterns

00:02:37.490 --> 00:02:37.990
that we saw.

00:02:37.990 --> 00:02:39.156
I shouldn't say independent.

00:02:39.156 --> 00:02:40.850
It's obviously all
related because we

00:02:40.850 --> 00:02:43.480
have all this fluidic motion
going on in the mantle,

00:02:43.480 --> 00:02:47.339
but it's separate on some degree
from all of those convection

00:02:47.339 --> 00:02:49.380
patterns that we talked
about that would actually

00:02:49.380 --> 00:02:51.310
cause the plates to move.

00:02:51.310 --> 00:02:53.260
And to a large
degree, or the way

00:02:53.260 --> 00:02:55.960
we think about it right
now, this is stationary,

00:02:55.960 --> 00:03:01.210
this hot spot is stationary
relative to the plates.

00:03:01.210 --> 00:03:03.600
And the reason why we feel
pretty good about thinking

00:03:03.600 --> 00:03:06.280
that it's stationary
relative to the plates

00:03:06.280 --> 00:03:08.250
is we see this
notion right here,

00:03:08.250 --> 00:03:13.400
if you look at the volcanic
rock in Kauai, which

00:03:13.400 --> 00:03:18.020
is one of the older inhabited
Hawaiian Islands, the oldest

00:03:18.020 --> 00:03:22.970
rocks that we've observed
there is 5.5 million years old,

00:03:22.970 --> 00:03:24.534
and it's all volcanic rock.

00:03:24.534 --> 00:03:26.200
Now, the oldest
volcanic rock that we've

00:03:26.200 --> 00:03:30.810
observed on the big island
is about 700,000 years old.

00:03:30.810 --> 00:03:34.730
We also know that
the Pacific Plate,

00:03:34.730 --> 00:03:36.950
you could look at this
diagram right over here,

00:03:36.950 --> 00:03:40.090
is moving in this
general direction.

00:03:40.090 --> 00:03:43.320
We know it from
GPS measurements.

00:03:43.320 --> 00:03:46.910
It's moving exactly
in the direction

00:03:46.910 --> 00:03:51.920
that the Hawaiian Islands
are kind of a distributed in.

00:03:51.920 --> 00:03:55.100
So frankly, the only
good explanation

00:03:55.100 --> 00:03:58.260
for why we see this pattern,
why we see newer land here,

00:03:58.260 --> 00:04:01.100
and then as we go further and
further up the Hawaiian Island

00:04:01.100 --> 00:04:02.620
chain we see older
and older land,

00:04:02.620 --> 00:04:05.630
and actually if
we keep going, we

00:04:05.630 --> 00:04:07.470
have the Leeward
Islands over here.

00:04:07.470 --> 00:04:10.350
And as we keep measuring the
rock on the Leeward Islands

00:04:10.350 --> 00:04:13.660
they get older and older
as you go to the Northwest.

00:04:13.660 --> 00:04:16.680
And then if you even look
at what's below the ocean,

00:04:16.680 --> 00:04:18.110
this is the big
island of Hawaii,

00:04:18.110 --> 00:04:19.610
these are the main
Hawaiian Islands,

00:04:19.610 --> 00:04:20.990
these are the Leeward Islands.

00:04:20.990 --> 00:04:24.010
But you see even beyond that
submersed under the Pacific

00:04:24.010 --> 00:04:27.620
Ocean you continue to
see a chain of islands.

00:04:27.620 --> 00:04:30.520
So the explanation for
what's happening here

00:04:30.520 --> 00:04:33.280
is that you have a
stationary hot spot that

00:04:33.280 --> 00:04:37.790
is right now underneath
the big island of Hawaii.

00:04:37.790 --> 00:04:39.880
And I just want to be
clear, the big island

00:04:39.880 --> 00:04:41.500
is called the island of Hawaii.

00:04:41.500 --> 00:04:44.050
It is one of the islands
in the state of Hawaii.

00:04:44.050 --> 00:04:45.830
So I don't want to
cause you confusion.

00:04:45.830 --> 00:04:49.210
I'll just call it the big
island from here on out.

00:04:49.210 --> 00:04:51.650
So the hot spot is right
under the big island.

00:04:51.650 --> 00:04:57.450
But if you were to rewind
5 million years ago,

00:04:57.450 --> 00:05:02.100
the entire Pacific
Plate was probably

00:05:02.100 --> 00:05:04.990
on the order of about
150 to 200 miles,

00:05:04.990 --> 00:05:08.020
however far Kauai is
from the big island,

00:05:08.020 --> 00:05:11.390
it was probably shifted
that much to the southeast

00:05:11.390 --> 00:05:13.820
if you go back 5
million years ago.

00:05:13.820 --> 00:05:15.750
So 5 million years
ago, when all of this

00:05:15.750 --> 00:05:18.700
was shifted down and
to the right, then

00:05:18.700 --> 00:05:22.390
Kauai was on top
of the hot spot.

00:05:22.390 --> 00:05:25.220
And so this is how each of
these islands are formed.

00:05:25.220 --> 00:05:29.059
If you rewind a ton of years
then maybe this area over here

00:05:29.059 --> 00:05:30.850
on the Pacific Plate
was over the hot spot.

00:05:30.850 --> 00:05:32.750
An island formed there.

00:05:32.750 --> 00:05:35.900
Then the Pacific Plate kept
moving to the Northwest.

00:05:35.900 --> 00:05:39.760
It kept moving to the Northwest,
and new islands, new volcanoes

00:05:39.760 --> 00:05:40.340
kept forming.

00:05:40.340 --> 00:05:43.440
Those volcanoes would release
lava that would keep piling up,

00:05:43.440 --> 00:05:45.910
keep piling up, keep
piling up, eventually go

00:05:45.910 --> 00:05:48.060
above the surface of
the water and form

00:05:48.060 --> 00:05:49.250
this whole chain of islands.

00:05:49.250 --> 00:05:52.080
And as the whole Pacific Plate
kept moving to the Northwest,

00:05:52.080 --> 00:05:54.420
it kept forming new islands.

00:05:54.420 --> 00:05:55.980
Now, the one question
you might ask

00:05:55.980 --> 00:05:59.580
is, well, how come the
big island is bigger?

00:05:59.580 --> 00:06:01.440
Has a plate kind of
paused over there?

00:06:01.440 --> 00:06:03.510
Is it spending more
time over the hot spot

00:06:03.510 --> 00:06:08.720
so that more lava can kind
of form there to form this?

00:06:08.720 --> 00:06:10.960
Essentially, it's an
underwater mountain

00:06:10.960 --> 00:06:12.850
that's now also above the water.

00:06:12.850 --> 00:06:15.530
And actually if you go from
the base of the Pacific Ocean

00:06:15.530 --> 00:06:18.500
to the top of the
big island of Hawaii,

00:06:18.500 --> 00:06:20.590
it's actually 50% higher
than Mount Everest.

00:06:20.590 --> 00:06:22.450
So you could really just
view it as a big mountain.

00:06:22.450 --> 00:06:24.820
But the question is this looks
so much bigger than Kauai,

00:06:24.820 --> 00:06:26.319
and they keep getting
smaller as you

00:06:26.319 --> 00:06:27.620
keep going to the Northwest.

00:06:27.620 --> 00:06:29.610
Is it somehow the
Pacific Plate slowing?

00:06:29.610 --> 00:06:32.030
Is it spending more time here?

00:06:32.030 --> 00:06:34.140
And the answer is it's
probably not slowing.

00:06:34.140 --> 00:06:37.750
What's happening is at one time
Kauai was also probably also

00:06:37.750 --> 00:06:39.700
a relatively large island.

00:06:39.700 --> 00:06:42.520
If you rewind maybe
5 million years ago

00:06:42.520 --> 00:06:45.390
Kauai also might have
been about that big.

00:06:45.390 --> 00:06:47.800
But over 5 million
years it's just

00:06:47.800 --> 00:06:49.801
experienced a ton of erosion.

00:06:49.801 --> 00:06:52.050
Remember, once it moved over
the hot spot and new land

00:06:52.050 --> 00:06:54.797
wasn't being created it's in
the middle of the Pacific Ocean.

00:06:54.797 --> 00:06:55.880
It's experiencing weather.

00:06:55.880 --> 00:06:58.250
5 million years is a
long period of time.

00:06:58.250 --> 00:07:00.110
And so it just got
eroded over that time.

00:07:00.110 --> 00:07:03.320
So the older the island is, the
more eroded it's going to be,

00:07:03.320 --> 00:07:04.800
and the smaller
it's going to be.

00:07:04.800 --> 00:07:07.541
So if you go to these
underwater mountains

00:07:07.541 --> 00:07:10.040
up here that don't even surface
above the ocean, at one time

00:07:10.040 --> 00:07:13.030
they might have surfaced, but
due to the ocean and weather

00:07:13.030 --> 00:07:15.060
and whatnot they've just
been eroded over time

00:07:15.060 --> 00:07:19.662
to become smaller and smaller
kind of remnants of volcanoes.

00:07:19.662 --> 00:07:21.120
So anyway, I thought
you would find

00:07:21.120 --> 00:07:24.720
that entertaining of how the
Hawaiian Islands actually got

00:07:24.720 --> 00:07:26.220
formed, and how we
can actually have

00:07:26.220 --> 00:07:29.140
these hot spots, and
this volcanic activity,

00:07:29.140 --> 00:07:30.740
and actually even
earthquake activity

00:07:30.740 --> 00:07:34.764
outside of actual
plate boundaries.

00:07:34.764 --> 00:07:36.680
Actually, while we're
looking at this diagram,

00:07:36.680 --> 00:07:39.330
we talked about the trenches
at plate boundaries.

00:07:39.330 --> 00:07:42.020
You can actually see it here
because this shows the depth.

00:07:42.020 --> 00:07:44.370
And the really dark,
dark, dark, dark blue

00:07:44.370 --> 00:07:46.840
is really deep
parts of the ocean.

00:07:46.840 --> 00:07:48.920
So this right here is
the Mariana Trench.

00:07:48.920 --> 00:07:51.030
And you can see over here
the Pacific Plate just

00:07:51.030 --> 00:07:52.420
getting abducted.

00:07:52.420 --> 00:07:55.340
Or not abducted, getting
subducted into other plates

00:07:55.340 --> 00:07:57.890
underneath and forms
these trenches here.

00:07:57.890 --> 00:08:00.420
Anyway, hopefully you
found that entertaining.


Plates moving due to convection in mantle

WEBVTT
Kind: captions
Language: en

00:00:00.234 --> 00:00:01.650
What I want to do
in this video is

00:00:01.650 --> 00:00:05.600
talk a little bit about maybe
why the plates are actually

00:00:05.600 --> 00:00:06.979
moving in the first place.

00:00:06.979 --> 00:00:08.770
And nothing I'm talking
about in this video

00:00:08.770 --> 00:00:10.780
has been definitively proved.

00:00:10.780 --> 00:00:14.630
This is just kind of the current
thinking, the leading thinking,

00:00:14.630 --> 00:00:16.682
on why plates are
actually moving.

00:00:16.682 --> 00:00:18.890
Although we haven't seen
the definitive evidence yet,

00:00:18.890 --> 00:00:21.380
and it's probably a combination
of a bunch of things.

00:00:21.380 --> 00:00:23.050
Now, before we even
talk about plates,

00:00:23.050 --> 00:00:25.180
let's just talk
about convection.

00:00:25.180 --> 00:00:27.640
And you might already be
familiar with the term,

00:00:27.640 --> 00:00:29.500
but just in case
you're not, let's do

00:00:29.500 --> 00:00:31.370
a little bit of
review of convection.

00:00:31.370 --> 00:00:34.600
So let's say I have
a pot over here.

00:00:34.600 --> 00:00:36.280
So that is my pot.

00:00:36.280 --> 00:00:39.520
And it contains some water.

00:00:39.520 --> 00:00:42.850
So I have water in my pot.

00:00:42.850 --> 00:00:45.610
And let's say I only
heat one end of the pot.

00:00:45.610 --> 00:00:47.970
So I put a flame right over
at that end of the pot.

00:00:47.970 --> 00:00:49.410
So what's going to happen?

00:00:49.410 --> 00:00:53.070
Well, the water that's
right over the flame

00:00:53.070 --> 00:00:55.980
is going to be warmed up more
than any of the other water.

00:00:55.980 --> 00:01:00.200
So this water is
going to get warm.

00:01:00.200 --> 00:01:03.010
But when it gets warm, it
also becomes less dense.

00:01:03.010 --> 00:01:05.550
When you have a fluid,
if you warm it up,

00:01:05.550 --> 00:01:07.800
the molecules are
vibrating more.

00:01:07.800 --> 00:01:09.400
They have more kinetic energy.

00:01:09.400 --> 00:01:11.600
They're going to a bounce
further distances away

00:01:11.600 --> 00:01:12.270
from each other.

00:01:12.270 --> 00:01:13.967
They will become less dense.

00:01:13.967 --> 00:01:15.800
And if you have something
that's less dense,

00:01:15.800 --> 00:01:17.883
and it's surrounded by
things that are more dense,

00:01:17.883 --> 00:01:20.930
and we're dealing in kind
of a fluid state right here,

00:01:20.930 --> 00:01:25.760
that warm, less dense water
is going to move upwards.

00:01:25.760 --> 00:01:27.770
It's going to move upwards.

00:01:27.770 --> 00:01:32.470
Well, when it moves upwards
something has to replace it.

00:01:32.470 --> 00:01:35.270
So you're going to
have cooler water

00:01:35.270 --> 00:01:37.350
from this side of the
container kind of replacing

00:01:37.350 --> 00:01:39.040
where that water was.

00:01:39.040 --> 00:01:44.200
Now, this water, as it rises,
what's going to happen to it?

00:01:44.200 --> 00:01:45.450
Well, it's going to cool down.

00:01:45.450 --> 00:01:46.750
It's going to get
further from the flame.

00:01:46.750 --> 00:01:48.958
It's going to mix with maybe
some of the other water,

00:01:48.958 --> 00:01:52.580
or transfer some of
its kinetic energy

00:01:52.580 --> 00:01:54.390
to the neighboring water.

00:01:54.390 --> 00:01:55.910
So it'll cool down.

00:01:55.910 --> 00:01:58.820
But once it cools down,
what's it going to want to do?

00:01:58.820 --> 00:02:01.650
Remember, in general, the
closer you are to the flame.

00:02:01.650 --> 00:02:04.460
So the water closer to
the flame in general

00:02:04.460 --> 00:02:05.550
is going to be warmer.

00:02:05.550 --> 00:02:07.341
So all of this stuff
is going to be warmer,

00:02:07.341 --> 00:02:09.820
and all of this stuff up
here, like the coldest water,

00:02:09.820 --> 00:02:12.340
is always going to be
furthest from the flame.

00:02:12.340 --> 00:02:14.980
And so the coldest water
is going to be over here.

00:02:14.980 --> 00:02:18.030
But remember, the coldest water
is also the densest water.

00:02:18.030 --> 00:02:21.670
So this water over
here is dense.

00:02:21.670 --> 00:02:23.050
And so it will sink.

00:02:23.050 --> 00:02:24.612
It's denser than
the water around it.

00:02:24.612 --> 00:02:26.070
And it also helps
replace the water

00:02:26.070 --> 00:02:28.112
that's going here to
get warmed up again.

00:02:28.112 --> 00:02:30.070
And so what you do is
you have this cycle here.

00:02:30.070 --> 00:02:33.320
Warm water rises, moves
over to the right down here,

00:02:33.320 --> 00:02:36.140
and then goes back down as it
cools down, and it's dense,

00:02:36.140 --> 00:02:37.570
and then it gets
warmed up again.

00:02:37.570 --> 00:02:40.850
And so this process,
essentially what it's doing

00:02:40.850 --> 00:02:43.340
is it's transferring the heat.

00:02:43.340 --> 00:02:46.020
It's allowing the heat to be
transferred from this one spot

00:02:46.020 --> 00:02:48.070
throughout the fluid.

00:02:48.070 --> 00:02:54.630
And so we call this
process, this is convection.

00:02:54.630 --> 00:02:57.600
Now, the reason why we
think the plates are moving

00:02:57.600 --> 00:03:01.370
is because we think that there
are similar types of convection

00:03:01.370 --> 00:03:05.240
currents in the
asthenosphere, in the mantle,

00:03:05.240 --> 00:03:07.930
in the more fluid
part of the mantle.

00:03:07.930 --> 00:03:11.870
Remember, most of the mantle
you can kind of view it

00:03:11.870 --> 00:03:16.260
as this mooshy, spongy, not
quite liquid, but not quite

00:03:16.260 --> 00:03:18.060
solid state, kind of plastic.

00:03:18.060 --> 00:03:21.030
It can kind of moosh past.

00:03:21.030 --> 00:03:29.080
It can kind of flow like super,
super, super thick, like super

00:03:29.080 --> 00:03:30.130
viscous fluid.

00:03:30.130 --> 00:03:32.400
So not quite solid,
not quite liquid.

00:03:32.400 --> 00:03:34.180
But the same thing
could be happening.

00:03:34.180 --> 00:03:37.209
You have certain areas
in the mantle that

00:03:37.209 --> 00:03:39.000
are hotter than others,
and this particular

00:03:39.000 --> 00:03:40.390
in the asthenosphere.

00:03:40.390 --> 00:03:42.100
And those areas,
that's where you're

00:03:42.100 --> 00:03:46.670
going to have the material
in the mantle move

00:03:46.670 --> 00:03:50.060
up, because it's
hotter, it's less dense,

00:03:50.060 --> 00:03:51.610
and it will move up.

00:03:51.610 --> 00:03:54.260
And maybe it'll cause one
of these divergent rifts

00:03:54.260 --> 00:04:00.000
where kind of plate material
and crustal material is forming.

00:04:00.000 --> 00:04:06.650
And then as it moves
up, it cools down,

00:04:06.650 --> 00:04:13.080
and eventually sinks, only
to get heated up again.

00:04:13.080 --> 00:04:14.830
So it has this kind
of circular motion

00:04:14.830 --> 00:04:17.380
just like we saw with
the boiling water.

00:04:17.380 --> 00:04:20.500
And so that process, remember
this isn't completely liquid.

00:04:20.500 --> 00:04:21.459
It is rocky.

00:04:21.459 --> 00:04:24.200
So it's going to
potentially be able to take

00:04:24.200 --> 00:04:25.140
other things with it.

00:04:25.140 --> 00:04:29.760
It could maybe drag the
crust along with it.

00:04:29.760 --> 00:04:32.404
Or I should say it could
drag the lithosphere along

00:04:32.404 --> 00:04:33.570
with it, not just the crust.

00:04:33.570 --> 00:04:37.130
It could drag all this rigid
rock up here along with it,

00:04:37.130 --> 00:04:41.520
causing it to move in
that general direction.

00:04:41.520 --> 00:04:42.800
So you have the drag there.

00:04:42.800 --> 00:04:45.340
You could also imagine this
kind of a suction effect,

00:04:45.340 --> 00:04:47.060
where, if you view
it as a fluid,

00:04:47.060 --> 00:04:49.180
you have a bunch of
fluid coming down here.

00:04:49.180 --> 00:04:51.380
So it would kind of pull
the lithosphere down

00:04:51.380 --> 00:04:57.130
at those points, and it would
kind of push the lithosphere up

00:04:57.130 --> 00:04:58.300
at those points.

00:04:58.300 --> 00:05:01.770
So you have these
convection currents

00:05:01.770 --> 00:05:04.790
that are essentially driving it.

00:05:04.790 --> 00:05:07.710
These aren't going to be super
fast moving fluid convection

00:05:07.710 --> 00:05:09.800
currents, like you would
expect with boiling water

00:05:09.800 --> 00:05:11.180
or with heated water.

00:05:11.180 --> 00:05:13.350
These would be slow moving
convection currents,

00:05:13.350 --> 00:05:15.540
but they're moving
enough, and they're

00:05:15.540 --> 00:05:18.650
able to kind of put enough
drag on the lithosphere

00:05:18.650 --> 00:05:21.240
to take the lithosphere
along with it.

00:05:21.240 --> 00:05:23.380
And so that's kind
of at a high level

00:05:23.380 --> 00:05:26.000
the dominant theory as
to why they're moving.

00:05:26.000 --> 00:05:28.200
There's other ones
that talk about maybe

00:05:28.200 --> 00:05:33.780
these lithospheric plates,
they kind of thicken

00:05:33.780 --> 00:05:36.870
as they move further
away from this area

00:05:36.870 --> 00:05:38.640
where the ridge is forming.

00:05:38.640 --> 00:05:41.380
And if we look at this
oceanic crust right over here.

00:05:41.380 --> 00:05:44.670
And so over time,
they're denser over here,

00:05:44.670 --> 00:05:49.390
because there's more cooled
down material at these points.

00:05:49.390 --> 00:05:51.555
And it's already
a little bit lower

00:05:51.555 --> 00:05:53.930
because this is where a lot
of the land is being created.

00:05:53.930 --> 00:05:56.030
And so there's maybe some
gravitational effects.

00:05:56.030 --> 00:05:57.760
But the dominant
effect, we think,

00:05:57.760 --> 00:06:02.160
is due to this convection
in the upper mantle.


Plate Tectonics-- Geological features of Convergent Plate Boundaries

WEBVTT
Kind: captions
Language: en

00:00:00.335 --> 00:00:02.743
We've already talked a lot about plate boundaries

00:00:02.743 --> 00:00:09.546
where essentially new crust material is being created and the plates are actually moving apart -

00:00:09.546 --> 00:00:15.336
we call these divergent boundaries, and the example we showed of this was the Mid-Atlantic Ridge

00:00:15.336 --> 00:00:19.199
where essentially new crustal material is being created.

00:00:19.199 --> 00:00:24.151
Now, on the other side of the equation you have areas where plates are ramming into each other.

00:00:24.151 --> 00:00:28.807
We see that over here where the Nazca plate is running into the South American plate.

00:00:28.807 --> 00:00:38.466
We see it over here where the Pacific plate is running into the Filipino plate - they're running into each other.

00:00:38.466 --> 00:00:43.384
So what happens over there? So what we're gonna do is just go through the different scenarios.

00:00:43.384 --> 00:00:48.121
The general idea is that one plate is going to get subducted under another.

00:00:48.121 --> 00:00:52.446
Tthey're ramming into each other, one is going to get essentially pushed under the other one.

00:00:52.446 --> 00:00:55.412
This diagram shows some subduction over here.

00:00:55.412 --> 00:01:00.158
Tthis is essentially an oceanic plate being subducted under another oceanic plate,

00:01:00.158 --> 00:01:06.134
so not too different than what might happen when the Pacific plate runs into the Filipino plate

00:01:06.134 --> 00:01:09.954
right over here, then on this side of the diagram

00:01:09.954 --> 00:01:18.069
we see an oceanic plate and the oceanic crust getting subducted under a continental plate, right over here.

00:01:18.069 --> 00:01:24.126
And this is what's happening when the Nazca plate is getting subducted under the South American plate

00:01:24.126 --> 00:01:26.238
and when that happens you have a couple of things

00:01:26.238 --> 00:01:29.383
so you have the oceanic plate being pushed under

00:01:29.383 --> 00:01:36.010
and what happens at the same time the continental plate gets pushed upwards causing mountain ranges like The Andes

00:01:36.010 --> 00:01:39.674
and that's exactly what causes - what has created The Andes,

00:01:39.674 --> 00:01:46.953
it's the upward force from the Nazca plate being pushed under the South American plate at that coast line.

00:01:46.953 --> 00:01:52.956
And what you're also going to see is, and if you can imagine you have these huge plates grinding past each other,

00:01:52.956 --> 00:01:59.628
it's not a very smooth process, every now and then you reach a breaking point where huge amount of energy

00:01:59.628 --> 00:02:03.823
get released so you're also going to see a lot of earthquakes in those areas

00:02:03.823 --> 00:02:06.878
and we know that Chile has a lot of earthquakes.

00:02:06.878 --> 00:02:10.538
And then on top of that, this is going to result in a lot of heat

00:02:10.538 --> 00:02:14.472
and a lot of friction of the plates grinding past each other

00:02:14.472 --> 00:02:20.960
essentially allowing magma to form at that part of the rock

00:02:20.960 --> 00:02:25.625
and because it's getting so heated you also have volcanoes in these areas

00:02:25.625 --> 00:02:30.829
where essentially something is being subducted underneath a continental plate.

00:02:30.829 --> 00:02:33.939
Now, we also talked about what's happening in the Pacific

00:02:33.939 --> 00:02:38.602
where we have the Pacific plate being subducted under the Filipino plate.

00:02:38.602 --> 00:02:41.812
That's what we keep referring to over here.

00:02:41.812 --> 00:02:44.266
And that's doing a couple of interesting things.

00:02:44.266 --> 00:02:46.410
So whenever you have subduction, you have trenches.

00:02:46.410 --> 00:02:48.279
But it's most interesting - or at least in my mind

00:02:48.279 --> 00:02:54.899
that the deepest trenches have been created where you have an oceanic plate being subducted under another oceanic plate.

00:02:54.899 --> 00:02:56.909
So a couple of things are going to happen.

00:02:56.909 --> 00:03:01.087
You're going to have deep trenches form,

00:03:01.087 --> 00:03:04.282
over here you see in this diagram we also have a trench and the first example,

00:03:04.282 --> 00:03:08.673
but you have trenches form where one oceanic plate is being subducted under another

00:03:08.673 --> 00:03:12.406
and then you have that same type of friction that you saw over here create volcanoes

00:03:12.406 --> 00:03:15.812
and those volcanoes will initially be underwater volcanoes

00:03:15.812 --> 00:03:23.003
since these are both oceanic plates, or we're dealing with oceanic crust at that point of the plate,

00:03:23.003 --> 00:03:24.939
it doesn't have to be entirely and oceanic plate,

00:03:24.939 --> 00:03:27.407
and there'll first be underwater volcanoes

00:03:27.407 --> 00:03:32.141
but as the lave piles up and hardens, it'll eventually turn into a group of islands.

00:03:32.141 --> 00:03:37.474
And we've had that happening where the Pacific plate runs into the Filipino plate

00:03:37.474 --> 00:03:39.070
and first we have the trench,

00:03:39.070 --> 00:03:41.569
let me just draw everything right here.

00:03:41.569 --> 00:03:45.491
So, this is the boundary, roughly, roughly speaking

00:03:45.491 --> 00:03:47.343
this is the boundary between the two plates

00:03:47.343 --> 00:03:51.937
the Pacific plate and the Filipino plate right over here.

00:03:51.937 --> 00:03:55.320
And where it's being subducted you have the Mariana Trench

00:03:55.320 --> 00:03:57.968
which is the deepest trench in the world!

00:03:57.968 --> 00:04:04.151
It goes down 11 km - eleven thousand metres!

00:04:04.151 --> 00:04:06.891
That's deeper than Mount Everest is high.

00:04:06.891 --> 00:04:09.492
Mt Everest is about 9,000 metres high.

00:04:09.492 --> 00:04:12.737
And we'll see that's also due to another convergent plate boundary,

00:04:12.737 --> 00:04:15.288
another plate boundary where plates are running into each other.

00:04:15.288 --> 00:04:17.736
So not only do you see the Mariana Trench here

00:04:17.736 --> 00:04:20.173
because one plate is being subducted under the other,

00:04:20.173 --> 00:04:22.989
you see the formation of the Mariana Islands

00:04:22.989 --> 00:04:25.813
which were essentially created from underwater volcanoes

00:04:25.813 --> 00:04:28.606
because of all of the energy being released.

00:04:28.606 --> 00:04:34.670
And this is actually a depiction of what's the subduction that's happening at the Mariana Trench.

00:04:34.670 --> 00:04:38.066
You have the subduction over here then you have the Mriana Islands being created

00:04:38.066 --> 00:04:42.615
by essentially the energy causing magma and lava,

00:04:42.615 --> 00:04:46.383
essentially magma before it surfaces, to flow on the top

00:04:46.383 --> 00:04:49.495
and as lava just goes and starts building these islands.

00:04:49.495 --> 00:04:52.290
Now, the last type of convergent boundary

00:04:52.290 --> 00:04:57.139
is when you have two parts of continetal crust running into each other.

00:04:57.139 --> 00:05:04.222
So that's the situation that we have when the Indian plate is running into the Euroasian plate,

00:05:04.222 --> 00:05:06.782
I think you might already guess what's going to happen there.

00:05:06.782 --> 00:05:09.686
When you have two pieces of continetnal crust running into each other,

00:05:09.686 --> 00:05:12.496
one is more or less dense that the other.

00:05:12.496 --> 00:05:15.679
And so at least the crustal portions on them

00:05:15.679 --> 00:05:19.969
are just going keep jamming into each other.

00:05:19.969 --> 00:05:22.018
And so they're just going to push things up.

00:05:22.018 --> 00:05:25.689
This is a depiction righ here that I got from the USGS.

00:05:25.689 --> 00:05:31.277
And what's kind of depicting it - this is the Indian plate, this is the Euroasian plate,

00:05:31.277 --> 00:05:35.946
this is if you rewind a good bit before they really had the chance to jam into each other.

00:05:35.946 --> 00:05:39.936
But as they're jamming into each other, the Indian plate is kind of digging in a little bit,

00:05:39.936 --> 00:05:43.687
not being fully subducted, and it's causing the land to rise.

00:05:43.687 --> 00:05:49.799
And that essentially ends up with something like the Himalayas.

00:05:49.799 --> 00:05:55.483
This right here is a picture of Mount Everest which is almost 9,000 metres high,

00:05:55.483 --> 00:05:58.206
9,000 metres above sea level.

00:05:58.206 --> 00:06:02.206
So, it's almost as high as the Mariana Trench is deep.


Plate tectonics: Difference between crust and lithosphere

WEBVTT
Kind: captions
Language: en

00:00:00.304 --> 00:00:02.470
What I want to do in this
video is talk a little bit

00:00:02.470 --> 00:00:03.750
about plate tectonics.

00:00:06.620 --> 00:00:08.370
And you've probably
heard the word before,

00:00:08.370 --> 00:00:10.040
and are probably,
or you might be

00:00:10.040 --> 00:00:13.630
somewhat familiar with
what it discusses.

00:00:13.630 --> 00:00:19.360
And it's really just the idea
that the surface of the Earth

00:00:19.360 --> 00:00:22.620
is made up of a bunch
of these rigid plates.

00:00:22.620 --> 00:00:25.390
So it's broken up into
a bunch of rigid plates,

00:00:25.390 --> 00:00:28.950
and these rigid plates move
relative to each other.

00:00:28.950 --> 00:00:30.860
They move relative to
each other and take

00:00:30.860 --> 00:00:32.740
everything that's
on them for a ride.

00:00:32.740 --> 00:00:36.610
And the things that are on
them include the continents.

00:00:36.610 --> 00:00:39.830
So it literally is talking about
the movement of these plates.

00:00:39.830 --> 00:00:42.720
And over here I have
a picture I got off

00:00:42.720 --> 00:00:45.600
of Wikipedia of
the actual plates.

00:00:45.600 --> 00:00:47.440
And over here you have
the Pacific Plate.

00:00:47.440 --> 00:00:48.490
Let me do that in
a darker color.

00:00:48.490 --> 00:00:49.400
You have the Pacific Plate.

00:00:49.400 --> 00:00:50.527
You have a Nazca Plate.

00:00:50.527 --> 00:00:51.860
You have a South American Plate.

00:00:51.860 --> 00:00:52.540
I could keep going on.

00:00:52.540 --> 00:00:53.580
You have an Antarctic Plate.

00:00:53.580 --> 00:00:55.016
It's actually,
obviously whenever

00:00:55.016 --> 00:00:56.640
you do a projection
onto two dimensions

00:00:56.640 --> 00:00:58.820
of a surface of a sphere,
the stuff at the bottom

00:00:58.820 --> 00:01:00.990
and the top look much bigger
than they actually are.

00:01:00.990 --> 00:01:03.200
Antarctica isn't
this big relative

00:01:03.200 --> 00:01:04.819
to say North America
or South America.

00:01:04.819 --> 00:01:06.040
It's just that we've
had to stretch it out

00:01:06.040 --> 00:01:07.090
to fill up the rectangle.

00:01:07.090 --> 00:01:09.469
But that's the Antarctic
Plate, North American Plate.

00:01:09.469 --> 00:01:11.010
And you can see that
they're actually

00:01:11.010 --> 00:01:12.680
moving relative to each other.

00:01:12.680 --> 00:01:16.010
And that's what these
arrows are depicting.

00:01:16.010 --> 00:01:19.020
You see right over
here the Nazca Plate

00:01:19.020 --> 00:01:21.680
and the Pacific Plate are
moving away from each other.

00:01:21.680 --> 00:01:23.079
New land is forming here.

00:01:23.079 --> 00:01:24.870
We'll talk more about
that in other videos.

00:01:24.870 --> 00:01:28.000
You see right over here in the
middle of the Atlantic Ocean

00:01:28.000 --> 00:01:31.434
the African Plate and the South
American Plate meet each other,

00:01:31.434 --> 00:01:33.350
and they're moving away
from each other, which

00:01:33.350 --> 00:01:37.590
means that new land, more plate
material I guess you could say,

00:01:37.590 --> 00:01:40.274
is somehow being
created right here--

00:01:40.274 --> 00:01:41.940
we'll talk about that
in future videos--

00:01:41.940 --> 00:01:46.690
and pushing these
two plates apart.

00:01:46.690 --> 00:01:50.050
Now, before we go into the
evidence for plate tectonics

00:01:50.050 --> 00:01:53.240
or even some of the more details
about how plates are created

00:01:53.240 --> 00:01:57.039
and some theories as to
why the plates might move,

00:01:57.039 --> 00:01:58.580
what I want to do
is get a little bit

00:01:58.580 --> 00:02:01.900
of the terminology of plate
tectonics out of the way.

00:02:01.900 --> 00:02:04.070
Because sometimes people
call them crustal plates,

00:02:04.070 --> 00:02:05.920
and that's not exactly right.

00:02:05.920 --> 00:02:08.360
And to show you the
difference, what I want to do

00:02:08.360 --> 00:02:11.600
is show you two different
ways of classifying

00:02:11.600 --> 00:02:13.025
the different
layers of the Earth

00:02:13.025 --> 00:02:15.400
and then think about how they
might relate to each other.

00:02:15.400 --> 00:02:17.400
So what you traditionally
see, and actually I've

00:02:17.400 --> 00:02:19.800
made a video that goes into
a lot more detail of this,

00:02:19.800 --> 00:02:24.350
is a breakdown of the
chemical layers of the Earth.

00:02:24.350 --> 00:02:26.050
And when I talk about
chemical layers,

00:02:26.050 --> 00:02:28.711
I'm talking about what
are the constituents

00:02:28.711 --> 00:02:29.710
of the different layers?

00:02:29.710 --> 00:02:31.460
So when you talk
of it in this term,

00:02:31.460 --> 00:02:35.000
the top most layer, which is the
thinnest layer, is the crust.

00:02:37.850 --> 00:02:39.710
Then below that is the mantle.

00:02:44.130 --> 00:02:46.150
Actually, let me show
you the whole Earth,

00:02:46.150 --> 00:02:48.360
although I'm not going
to draw it to scale.

00:02:48.360 --> 00:02:50.470
So if I were to draw
the crust, the crust

00:02:50.470 --> 00:02:54.200
is the thinnest outer
layer of the Earth.

00:02:54.200 --> 00:02:57.450
You can imagine the blue
line itself is the crust.

00:02:57.450 --> 00:03:00.300
Then below that,
you have the mantle.

00:03:00.300 --> 00:03:03.540
So everything between the
blue and the orange line,

00:03:03.540 --> 00:03:06.890
this over here is the mantle.

00:03:06.890 --> 00:03:08.980
So let me label the crust.

00:03:08.980 --> 00:03:12.320
The crust you can literally
view as the actual blue pixels

00:03:12.320 --> 00:03:13.310
over here.

00:03:13.310 --> 00:03:16.990
And then inside of the
mantle, you have the core.

00:03:16.990 --> 00:03:19.322
And when you do this
very high level division,

00:03:19.322 --> 00:03:20.530
these are chemical divisions.

00:03:20.530 --> 00:03:22.710
This is saying that
the crust is made up

00:03:22.710 --> 00:03:24.630
of different types of elements.

00:03:24.630 --> 00:03:26.560
Its makeup is different
than the stuff that's

00:03:26.560 --> 00:03:31.550
in the mantle, which is
made up of different things

00:03:31.550 --> 00:03:34.460
than what's inside the core.

00:03:34.460 --> 00:03:37.889
It's not describing the
mechanical properties of it.

00:03:37.889 --> 00:03:39.680
And when I talk about
mechanical properties

00:03:39.680 --> 00:03:52.870
I'm talking about whether
something is solid and rigid.

00:03:52.870 --> 00:03:57.150
Or maybe it's so hot and
melted it's kind of a magma,

00:03:57.150 --> 00:03:59.050
or kind of a plastic solid.

00:03:59.050 --> 00:04:02.940
So this would be the
most brittle stuff.

00:04:02.940 --> 00:04:06.260
If it gets warmed up, if rock
starts to melt a little bit,

00:04:06.260 --> 00:04:08.540
then you have
something like a magma,

00:04:08.540 --> 00:04:12.030
or you can view it as like a
deformable or a plastic solid.

00:04:12.030 --> 00:04:14.570
When we talk about plastic,
I'm not talking about the stuff

00:04:14.570 --> 00:04:18.279
that the case of your
cellphone is made of.

00:04:18.279 --> 00:04:20.230
I'm talking about
it's deformable.

00:04:20.230 --> 00:04:22.550
This rock is deformable
because it's so hot

00:04:22.550 --> 00:04:23.820
and it's somewhat melted.

00:04:23.820 --> 00:04:27.380
It kind of behaves like a fluid.

00:04:27.380 --> 00:04:28.980
It actually does
behave like a fluid,

00:04:28.980 --> 00:04:30.440
but it's much more viscous.

00:04:30.440 --> 00:04:31.999
It's much thicker
and slower moving

00:04:31.999 --> 00:04:33.540
than what we would
normally associate

00:04:33.540 --> 00:04:35.720
with a fluid like water.

00:04:35.720 --> 00:04:40.730
So this a viscous fluid.

00:04:40.730 --> 00:04:45.145
And then the most fluid would,
of course, be the liquid state.

00:04:45.145 --> 00:04:46.520
This is what we
mean when we talk

00:04:46.520 --> 00:04:48.320
about the mechanical properties.

00:04:48.320 --> 00:04:50.880
And when you look at
this division over here,

00:04:50.880 --> 00:04:54.570
the crust is solid.

00:04:54.570 --> 00:04:58.600
The mantle actually has some
parts of it that are solid.

00:04:58.600 --> 00:05:01.530
So the uppermost part
of the mantle is solid.

00:05:01.530 --> 00:05:05.140
Then below that, the
rest of the mantle

00:05:05.140 --> 00:05:10.240
is kind of in this magma,
this deformable, somewhat

00:05:10.240 --> 00:05:12.600
fluid state, and
depending on what depth

00:05:12.600 --> 00:05:14.160
you go into the
mantle there are kind

00:05:14.160 --> 00:05:15.780
of different levels of fluidity.

00:05:15.780 --> 00:05:18.000
And then the core,
the outer level layer

00:05:18.000 --> 00:05:20.450
of the core, the
outer core is liquid,

00:05:20.450 --> 00:05:22.040
because the
temperature is so high.

00:05:22.040 --> 00:05:24.660
The inner core is made
up of the same things,

00:05:24.660 --> 00:05:27.590
and the temperature
is even higher,

00:05:27.590 --> 00:05:30.010
but since the pressure is
so high it's actually solid.

00:05:30.010 --> 00:05:32.460
So that's why the mantle,
crust, and core differentiations

00:05:32.460 --> 00:05:36.810
don't tell you whether it's
solid, whether it's magma,

00:05:36.810 --> 00:05:38.380
or whether it's really a liquid.

00:05:38.380 --> 00:05:40.724
It just really tells
you what the makeup is.

00:05:40.724 --> 00:05:42.390
Now, to think about
the makeup, and this

00:05:42.390 --> 00:05:43.765
is important for
plate tectonics,

00:05:43.765 --> 00:05:45.426
because when we talk
about these plates

00:05:45.426 --> 00:05:47.050
we're not talking
about just the crust.

00:05:47.050 --> 00:05:50.500
We're talking about
the outer, rigid layer.

00:05:50.500 --> 00:05:53.430
Let me just zoom
in a little bit.

00:05:53.430 --> 00:05:57.420
Let's say we zoomed
in right over there.

00:05:57.420 --> 00:06:00.230
So now we have the
crust zoomed in.

00:06:00.230 --> 00:06:03.060
This right here is the crust.

00:06:03.060 --> 00:06:05.540
And then everything
below here we're actually

00:06:05.540 --> 00:06:08.344
talking about the upper mantle.

00:06:08.344 --> 00:06:10.510
We haven't gotten too deep
in the mantle right here.

00:06:10.510 --> 00:06:12.259
So that's why we call
it the upper mantle.

00:06:17.620 --> 00:06:19.530
Now, right below the
crust, the mantle

00:06:19.530 --> 00:06:24.030
is cool enough that it is
also in real solid form.

00:06:24.030 --> 00:06:30.370
So this right here
is solid mantle.

00:06:30.370 --> 00:06:31.930
And when we talk
about the plates

00:06:31.930 --> 00:06:34.640
were actually talking about
the outer solid layer.

00:06:34.640 --> 00:06:39.530
So that includes both the
crust and the solid part

00:06:39.530 --> 00:06:40.480
of the mantle.

00:06:40.480 --> 00:06:41.920
And we call that
the lithosphere.

00:06:46.060 --> 00:06:48.220
When people talk
about plate tectonics,

00:06:48.220 --> 00:06:49.970
they shouldn't say
crustal plates.

00:06:49.970 --> 00:06:52.635
They should call these
lithospheric plates.

00:06:57.720 --> 00:07:00.220
And then below the
lithosphere you

00:07:00.220 --> 00:07:02.540
have the least viscous
part of the mantle,

00:07:02.540 --> 00:07:07.580
because the temperature is high
enough for the rock to melt,

00:07:07.580 --> 00:07:11.970
but the pressure
isn't so large as what

00:07:11.970 --> 00:07:14.550
will happen when you go into
the lower part of the mantle

00:07:14.550 --> 00:07:18.070
that the fluid can actually
kind of move past each other,

00:07:18.070 --> 00:07:19.360
although still pretty viscous.

00:07:19.360 --> 00:07:20.340
This still a magma.

00:07:20.340 --> 00:07:23.930
So this is still kind
of in its magma state.

00:07:23.930 --> 00:07:26.530
And this fluid
part of the mantle,

00:07:26.530 --> 00:07:28.210
we can't quite call
it a liquid yet,

00:07:28.210 --> 00:07:32.420
but over large periods of time
it does have fluid properties.

00:07:32.420 --> 00:07:34.310
This, that essentially
the lithosphere

00:07:34.310 --> 00:07:37.120
is kind of riding on top of,
we call this the asthenosphere.

00:07:41.109 --> 00:07:43.400
So when we talk about the
lithosphere and asthenosphere

00:07:43.400 --> 00:07:45.340
we're really talking
about mechanical layers.

00:07:45.340 --> 00:07:48.140
The outer layer, the solid
layers, the lithosphere sphere.

00:07:48.140 --> 00:07:50.710
The more fluid layer right
below that is the asthenosphere.

00:07:50.710 --> 00:07:52.920
When we talk about the
crust, mantle, and core,

00:07:52.920 --> 00:07:55.310
we are talking about
chemical properties, what

00:07:55.310 --> 00:07:58.526
are the things
actually made up of.


Structure of the Earth

WEBVTT
Kind: captions
Language: en

00:00:00.374 --> 00:00:02.290
What I want to do in
this video is really make

00:00:02.290 --> 00:00:05.200
some clarifications and go
a little bit more in detail

00:00:05.200 --> 00:00:08.970
about the different
layers of the earth.

00:00:08.970 --> 00:00:12.590
So let me draw a cross-section
of the earth over here.

00:00:12.590 --> 00:00:13.767
And I'll try to do it.

00:00:13.767 --> 00:00:15.600
I won't be able to do
it perfectly to scale,

00:00:15.600 --> 00:00:18.190
but I'll try to do a little
bit better job at giving you

00:00:18.190 --> 00:00:21.740
a little bit of a sense of
how thick these layers are.

00:00:21.740 --> 00:00:24.390
So let's say that this
is the crust up here.

00:00:24.390 --> 00:00:26.300
And I'm going to make
the continental crust

00:00:26.300 --> 00:00:27.690
a little bit thicker.

00:00:27.690 --> 00:00:29.600
So let's say that that
is continental crust

00:00:29.600 --> 00:00:32.080
and this is continental crust.

00:00:32.080 --> 00:00:34.990
And then in between, let me
put some oceanic crust, which

00:00:34.990 --> 00:00:38.410
is going to be thinner.

00:00:38.410 --> 00:00:40.380
Actually, let me do that
in a different color.

00:00:40.380 --> 00:00:42.410
Let me do the oceanic
crust in blue.

00:00:42.410 --> 00:00:43.420
But this isn't water.

00:00:43.420 --> 00:00:44.235
This is rock.

00:00:44.235 --> 00:00:45.110
I'll do it in purple.

00:00:45.110 --> 00:00:46.146
That's even better.

00:00:46.146 --> 00:00:47.520
I don't want it
to be that thick.

00:00:47.520 --> 00:00:50.920
So let me draw the
oceanic crust-- is thinner

00:00:50.920 --> 00:00:52.340
than the continental
crust, which

00:00:52.340 --> 00:00:54.860
I'm trying to depict
right over here.

00:00:54.860 --> 00:01:01.540
So this right over
here is oceanic crust,

00:01:01.540 --> 00:01:04.185
and up here is
continental crust.

00:01:10.420 --> 00:01:13.450
And the thickness, or how
deep you can go and still

00:01:13.450 --> 00:01:16.170
be in crust, it depends
on where you are.

00:01:16.170 --> 00:01:19.830
And we know that near hot spots,
the oceanic crust can actually

00:01:19.830 --> 00:01:21.240
thin out a good bit.

00:01:21.240 --> 00:01:23.420
But roughly, when we
talk about the crust,

00:01:23.420 --> 00:01:24.920
we're talking about
something that's

00:01:24.920 --> 00:01:27.990
30 to 60 kilometers deep.

00:01:27.990 --> 00:01:31.740
So 30 to 60 kilometers deep.

00:01:31.740 --> 00:01:33.820
So if you are on
a continent, which

00:01:33.820 --> 00:01:36.540
I'm assuming you are, and
you dig for 20 kilometers,

00:01:36.540 --> 00:01:37.860
you will still be in the crust.

00:01:37.860 --> 00:01:40.020
30 kilometers, probably
still in the crust.

00:01:40.020 --> 00:01:43.630
If you dig for 70 kilometers
or 100 kilometers,

00:01:43.630 --> 00:01:46.482
you will probably
reach the mantle.

00:01:46.482 --> 00:01:48.190
And remember, what
we're describing here,

00:01:48.190 --> 00:01:51.054
when we talk about the crust,
the mantle, and the core,

00:01:51.054 --> 00:01:52.720
we're talking about
the chemical makeup.

00:01:52.720 --> 00:01:53.600
Let me make this clear.

00:01:53.600 --> 00:01:55.266
We're talking about
the chemical makeup.

00:01:57.750 --> 00:02:01.460
The crust is fundamentally
different than the mantle based

00:02:01.460 --> 00:02:04.430
on the molecules that
it is made up of,

00:02:04.430 --> 00:02:06.040
based on its composition.

00:02:06.040 --> 00:02:08.500
So let's talk about
the mantle now.

00:02:08.500 --> 00:02:11.120
So the mantle, layer like this.

00:02:11.120 --> 00:02:13.840
And once again, this is not
to scale because the crust,

00:02:13.840 --> 00:02:16.057
we're talking about
30 to 60 kilometers.

00:02:16.057 --> 00:02:17.890
The mantle, we're talking
about on the order

00:02:17.890 --> 00:02:21.650
about 2,900 or 3,000
kilometers thick.

00:02:21.650 --> 00:02:25.280
So this right here
is the entire mantle.

00:02:25.280 --> 00:02:26.780
So that's the mantle.

00:02:26.780 --> 00:02:34.980
And this is 2,900 to
3,000 kilometers thick.

00:02:34.980 --> 00:02:37.582
So this isn't even 1/30 of that.

00:02:37.582 --> 00:02:39.790
So I would have to draw it
even narrower than the way

00:02:39.790 --> 00:02:40.790
I've drawn it over here.

00:02:40.790 --> 00:02:43.220
And the mantle itself
can be subdivided

00:02:43.220 --> 00:02:46.250
into the upper mantle
and the lower mantle.

00:02:46.250 --> 00:02:50.010
So let me draw this
division right over here.

00:02:50.010 --> 00:02:52.020
The upper mantle, and
there's different ways

00:02:52.020 --> 00:02:54.240
to define the boundary.

00:02:54.240 --> 00:02:58.744
The upper mantle is roughly
about 700 kilometers down.

00:02:58.744 --> 00:02:59.910
So these are huge distances.

00:02:59.910 --> 00:03:02.030
I mean, this is
going straight down.

00:03:02.030 --> 00:03:04.300
So this is the upper mantle.

00:03:04.300 --> 00:03:07.860
Let me write it on the
actual mantle here.

00:03:07.860 --> 00:03:11.280
This is the upper mantle,
and this over here

00:03:11.280 --> 00:03:14.360
is the lower mantle.

00:03:14.360 --> 00:03:16.210
And just to be clear on things.

00:03:16.210 --> 00:03:18.530
So the crust is solid.

00:03:18.530 --> 00:03:21.240
Now when you go into
the upper mantle,

00:03:21.240 --> 00:03:23.412
the upper part of the
upper mantle-- and we'll

00:03:23.412 --> 00:03:24.870
talk about that a
little bit more--

00:03:24.870 --> 00:03:27.120
is cool enough to be solid.

00:03:27.120 --> 00:03:32.730
So there is a solid portion
of the upper mantle.

00:03:32.730 --> 00:03:36.080
So all of this up here is
solid because it's cool enough.

00:03:36.080 --> 00:03:41.310
It hasn't reached the melting
point of those rocks just yet.

00:03:41.310 --> 00:03:42.970
And we learned in
previous videos

00:03:42.970 --> 00:03:47.840
that the combination of the
solid part of the upper mantle

00:03:47.840 --> 00:03:50.576
and the crust combined, we
call that the lithosphere.

00:03:50.576 --> 00:03:52.200
And when we talk
about the lithosphere,

00:03:52.200 --> 00:03:54.116
we're not talking about
the mechanical makeup.

00:03:54.116 --> 00:03:56.870
We're not talking about what's
solid and what's not solid.

00:03:56.870 --> 00:03:57.995
So this is the lithosphere.

00:04:01.010 --> 00:04:02.520
You go a little bit deeper.

00:04:02.520 --> 00:04:05.440
Right below the lithosphere,
now the temperatures

00:04:05.440 --> 00:04:08.550
are high enough for-- and
I use the word liquid,

00:04:08.550 --> 00:04:09.800
but that's not exactly right.

00:04:09.800 --> 00:04:12.430
You can kind of think of it
as kind of a deformable solid,

00:04:12.430 --> 00:04:15.040
or a plastic solid or a magma.

00:04:15.040 --> 00:04:17.350
And that's the asthenosphere.

00:04:17.350 --> 00:04:22.280
So this area right over
here, this area right

00:04:22.280 --> 00:04:24.251
over here, the liquid
part-- actually, I

00:04:24.251 --> 00:04:25.500
shouldn't use the word liquid.

00:04:25.500 --> 00:04:26.590
Kind of deformable.

00:04:26.590 --> 00:04:29.040
It deforms over long
periods of time.

00:04:29.040 --> 00:04:32.630
But it is more fluid
than what we normally

00:04:32.630 --> 00:04:34.940
associate with rock
magma, would be a good way

00:04:34.940 --> 00:04:35.990
to think about it.

00:04:35.990 --> 00:04:38.080
That's what we call
the asthenosphere.

00:04:38.080 --> 00:04:41.146
It is fluid, just not
as fluid as water.

00:04:41.146 --> 00:04:43.020
It is more viscous than
something like water.

00:04:43.020 --> 00:04:44.228
So this is the asthenosphere.

00:04:47.870 --> 00:04:50.460
Now the upper mantle,
it's hot enough

00:04:50.460 --> 00:04:53.760
for the rock to
melt and be fluid.

00:04:53.760 --> 00:04:56.630
And the pressure is
low enough for it

00:04:56.630 --> 00:04:59.880
to still be able to kind
of move past itself,

00:04:59.880 --> 00:05:03.670
to still be somewhat fluid.

00:05:03.670 --> 00:05:08.804
But then once you get even
deeper, into the lower mantle,

00:05:08.804 --> 00:05:09.845
you have higher pressure.

00:05:13.390 --> 00:05:17.690
And so it's still fluid,
but it's less fluid.

00:05:17.690 --> 00:05:20.300
It's kind of thicker--
I guess, is the best

00:05:20.300 --> 00:05:23.800
way to think about it-- in the
lower mantle, it's thicker.

00:05:23.800 --> 00:05:26.230
So this whole area over
here, you could kind of

00:05:26.230 --> 00:05:27.930
think of it as melted rock.

00:05:27.930 --> 00:05:29.050
It's fluid.

00:05:29.050 --> 00:05:32.370
But the upper part of the
melted rock is more fluid.

00:05:32.370 --> 00:05:35.319
It's able to move easier,
because there's less pressure.

00:05:35.319 --> 00:05:37.860
And the pressure's just from
all of the rock that's above it.

00:05:37.860 --> 00:05:41.130
Remember, gravity is
pulling down on everything.

00:05:41.130 --> 00:05:44.550
Every molecule here wants to
go downward because of gravity.

00:05:44.550 --> 00:05:46.870
So it's applying
pressure downward.

00:05:46.870 --> 00:05:50.240
So the deeper you go, the
more pressure you get.

00:05:50.240 --> 00:05:53.620
Now, when we get even deeper
than that, we get to the core,

00:05:53.620 --> 00:05:55.770
and the core is divided
between the outer core

00:05:55.770 --> 00:05:57.480
and the inner core.

00:05:57.480 --> 00:06:04.260
So the outer core
and then, of course,

00:06:04.260 --> 00:06:05.350
you have the inner core.

00:06:10.230 --> 00:06:12.570
And just so we have a
sense for the distances,

00:06:12.570 --> 00:06:15.330
the width or the thickness
of the outer core

00:06:15.330 --> 00:06:18.351
is approximately
2,300 kilometers.

00:06:18.351 --> 00:06:20.850
So these are huge distances,
when you think about thickness.

00:06:20.850 --> 00:06:22.660
You could go down
another 2,300 kilometers,

00:06:22.660 --> 00:06:24.910
and you're in the-- or once
you go through the mantle,

00:06:24.910 --> 00:06:27.056
you can go 2,300 kilometers
to the outer core.

00:06:27.056 --> 00:06:28.430
And then you're
in the inner core

00:06:28.430 --> 00:06:29.690
and that essentially
takes you to the rest.

00:06:29.690 --> 00:06:31.481
That's essentially the
center of the earth.

00:06:31.481 --> 00:06:34.500
And the inner core--
Maybe I should

00:06:34.500 --> 00:06:36.620
draw the boundaries a
little bit more to scale.

00:06:36.620 --> 00:06:37.610
Let me do it this way.

00:06:37.610 --> 00:06:39.440
It should actually
look a little bit more

00:06:39.440 --> 00:06:45.290
like this, because
the outer core

00:06:45.290 --> 00:06:46.840
is thicker than the inner core.

00:06:46.840 --> 00:06:51.470
So the outer core is, as
I said, let me rewrite it.

00:06:51.470 --> 00:06:56.920
Outer core is on the order, it's
about 2,300 kilometers thick.

00:06:56.920 --> 00:07:00.060
And then you have
your inner core.

00:07:00.060 --> 00:07:01.160
I shouldn't do it in blue.

00:07:01.160 --> 00:07:03.720
I should do it in a hot color.

00:07:03.720 --> 00:07:05.709
So the inner core
right over here

00:07:05.709 --> 00:07:07.750
just kind of takes us to
the center of the earth.

00:07:07.750 --> 00:07:11.620
And that's a little over
1,000 kilometers thick.

00:07:11.620 --> 00:07:14.510
So this is the inner core.

00:07:14.510 --> 00:07:18.590
The number I have is about
1,200 kilometers thick.

00:07:18.590 --> 00:07:21.900
And both the-- the entire
core, both the outer core

00:07:21.900 --> 00:07:23.817
and the inner core, is
mainly nickel and iron.

00:07:23.817 --> 00:07:25.441
Think about when the
earth was forming.

00:07:25.441 --> 00:07:27.810
What happens is when this
whole earth was super hot

00:07:27.810 --> 00:07:29.730
and was kind of
in a fluid state,

00:07:29.730 --> 00:07:31.230
the heavier elements
were allowed

00:07:31.230 --> 00:07:35.182
to sink down, when
everything was fluid.

00:07:35.182 --> 00:07:37.140
The things that were in
between would kind of--

00:07:37.140 --> 00:07:38.850
or the things that were
lighter would go up.

00:07:38.850 --> 00:07:40.560
And then the gases, things
that would naturally

00:07:40.560 --> 00:07:42.280
be in the gaseous
state, would kind of

00:07:42.280 --> 00:07:47.400
bubble up through that
fluid, kind of the way,

00:07:47.400 --> 00:07:50.287
actually, carbon
bubbles up in a soda,

00:07:50.287 --> 00:07:52.120
it would eventually
bubble out of the fluid,

00:07:52.120 --> 00:07:54.049
and it would actually
form the atmosphere.

00:07:54.049 --> 00:07:56.590
So that's why, when you look at
the composition of the earth,

00:07:56.590 --> 00:07:58.510
you have the densest,
the heaviest elements,

00:07:58.510 --> 00:07:59.460
at the center.

00:07:59.460 --> 00:08:02.640
And then the lightest elements
are forming the atmosphere.

00:08:02.640 --> 00:08:04.570
And the outer core and
the inner core, they

00:08:04.570 --> 00:08:07.225
are made up predominantly
of nickel and iron.

00:08:11.350 --> 00:08:13.250
And their makeup is
actually very similar.

00:08:13.250 --> 00:08:15.790
So this division--
Chemically, they

00:08:15.790 --> 00:08:17.980
have a very similar composition.

00:08:17.980 --> 00:08:21.020
What's different about
them is at the outer core,

00:08:21.020 --> 00:08:22.650
you have temperatures
high enough

00:08:22.650 --> 00:08:24.360
that nickel and iron can melt.

00:08:24.360 --> 00:08:26.860
But the pressures are low
enough that they can still

00:08:26.860 --> 00:08:28.610
be in a fluid state.

00:08:28.610 --> 00:08:33.169
So this is our
liquid outer core.

00:08:33.169 --> 00:08:36.000
And this has a
pretty low viscosity,

00:08:36.000 --> 00:08:38.220
especially even
relative to the mantle.

00:08:38.220 --> 00:08:39.900
So that's why people
kind of consider

00:08:39.900 --> 00:08:42.309
this in kind of a more
traditional liquid state.

00:08:42.309 --> 00:08:44.360
But as you get deeper
and deeper and deeper,

00:08:44.360 --> 00:08:47.280
the pressure becomes
so huge as you

00:08:47.280 --> 00:08:50.720
get to the inner core-- remember
all of the weight of all

00:08:50.720 --> 00:08:53.610
of the rock above you, of these
thousands of miles of rock

00:08:53.610 --> 00:08:56.740
above you, is all pushing
down on the rock below it.

00:08:56.740 --> 00:08:59.140
So the inner core, even though
the temperature is really,

00:08:59.140 --> 00:09:02.020
really, really hot,
the pressure is so big

00:09:02.020 --> 00:09:04.550
that the molecules can't
flow past each other.

00:09:04.550 --> 00:09:05.840
They can't be liquid.

00:09:05.840 --> 00:09:07.640
They're kind of jam-packed.

00:09:07.640 --> 00:09:09.970
And so the inner core,
because of the high pressure,

00:09:09.970 --> 00:09:13.490
despite the high
temperature, is solid.

00:09:13.490 --> 00:09:14.104
It's solid.

00:09:14.104 --> 00:09:15.520
So the difference
here is actually

00:09:15.520 --> 00:09:18.429
a mechanical one between the
outer core and the inner core.

00:09:18.429 --> 00:09:20.220
They're made up of the
same things, roughly

00:09:20.220 --> 00:09:21.290
the same chemical makeup.

00:09:21.290 --> 00:09:24.330
It's just slightly-- or
lower pressure on the outside

00:09:24.330 --> 00:09:26.432
so you can actually
be in a fluid state.

00:09:26.432 --> 00:09:28.140
So hopefully that
clarifies and gives you

00:09:28.140 --> 00:09:32.630
a little bit of depth on
the makeup of the earth.


Plate tectonics: Geological features of divergent plate boundaries

WEBVTT
Kind: captions
Language: en

00:00:00.570 --> 00:00:02.480
Before we go into
possible theories

00:00:02.480 --> 00:00:05.920
as to why plates actually move,
what I want to do in this video

00:00:05.920 --> 00:00:09.610
is think a little bit about why
we see the geological features

00:00:09.610 --> 00:00:11.760
we do see at plate boundaries.

00:00:11.760 --> 00:00:15.020
And in particular, I want
to focus on the features

00:00:15.020 --> 00:00:17.040
we see at divergent
plate boundaries,

00:00:17.040 --> 00:00:19.120
where the plates are moving
away from each other,

00:00:19.120 --> 00:00:20.910
or where new land
is being created

00:00:20.910 --> 00:00:25.400
like we saw in the mid-oceanic
ridges, where we see

00:00:25.400 --> 00:00:27.730
new land being created
right in the center

00:00:27.730 --> 00:00:29.780
and moving outwards from them.

00:00:29.780 --> 00:00:34.220
So to do that, let's think
about the different layers.

00:00:34.220 --> 00:00:36.290
And actually I want to
make one quick correction

00:00:36.290 --> 00:00:37.430
on the last video.

00:00:37.430 --> 00:00:40.160
Over here I had drawn these
arrows going in that direction.

00:00:40.160 --> 00:00:41.700
And based on how I
defined them they

00:00:41.700 --> 00:00:42.990
should have been
going into the page.

00:00:42.990 --> 00:00:44.920
And so they should have
had these X's there.

00:00:44.920 --> 00:00:46.420
Now, with that out
of the way, let's

00:00:46.420 --> 00:00:49.160
draw a little diagram
of what happens

00:00:49.160 --> 00:00:53.130
in the early stages of these
divergent plate boundaries.

00:00:53.130 --> 00:00:59.070
So you might have
your just your crust,

00:00:59.070 --> 00:01:01.340
and maybe it's
continental crust.

00:01:01.340 --> 00:01:05.480
So this right here
is the Earth's crust.

00:01:05.480 --> 00:01:08.842
And then you have the
solid part of the mantle,

00:01:08.842 --> 00:01:10.800
and the combination of
them is the lithosphere.

00:01:15.740 --> 00:01:17.460
And then you have
the liquid part,

00:01:17.460 --> 00:01:20.420
or the super hot
part of the mantle.

00:01:20.420 --> 00:01:22.755
So this down here is magma.

00:01:22.755 --> 00:01:23.630
It hasn't solidified.

00:01:23.630 --> 00:01:25.560
It's hot enough to be
in the liquid state.

00:01:25.560 --> 00:01:28.520
And all of this combined,
so this right here we

00:01:28.520 --> 00:01:29.375
consider the mantle.

00:01:32.180 --> 00:01:33.860
Now, there's some
debate, and we'll

00:01:33.860 --> 00:01:35.276
talk about this
in the next video,

00:01:35.276 --> 00:01:37.350
of how hot spots actually form.

00:01:37.350 --> 00:01:39.780
It could be these
mantle plumes that

00:01:39.780 --> 00:01:43.580
start at the border between
the mantle and the core.

00:01:43.580 --> 00:01:45.440
It could be some type
of convection currents

00:01:45.440 --> 00:01:46.456
in the actual mantle.

00:01:46.456 --> 00:01:48.330
We'll talk more about
that in the next video,

00:01:48.330 --> 00:01:50.750
or maybe a few videos from now.

00:01:50.750 --> 00:01:53.500
But let's take it for
granted that hot spots form

00:01:53.500 --> 00:01:54.860
in the mantle.

00:01:54.860 --> 00:01:58.030
So let's say we have an
area of magma right here

00:01:58.030 --> 00:01:59.540
that is particularly hot.

00:01:59.540 --> 00:02:01.660
Let me do this in another color.

00:02:01.660 --> 00:02:03.680
I'll do it in pink.

00:02:03.680 --> 00:02:07.130
So this is particularly
hot magma here.

00:02:07.130 --> 00:02:08.792
And we know, or
maybe we don't know,

00:02:08.792 --> 00:02:11.250
well, you'll learn right now,
if you take the same material

00:02:11.250 --> 00:02:12.730
and you make it
hotter it's going

00:02:12.730 --> 00:02:16.270
to become less dense, because
the particles essentially

00:02:16.270 --> 00:02:18.720
are going to bump into each
other with more kinetic energy

00:02:18.720 --> 00:02:21.230
and have more space
in between them.

00:02:21.230 --> 00:02:23.860
And so this really
hot part of the magma,

00:02:23.860 --> 00:02:25.960
or this really hot
part of the mantle, it

00:02:25.960 --> 00:02:30.650
is going to move upwards,
because it is less dense.

00:02:30.650 --> 00:02:32.310
It will have buoyancy.

00:02:32.310 --> 00:02:35.160
And as it moves upwards, it will
heat up the things around it.

00:02:35.160 --> 00:02:37.750
And it will eventually make
its way into the lithosphere.

00:02:37.750 --> 00:02:40.260
And it'll kind of be able to
break through the lithosphere

00:02:40.260 --> 00:02:43.510
because it's so hot it can
kind of melt its way through.

00:02:43.510 --> 00:02:45.240
So let's fast forward this.

00:02:45.240 --> 00:02:47.220
Let's fast forward
this a little bit.

00:02:47.220 --> 00:02:49.150
So this is step one up here.

00:02:49.150 --> 00:02:50.620
Now step two.

00:02:50.620 --> 00:02:54.975
This hot magma is rising
now through the lithosphere,

00:02:54.975 --> 00:02:56.600
and so it's going to
create a hot spot.

00:02:56.600 --> 00:02:58.600
It's going to create a
dome in the lithosphere

00:02:58.600 --> 00:03:00.210
and actually on the crust.

00:03:00.210 --> 00:03:02.270
And so it might look like this.

00:03:02.270 --> 00:03:05.950
So the crust is now going
to have a dome in it.

00:03:05.950 --> 00:03:10.270
And this was the
original lithosphere.

00:03:10.270 --> 00:03:14.000
And it's now kind of been
broken in two by this hot spot.

00:03:14.000 --> 00:03:18.690
So the lithosphere
is now broken in two,

00:03:18.690 --> 00:03:21.060
or it's about to be broken
in two by this hot spot.

00:03:21.060 --> 00:03:23.490
So all of this is
still the lithosphere.

00:03:23.490 --> 00:03:25.420
I'll just write litho for short.

00:03:25.420 --> 00:03:28.050
This up here is the crust.

00:03:28.050 --> 00:03:30.355
And if you take any rigid
material, and the crust

00:03:30.355 --> 00:03:32.480
and the lithosphere for
that matter, they're rigid,

00:03:32.480 --> 00:03:34.950
and you push outward on
it, it won't stretch nicely

00:03:34.950 --> 00:03:36.550
like a nice elastic balloon.

00:03:36.550 --> 00:03:39.280
It'll start to crack and have
to be pulled apart in order

00:03:39.280 --> 00:03:42.370
to kind of take the
pushing from below.

00:03:42.370 --> 00:03:45.909
So this crust is going
to start to crack.

00:03:45.909 --> 00:03:47.950
And actually, the best
example where you see this

00:03:47.950 --> 00:03:49.710
is actually in like
sourdough bread

00:03:49.710 --> 00:03:51.600
that has really hard
shells around it.

00:03:51.600 --> 00:03:52.760
You see sourdough bread.

00:03:52.760 --> 00:03:55.840
Let me see if I can draw
a roll of sourdough bread.

00:03:55.840 --> 00:03:58.870
It has all of these
cracks in the surface.

00:03:58.870 --> 00:04:01.120
And that's because the
outer layer, the outer shell

00:04:01.120 --> 00:04:02.830
of the bread, is really rigid.

00:04:02.830 --> 00:04:06.410
And so the inside heats up and
the surface area has to expand.

00:04:06.410 --> 00:04:10.190
These kind of rifts
form in the bread

00:04:10.190 --> 00:04:14.700
to allow that kind of rigid
shell to actually expand.

00:04:14.700 --> 00:04:16.940
And that exact same
thing would happen

00:04:16.940 --> 00:04:19.790
to the crust, or actually
the entire lithosphere.

00:04:19.790 --> 00:04:24.315
So let me draw this
hot spot again.

00:04:24.315 --> 00:04:26.810
Let me do it in that pink color.

00:04:26.810 --> 00:04:30.450
Now the hot spot
has gotten this far.

00:04:30.450 --> 00:04:33.930
This is the hot magma
right over here.

00:04:33.930 --> 00:04:38.377
And if we fast forward
even a little bit more,

00:04:38.377 --> 00:04:39.960
then you could
actually have the crust

00:04:39.960 --> 00:04:42.340
starting to be
fully pulled apart.

00:04:42.340 --> 00:04:44.760
So you fast forward
a little bit more,

00:04:44.760 --> 00:04:46.560
the bottom boundary
of the lithosphere

00:04:46.560 --> 00:04:49.270
maybe now starts to look
something like this.

00:04:49.270 --> 00:04:54.160
The magma has kind of broken
through the hardened part,

00:04:54.160 --> 00:04:55.860
the rigid part of the mantle.

00:04:55.860 --> 00:04:59.640
So maybe it looks
like this right now.

00:04:59.640 --> 00:05:04.080
You have your hot
spot right over here.

00:05:04.080 --> 00:05:07.630
It's gotten that far now.

00:05:07.630 --> 00:05:12.650
And the crust on top, the actual
what we would kind of normally

00:05:12.650 --> 00:05:15.370
see has now been pulled
apart to kind of have

00:05:15.370 --> 00:05:16.960
to cover this new surface area.

00:05:16.960 --> 00:05:19.570
So now it kind of looks
something like this.

00:05:19.570 --> 00:05:21.420
So it's been pushed apart.

00:05:21.420 --> 00:05:23.636
Let me see how well
I can draw this.

00:05:23.636 --> 00:05:25.510
So now it's been pushed
apart, and as it gets

00:05:25.510 --> 00:05:27.434
pushed apart it kind of
thins out a little bit

00:05:27.434 --> 00:05:28.600
as you can imagine it doing.

00:05:28.600 --> 00:05:31.110
It's almost exactly
as the bread analogy.

00:05:31.110 --> 00:05:34.980
When you look at bread like
this the rift, the depressions

00:05:34.980 --> 00:05:37.380
where it was expanding
most vigorously,

00:05:37.380 --> 00:05:39.440
those parts of the bread
are actually thinner,

00:05:39.440 --> 00:05:41.565
like these parts of the
bread are actually thinner,

00:05:41.565 --> 00:05:44.190
and they're not as hard as
the parts that moved away.

00:05:44.190 --> 00:05:46.800
And you see that exact same
thing happening with the land.

00:05:49.960 --> 00:05:55.020
And all of this
stuff is continuously

00:05:55.020 --> 00:05:56.550
getting pushed
outward, essentially

00:05:56.550 --> 00:05:58.280
to kind of make space
for this hot spot.

00:05:58.280 --> 00:06:00.380
Now, this step
right over here, you

00:06:00.380 --> 00:06:03.120
might have a volcano or
two, but more important,

00:06:03.120 --> 00:06:05.780
you're going to have what's
called a rift valley.

00:06:05.780 --> 00:06:08.480
Right now we're assuming that
we're not below sea level yet,

00:06:08.480 --> 00:06:11.010
or we're assuming that
this kind of depression

00:06:11.010 --> 00:06:13.030
in the land that
you see here hasn't

00:06:13.030 --> 00:06:15.210
come in contact with
another body of water.

00:06:15.210 --> 00:06:17.310
And so it'll just kind
of become a little valley

00:06:17.310 --> 00:06:18.950
in between higher land.

00:06:18.950 --> 00:06:21.930
And you actually
see that on Earth.

00:06:21.930 --> 00:06:25.710
And the most famous is
the African Rift Valley.

00:06:25.710 --> 00:06:28.126
That's right about
this region here.

00:06:28.126 --> 00:06:29.500
Actually, I have
a better diagram

00:06:29.500 --> 00:06:32.990
that depicts the African
Rift Valley right over here.

00:06:32.990 --> 00:06:35.060
It's this whole region
of Africa is actually

00:06:35.060 --> 00:06:41.770
kind of a big valley created
by a hot spot right over there.

00:06:41.770 --> 00:06:46.720
Now, as the hot spot kind
of keeps maturing eventually

00:06:46.720 --> 00:06:52.420
some of the rift will
become so depressed

00:06:52.420 --> 00:06:54.220
that it will actually
be below sea level.

00:06:54.220 --> 00:06:58.200
Remember, all this land up
here is being stretched apart.

00:06:58.200 --> 00:06:59.680
So let me go to the next step.

00:06:59.680 --> 00:07:01.840
The next step will
be right over here.

00:07:01.840 --> 00:07:05.980
The land on top is now
maybe below sea level

00:07:05.980 --> 00:07:07.730
in this next step, and
it comes in contact

00:07:07.730 --> 00:07:09.910
with maybe an ocean or a sea.

00:07:09.910 --> 00:07:12.260
And so now it might
look like this.

00:07:12.260 --> 00:07:15.980
So now the land is
super thin on top.

00:07:15.980 --> 00:07:17.820
I'll do my best to draw it.

00:07:17.820 --> 00:07:19.580
So it's super thin
on top, and remember

00:07:19.580 --> 00:07:26.790
it kind of keeps
getting pulled apart

00:07:26.790 --> 00:07:31.290
from this bubble of hot magma
that's essentially coming up

00:07:31.290 --> 00:07:32.980
from below.

00:07:32.980 --> 00:07:35.970
Let me draw it like this.

00:07:35.970 --> 00:07:37.880
This is all solid rock here.

00:07:37.880 --> 00:07:39.680
What I drew in
orange is the crust.

00:07:39.680 --> 00:07:46.320
This is kind of the
rocky part of the mantle.

00:07:46.320 --> 00:07:48.350
So the combination
is the lithosphere.

00:07:48.350 --> 00:07:52.747
And now you have the hot
magma coming up like this.

00:07:52.747 --> 00:07:54.580
And it might peek through
every now and then

00:07:54.580 --> 00:07:55.780
and create a volcano there.

00:07:55.780 --> 00:07:57.946
Maybe it'll peak through
and create a volcano there.

00:07:57.946 --> 00:08:01.570
But in general, it's going
to keep pushing the land up

00:08:01.570 --> 00:08:02.231
and outwards.

00:08:02.231 --> 00:08:04.230
And so this land, even
though you're saying hey,

00:08:04.230 --> 00:08:06.910
it's being pushed up, because
of the outward motion,

00:08:06.910 --> 00:08:08.580
this land over here
is going to be lower

00:08:08.580 --> 00:08:10.910
than the land around it,
like the loaf of bread.

00:08:10.910 --> 00:08:13.400
If it gets low enough
and comes in below sea

00:08:13.400 --> 00:08:16.579
level actually and comes in
contact with a body of water,

00:08:16.579 --> 00:08:18.120
or even if it doesn't
actually, water

00:08:18.120 --> 00:08:19.910
will start to gather over there.

00:08:23.220 --> 00:08:26.540
And once again, we
actually see that

00:08:26.540 --> 00:08:31.070
in the rift forming between
the African and Arabian plates.

00:08:31.070 --> 00:08:34.809
The Red Sea is actually an
example of exactly that.

00:08:34.809 --> 00:08:38.530
The Arabian Plate is moving
away from the African

00:08:38.530 --> 00:08:41.280
Plate because of this hot spot.

00:08:41.280 --> 00:08:44.759
This is pushing all of the land
up and out right over here.

00:08:44.759 --> 00:08:45.800
And so this is going out.

00:08:45.800 --> 00:08:47.030
That is going out.

00:08:47.030 --> 00:08:49.172
It's moving outward
in every direction.

00:08:49.172 --> 00:08:50.630
And so it creates
these depressions

00:08:50.630 --> 00:08:51.860
where water can flow inwards.

00:08:51.860 --> 00:08:55.570
The Rift Valley hasn't had
water flow into it the way

00:08:55.570 --> 00:08:58.676
the Red Sea has just yet, but
if it kept happening eventually

00:08:58.676 --> 00:09:00.800
it's going to get low enough
so that the water will

00:09:00.800 --> 00:09:01.460
flow into it.

00:09:01.460 --> 00:09:03.269
So the Red Sea is exactly that.

00:09:03.269 --> 00:09:04.810
You essentially have
the Indian Ocean

00:09:04.810 --> 00:09:09.060
flowing into this rift that
formed from this hot spot.

00:09:09.060 --> 00:09:12.020
And then if you fast forward
a bunch so that finally

00:09:12.020 --> 00:09:14.360
the magma can kind of surface.

00:09:14.360 --> 00:09:17.450
So let's fast forward from
even this point even more.

00:09:17.450 --> 00:09:20.370
So let's fast forward
even more, and let's say

00:09:20.370 --> 00:09:23.300
now the land has been
pushed a good bit apart.

00:09:23.300 --> 00:09:25.720
Now the hot spot has
actually surfaced.

00:09:25.720 --> 00:09:27.740
Now the crust might look
something like this.

00:09:31.630 --> 00:09:34.750
So it's been pushed apart
a good bit at this point.

00:09:34.750 --> 00:09:38.480
Now we're talking about on the
order of hundreds of thousands

00:09:38.480 --> 00:09:40.270
of years or tens of
thousands of years.

00:09:40.270 --> 00:09:42.920
So the land, for example,
the land that was here,

00:09:42.920 --> 00:09:45.850
this part of the land
might now be out here.

00:09:45.850 --> 00:09:49.890
And this part of the land
might now be out here.

00:09:49.890 --> 00:09:53.020
What's going to happen
is that this hot spot

00:09:53.020 --> 00:09:54.700
is going to continue
to fuel, and we're

00:09:54.700 --> 00:09:56.940
assuming everything's
underwater at this point.

00:09:56.940 --> 00:09:59.790
Since this depression that
was created is now so low

00:09:59.790 --> 00:10:02.380
the crust was stretched thin.

00:10:02.380 --> 00:10:05.076
We're going to assume that
all of this is underwater.

00:10:05.076 --> 00:10:06.450
The hot spot is
essentially going

00:10:06.450 --> 00:10:13.600
to come out of
underwater volcanoes

00:10:13.600 --> 00:10:18.560
and start creating what's now--
this body of water's gotten

00:10:18.560 --> 00:10:21.410
large enough that we can
call it a mid-oceanic ridge.

00:10:21.410 --> 00:10:29.180
And so it'll actually start
creating an actual ridge

00:10:29.180 --> 00:10:31.060
with volcanoes in the center.

00:10:31.060 --> 00:10:39.770
So that's why one, we see things
like the Rift Valley in Africa,

00:10:39.770 --> 00:10:41.565
we see things like the Red Sea.

00:10:41.565 --> 00:10:43.190
And maybe even more
importantly, that's

00:10:43.190 --> 00:10:46.590
why we see something like the
mid-Atlantic rift in the middle

00:10:46.590 --> 00:10:49.110
of the Atlantic
Ocean, where you have

00:10:49.110 --> 00:10:51.390
all of this depressed
land that was essentially

00:10:51.390 --> 00:10:54.620
analogous to that Rift Valley
but it's at a much later stage.

00:10:54.620 --> 00:10:56.550
And that's why it's
able to collect water,

00:10:56.550 --> 00:10:58.210
because when the
land was pushed out

00:10:58.210 --> 00:11:01.630
and stretched thin water was
able to flow into it, going

00:11:01.630 --> 00:11:04.360
back to the bread
analogy, essentially

00:11:04.360 --> 00:11:08.200
when this bread was baking
and this part of the crust

00:11:08.200 --> 00:11:10.704
pushed outwards, you
had this rift form,

00:11:10.704 --> 00:11:12.620
and then if there was
some water on the bread,

00:11:12.620 --> 00:11:13.650
or if it was raining,
or if it was connected

00:11:13.650 --> 00:11:15.066
to a body of water,
water would've

00:11:15.066 --> 00:11:17.230
eventually flowed in here.

00:11:17.230 --> 00:11:19.160
And if that bread
kept growing this rift

00:11:19.160 --> 00:11:20.618
would have kept
growing, eventually

00:11:20.618 --> 00:11:24.710
to the size of the Atlantic
Ocean in our theoretical bread.

00:11:24.710 --> 00:11:27.550
And so that's why you have
this huge depressed area where

00:11:27.550 --> 00:11:29.380
the ocean can form,
but in the middle of it

00:11:29.380 --> 00:11:32.180
you kind of have this you
have this submersed you

00:11:32.180 --> 00:11:34.230
have this actual
submersed mountain

00:11:34.230 --> 00:11:36.880
chain, this submersed
chain of volcanoes,

00:11:36.880 --> 00:11:40.030
this submersed ridge where
the land actually does go up

00:11:40.030 --> 00:11:42.851
a little bit because of all
that magma flowing directly

00:11:42.851 --> 00:11:43.350
out of it.

00:11:43.350 --> 00:11:45.058
So hopefully that
clears up a little bit.

00:11:45.058 --> 00:11:47.550
That was always confusing to
me why you see uplifted land

00:11:47.550 --> 00:11:51.160
but then everything around the
uplifted land is much lower,

00:11:51.160 --> 00:11:54.280
and why the whole thing is
submersed as it's moving away.

00:11:54.280 --> 00:11:57.690
So hopefully that clears
things up a little bit.