Lesson video

Hello, my name's Mrs. Harking and today we're going to be exploring inside Earth.

This lesson is taken from the unit, "Tectonic Hazards: Why is Earth restless?" This is actually a topic humans don't know huge amounts about.

Humans know more about the surface of the moon than they do about the inside of our planet Earth.

By the end of the lesson today, we will be able to describe the structure of the Earth and how the pattern of earthquakes and volcanoes relate to the Earth's tectonic plates.

Here's some keywords that will be useful to know before we start the lesson today.

If you feel like you'd like to write any of these down, please feel free to pause the video.

Pressure is a force pushing or pressing on a given area.

Dense means the mass of something compared to its volume, so if something is very dense, that's means that actually there is a lot of mass, a lot of stuff in it compared to its size.

Tectonic plates is the huge pieces that Earth's lithosphere are broken into and plate boundary, these are the points where two tectonic plates meet.

Today's lesson will be in two parts.

First, we'll look at the structure of Earth and then we'll move on to tectonic plates.

So first of all, the structure of Earth.

As I said, we know very little about the centre of our planet.

Just to give you an idea of this for scale, the highest points on Earth is Mount Everest, and this is 8.

9 kilometres high.

The deepest active mine is 3.

9 kilometres deep.

Now the deepest natural point on Earth is the Mariana Trench and this is 10.

9 kilometres deep.

That's pretty deep.

The deepest point now, is actually a human feature.

It is the Kola borehole, which is 12.

3 kilometres deep.

The Kola borehole in Russia is the deepest hole ever drilled by humans, but this only scratches the surface, because the centre of the Earth is over 6,000 kilometres deep, so we've only got 12.

3 kilometres into our planet.

There's a lot of kilometres left to go before we get to the centre.

How do we know what it is like deep underground if no human has been deep at all? How do we know? Well, actually, scientists make predictions using the information such as earthquake detection and you can see this animation here shows an earthquake and the vibrations rippling through the planet and although the earthquake won't be felt by humans, at least, across the whole planet, we have got detectors that will detect these earthquakes and they will be able to feel very slight vibrations around the planet.

So by comparing how these seismic waves or vibrations are felt around the world, it allows scientists to predict the properties of different layers of our planets.

So some seismic waves are not transmitted through liquids, so that can tell us whether different parts of our planet are liquid or solid, for example and Earth has four main layers.

We've got the crust, the mantle, the outer core and the inner core.

Now, I always think about these layers like the crust is on the outside, like the crust of the bread is on the outside of a loaf of bread and then the core, the core of an apple is in the middle of the apple just in the same way that the core of our planet is in the middle.

Obviously, a loaf of bread is not a perfect sphere and again, an apple core goes the whole way through from top to bottom with the apple, as opposed to here where the core is just a ball in the centre, but it's something to help you remember.

Each layer has distinct chemical characteristics.

That's how we have separated each section.

So the chemistry, what it is made from makes the crust different from the mantle and the mantle different from the outer core and inner core, et cetera.

Right, let's see if you can remember.

What are the four layers of the Earth? Is it A? The inner core, outer core, mantle and crust.

Is it B? The lithosphere, atmosphere, outer core and crust.

Or is it C? The mantle, crust, hydrosphere and core.

Well done.

Yes, it's a the inner core, outer core, mantle and crust.

Here on our diagram of the structure of the Earth, we can see the core.

It's made up of iron and nickel and the core has two parts.

So the inner core is solid and the outer core is liquid.

The inner core has radioactive processes going on which generate heat.

The temperature of the inner core is estimated to be 5,500 degrees C.

Notice I say estimated.

Nobody has been there and put a thermometer there and that is comparable to the surface of the sun that is seriously hot.

Despite this high temperature, the Earth's inner core is solid, so it hasn't melted into a liquid, as you might imagine, by extreme heat and the reason for that is because of the intense pressure caused by the layers above it.

There's a huge amount of rocks squeezing down on top of it and that is squashing it into a solid form.

It's making it very, very dense.

We can see here on this diagram that the centre of the Earth is the hottest space.

We've just said that's 5,500 degrees, we think, didn't we? But as you move towards the surface, where we are, the temperature reduces.

So the temperature of the rock reduces with distance from the inner core.

The outer core is a liquid.

As it is so hot, the rock has melted.

So yes, it is a bit cooler than the inner core, but it's still really hot, so hot that rock can melt.

So unlike the inner core, there's not quite enough pressure above it, so there's not quite enough rock surrounding it and squashing it to create a solid.

So it hasn't been forced into that really, really dense form, which will force even super, super hot rock to become a solid.

So this layer, the outer core is liquid, hot enough to be melted into a liquid, not enough pressure to force it into a solid.

Time for a quick check for understanding.

Which diagram shows the highest temperature rock marked with an X? Is it A, B, or C? Well done, yes, it's B.

So right in the centre of our planet, in the inner core, that is where it is hottest.

Time for another quick check.

Name the layer that is liquid.

Yes, it's the outer core, not the inner core.

That's solid.

The outer core is liquid.

How do we know this? Well done, we know this because some seismic waves are not transmitted through liquids.

The mantle is our next layer.

It is the thickest layer at 2,900 kilometres.

The mantle has a high proportion of iron, calcium and magnesium.

The mantle is mostly solid, but roughly 1% of the mantle is thought to flow like a very thick fluid.

So this movement occurs over thousands to millions of years, so extremely slowly.

There is a misconception out there, a lot of students misunderstand this and they think that actually the mantle is a bit like jam or honey and it's flowing quite quickly all the time.

That's not the case at all.

The mantle is actually mostly solid, so only 1% is actually thoughts of flow, and that is really, really slowly.

Quick check for understanding now.

True or false? The mantle rocks are melted into a liquid and they circulate fast.

Well done, it's false.

Can you tell me why it's false? Good, so the mantle is mostly solid, but only 1% roughly of the mantle is thought to flow like a very thick fluid.

So this movement occurs over thousands to millions of years.

So it's not a liquid that circulates fast at all.

Only naught to 65 kilometres thick.

The crust is the thinnest and the coolest layer.

It's made up of 93 elements.

So the closer to the surface you are, the more elements are involved in each of these layers.

This is where our continents and oceans are and it is the layer on which we live.

The crest is thickest where there is land and thinnest under the oceans.

Quick check for understanding, which is the layer of the Earth that we live on.

Well done, it's the crust.

Right, time for a task now.

So I would like you to label the names of the layers of the Earth and add one of the following details to each layer.

So I would like the name for each layer on there and then as well as that name.

Could you look at the bullet points I've got here on the right hand side? So liquids, highest temperature, coolest temperature, thickest layer.

I would like you to attach those as well to each of those labels.

So what features do each of these layers have? Next, I would like you to correct this statement.

So there are mistakes here.

You need to work out how many there are, what they are and correct them.

The mantle is mostly liquid, roughly 99% of the mantle is thought to flow like a very thick fluid.

This movement occurs over one to two years.

So what's wrong with that? I'm sure you can spot some things already.

Right, feel free to pause video now and I'll check back in with you in a moment to see how you got on.

Well done everyone, good effort.

So your work may look like this.

We can see here the labels added onto our planet.

We've got the crust on the outside with the coolest temperatures.

Next layer down is our mantle, which is the thickest layer.

Then the outer core, which is liquids and then the inner core, which has the highest temperature.

The corrected statement should read like this.

The mantle is mostly solid.

Roughly 1% of the mantle is thought to flow like a very thick fluid.

This movement occurs over thousands to millions of years.

So three mistakes you should have picked up there, solid, not liquid, 1%, not 99% and then it's thousands to millions of years.

Yeah, not one to two.

Did you get that right? Well done.

Time for the second part of our lesson now.

We're going to be exploring tectonic plates.

So the upper mantle and the crust combine to make up hard, rigid outer layer of the air called the lithosphere.

The lithosphere is not one continuous layer.

It's actually broken into large sections called tectonic plates.

Aisha's asking, "Which plate is the UK on?" Do you know? A label on the UK for you.

Yes, Andeep says it's "The Eurasian plates and that makes sense because the UK is in Europe," so the Eurasian plates covers Europe and Asia.

If you have a look, there are lots of plates that are named with really sensible names, such as the North American plates, the African plates.

These are all just the names that we probably would give them if we were making names up.

So it does make it a lot easier.

It's a good idea to take a little look at the plate names now, just so you become a little bit more familiar with them.

Where two plates meet, this is referred to as a plate boundary, shown by the red lights on this map.

So the red line that's identified is the plate boundary between the Pacific plates and the NASCAR plates.

All plate boundaries can have earthquakes.

Some occasionally happen away from plate boundaries as well, though those ones tend to be less significant.

Can you name the feature circled in the diagram? Is it A, a plate? B, a plate boundary? Or C, the inner core? Well done, it's a plate boundary.

Right, let's try this one now.

Can you name this feature circles? Well done.

That's plates, very good.

As well as earthquakes, many plate boundaries, not all though experience volcanic eruptions.

There are also a few volcanoes away from the plate boundaries.

So just in the same way that earthquakes happen on the plate boundaries and then there's some earthquakes that happen away from those plate boundaries.

We have a similar thing with volcanoes.

We have a similar pattern.

The only slight difference that I would note is that some plate boundaries don't experience volcanoes.

So there's different types of plate boundaries, some of which do have volcanoes and some of which don't have volcanoes.

You should be able to see this on the map here, where you can see some plate boundaries actually don't have any volcanoes.

Two thirds of the world's volcanoes that erupt, or who have erupted recently are on plate boundaries around the Pacific Ocean.

It is a region known as the Pacific Ring of Fire due to the number of volcanoes.

So that name sort of makes sense as well, doesn't it? Ring of fire is a ring shape and fire because volcanoes look like fire, they're very hot.

You can see here and actually on lots of tectonic maps, that the Pacific Ocean is in the centre of the map.

Now, normally we're used to seeing world maps with the UK and Europe in the centre of the map.

So this is quite an unusual layout for some people to absorb.

So in order to explain that a little bit, I've got a globe here.

Nine in every 10 of the world's earthquakes occur in this region too.

So actually, even though we get earthquakes on every single plate boundary, the ring of fire experiences far, far more than it's fair share of earthquakes.

Can you see the Pacific Ring of Fire on this map? Yeah, Pacific Ocean is here and Pacific Ring of Fire is just here, you see identified by that orange line.

Time for a quick check for understanding.

How explosive was Mount Pinatubo in the Philippines when it erupted in 1991? Can you tell using a key on the left hand side? Well done.

Yes, it was colossal.

Just have to look at the different shades of red there.

Next we're going to look at a task.

So our first part to this task is to define the following key terms, tectonic plate and plate boundary and it's really important to know the difference between those two.

The second part of the task is how many of the seven highest magnitude, so these are strong earthquakes, in 2017 were in the Pacific Ring of Fire? So the magnitude is shown on the map here using circles.

The key shows us that the higher magnitude, the worse earthquakes, the stronger earthquakes are shown with the larger circle and then the smaller circles, increasingly smaller circles show us increasingly weaker earthquakes.

So have a look at the circles on the map to help you identify how many of the seven highest magnitude earthquakes in 2017 were in the Pacific Ring of Fire.

Notice this map is not Pacific centred.

This is actually a map that we would be used to, so make sure you're working out where the Pacific is looking at this map.

The third part of this task is to add the top five highest magnitude earthquakes from 2024 to a world map using this key, so I've given you the magnitude of each of these earthquakes.

I've given you the coordinates of them and the affected country as well.

Try to plot them as accurately as possible using the coordinates.

Fourth part of our task is to describe the distribution of significant volcanic eruptions worldwide.

I'd like you to write a sentence or two on this.

Well done everyone.

Let's take a look at the answers.

For question one, tectonic plates are large, rigid sections of the lithosphere.

This is the crust plus the upper mantle.

Plate boundaries are where two plates needs, so just double check that you've put lithosphere there and not crust, because it is slightly different and we want to make sure that we're getting this accurate.

For your second question, you should have said that there was six of the seven largest earthquakes in 2017 in the Pacific Ring of Fire.

So only one wasn't in the Pacific Ring of fire.

For number three, you should have plotted your earthquakes like this on the map, so you can see where they're located here.

Just check that you did use the coordinates and you did plot them accurately as opposed to just putting them in centre of a country.

Right, the last one was to describe the distribution of significant volcanic eruptions worldwide.

So most volcanic eruptions occur on plate boundaries.

Two thirds of the volcanoes that are currently erupt or have erupted recently are located around the Pacific Ocean in the region called the Pacific Ring of Fire.

Have you the Pacific Ring of Fire? It'd be a good idea to add that in if you've forgotten and it would be a good idea to say specifically that there were two thirds of volcanoes that currently erupt or have erupted recently.

Get it right, get it very specifically right, are located around the Pacific oceans.

So let's remember that two thirds fact as well.

Right time for our summary now.

The Earth is made of four main layers that have different chemical compositions.

We've got the inner core and outer core, the mantle and the crust, together, the upper mantle and the crust form the Earth's rigid outer layer.

This is called the lithosphere.

The lithosphere is broken into large sections or tectonic plates.

Most earthquakes and volcanoes occur at plate boundaries.

I hope you enjoyed the lesson today and discovered something new.

I've certainly enjoyed learning with you.

Thank you very much.

See you next time.