Lesson video

Hello.

My name's Mrs. Niven.

And today, we're going to be talking about Earth's structure as part of our unit on Earth's resources.

And what we talk about in today's lesson, You may have some experience of from your previous learning.

But what we do today will help us to better understand and answer those big questions about how we can explain changes that we see in the air, the oceans, and the land.

By the end of today's lesson, you should hopefully feel more confident being able to describe the structure of Earth.

Throughout the lesson, I'll be referring to some keywords, and these include crust, mantle, outer core, inner core, and model.

Now, the definitions for these keywords are given in sentence form on the next slide, and you may wish to pause the video here, so you can read through them and perhaps make a note of them, so you can refer back to those definitions later on in this lesson or later on in your learning.

So, today's lesson is broken into two parts.

We'll firstly look at outlining what the layers of Earth are called and what they're like, and then we'll look at the models that scientists use to represent Earth's structure.

So, let's get started by learning more about Earth's layers.

One thing to remember is that processes that occur deep under Earth's surface can transform one type of rock into another.

For instance, a sedimentary rock might turn into a metamorphic rock and that could in turn change into an igneous type of rock.

And also these processes could even bring new rock to the surface.

For instance, through an erupting volcano could produce igneous rock.

Now, to better understand how these changes actually occur, we need to take a closer look at Earth's structure.

Now, from space, Earth actually appears as a rocky planet that shaped like a sphere.

Now, if we were able to cut into Earth's structure, we'd be able to see that it's divided into distinct layers, and these include the crust, the mantle, and its core.

And that these layers differ from each other, because of their chemical composition.

So, let's take a closer look.

The outermost layer of Earth is referred to as its crust, and this is where all life is found.

Now, the crust is composed of 93 different elements, but these eight elements comprise over 99% of the crust in total.

Now, the rocky crust is Earth's thinnest and most brittle layer.

And if we were to take a closer look at it, we could see that it varies in thickness of anywhere between 5 kilometres and 70 kilometres thick.

Zooming in even closer, we can see that the crust is going to be thickest on land and it's thinnest under the oceans.

Let's stop here for a quick check.

What's the average thickness of Earth's crust? Well done if you said 35 kilometres.

Remember it ranges in thickness of anywhere between 5 to 70 kilometres thick.

So, if we're looking for the average, we're looking at around about 35 kilometres.

And the units there were really important.

So, very well done if you managed to get that correct, guys.

We are off to a fantastic start.

Keep it up.

Now, below Earth's crust is its mantle.

And compared to the crust, the mantle contains higher amounts of iron, calcium, and magnesium, and that's what gives it its different chemical composition and tells us that it is a different layer entirely from the crust.

Now, the mantle is Earth's thickest layer at around about 2,900 kilometres thick and it's composed of dense rock.

Now, there is some evidence that suggests that specific areas of the mantle around about just less than 1% of it can actually flow like a very thick fluid.

However, this movement or flow occurs over thousands to millions of years.

Let's stop for another quick check.

What is the mantle composed of? Well done if you said C, it's dense rock.

You'd be exactly right.

Now, we did say that parts of the mantle sometimes show liquid-like properties, like its ability to flow, but remember, that's only about 1% of the mantle and it's such a small proportion that the mantle is composed of dense rock.

So, very well done if you've got that correct.

Great job, guys.

Now, beneath the mantle and at Earth's centre is its core, and this part of Earth structure is thought to be mostly composed of a mixture of iron and nickel.

And we can see now that there's a distinct difference between the composition of the crust that remember, had 93 different elements in it, to the core, which we reckon is mostly iron and nickel.

So, just two elements.

Now, evidence suggests that despite its chemical composition, there are actually physical differences found in Earth's core.

The outer core, so that's the bit directly below the mantle, is liquid iron and nickel.

And then, at the direct centre of Earth, so below the outer core is the inner core, is solid iron and nickel.

Now, both of these combined are referred to as the core, because chemically, they have the same composition.

However, we can distinguish between the outer and inner core, because of those different physical states and those exist depending on the depth into the Earth that we are talking about.

Now, radioactive processes in Earth's core generate heat and the temperature of Earth's inner core is estimated to be nearly 5,200 degrees Celsius.

Now, despite that high temperature, Earth's inner core is solid, because of that intense pressure that it's under caused by the layers above it.

What we find then is that the average temperature increases as you travel from Earth's crust towards its core.

Let's stop here for a quick check.

True or false, the temperature at the bottom of the deepest working mine, which is just under four kilometres deep, is cooler than an Earth's surface.

Well done if you said false, but which of these statements best justifies that answer? Well done if you said B, Earth's centre is very hot, and as we travel from Earth's crust towards its core, the temperature is increasing.

Now, if you were tempted to say that rock is very cold, because you've had experience going into caves or down mines, things like that, those rocks tend to feel cold, because they've not yet been warmed and usually by the sun.

But the further into Earth's cross that you travel, the temperature does increase on average.

So, well done if you managed to get that correct.

Well done.

Let's have a go at the first task of today's lesson now.

In this first part, I'd like you to match the keywords to the best description.

So, pause the video and come back when you're ready to check your answers.

Let's see how you got on.

The crust is about 5 to 70 kilometres deep and is rather brittle.

And Earth contains three distinct layers that are distinguished by their chemical composition.

The outer core is located deeper than the mantle and is composed of liquid iron and nickel.

The mantle is Earth's thickest layer, it's dense rock, and around about 1% of it can flow like a thick liquid.

The inner core then is Earth's deepest layer and it's composed mostly of solid iron and nickel.

So, very well done if you manage to match those up correctly, guys.

You're off to a flying start.

Keep it up.

For the next part of this task, I'd like us to look at scale diagrams, because they're very useful in helping us to visualise and compare layers in an object.

So, the first thing I'd like you to do is use information provided in the table below to create a scale diagram of Earth's structure.

And to help you with that, I've provided you the scales and almost like a wedge section of the Earth.

And then, I'd like you to label each section appropriately.

So, take a moment, pause the video, and come back when you're ready to check your work.

Okay, let's see how you got on.

Now, if you've done this correctly and starting at the very bottom of our scale diagram, so the centre of the Earth point, we should have started with the inner core showing the thickness of about 1,250 kilometres.

You then needed to add on to that number, 2,200, which is the thickness for our outer core.

Onto that, we would add the thickness of the mantle, and then finally the crust.

So, there is a temptation to put lines in that match the thickness of our table, but those numbers needed to be added on top of each other to show the thickness of each of those layers.

So, do take a moment to double check that you have put the lines in the correct position according to the scale that's been provided for the thickness of each of Earth's layers.

But very well done if you've managed to get that correct.

Great job, guys.

For this next part then, I'd like you just to consider the scale that's now been drawn.

What is one way in which this scale diagram might be improved to make it look more like a slice of Earth? So, pause the video, maybe discuss some of your ideas with those nearest you, and come back when you're ready to check your answers.

Okay, let's see how you got on.

One of the easiest things you could potentially suggest here is to maybe use a compass or a curved line to help you distinguish each layer from the next to help show that spherical nature of Earth's structure.

So, we're going from the straight lines to a slightly curved line to indicate that spherical nature within this slice of our diagram.

Very well done if you've managed to suggest that improvement to our scale diagram.

And for the last part of this task that I'd like you to go back to the information that was matched up in task A, part one, and I'd like you to use that to add one additional detail to each layer of our scale diagram of Earth's structure.

So, pause the video and come back when you're ready to check your work.

So, for this one then, all you needed to do was copy up some of the information from task A, part one, and pop it into our scale diagram.

So, for the crust, you could have added either that it's brittle or that it is 5 to 70 kilometres thick.

Well done if you managed to add both.

For the mantle, again, you could have said that it was dense rock or that around about 1% can flow like a thick fluid.

For the outer core, you could have said that it's composed of liquid iron and nickel.

And the inner core then is composed of solid iron and nickel.

So, now, we have a completed scale diagram for Earth's structure, including some of its properties.

So, very, very well done.

Now that we're feeling more comfortable discussing the different layers of Earth's structure, let's move on to discuss the models that are used to represent Earth's structure.

Now, some of you may have heard of a borehole before.

Now, a borehole is simply a narrow shaft that's drilled into an object for a variety of reasons.

For instance, you might be able to use a borehole to access resources like oil or water that's underground or they may bore a hole into perhaps a glacier or an ice cap in order to collect material for analysis.

Now, the deepest that humans have ever managed to drill on Earth was known as the Kola Superdeep Borehole, and this was drilled in Russia.

It managed to reach a depth of 12,262 metres.

Now, the Kola Superdeep Borehole pierced into only 18% of Earth's crust.

So, let's take a closer look at what that means.

If you think of the highest point on Earth is the tip of Mount Everest, and that exists just under nine kilometres from sea level, the deepest working mine is just under four kilometres into Earth's crust, and the lowest point of the ocean is just under 11 kilometres deep, the Mariana Trench.

The Kola Borehole went deeper, 12.

3 kilometres deep and still that is only 18% of Earth's crust.

Because of this, scientists can't say with any certainty what the structure of Earth actually looks like or what it's composed of.

So, what scientists have done of collected evidence, for instance, from earthquakes, and used it to develop theories about the structure of Earth's interior, and then to build a model from that evidence.

Now, this isn't a new idea.

Scientists use models all the time to help explain phenomena that cannot be easily seen.

For instance, we might use a model solar system, because some of the objects in it are simply too large to see.

We might also use a model molecule, because the atoms in it are far too small to see.

Now, models also help scientists better understand complex systems, things like the model ear, where there are many different parts that work together to convert these sound waves that are collected into something that we can understand and interpret in our brains.

And also to better observe different processes.

For instance, how the diaphragm impacts the function of the lungs during the process of breathing.

So, models help scientists to do many things.

If we can better understand processes, we can use these models then to also make predictions.

If we change one part of the process, how might that affect another part of the process? And it also helps us then to communicate those ideas to others.

Let's stop here then for a quick check.

Which of the following is not a reason why scientists use models? Well done if you said B.

We would not use a model in place of an experiment.

So, well done if you managed to get that correct, guys.

Great job.

Now, while these models will help scientists to better understand processes, communicating those ideas, and making predictions, models have limitations, and it's really important that we consider those limitations when we decide whether or not a proposed model is useful.

Let's consider an apple, for instance, if it was used as a model of Earth structure.

What might be an advantage and what might be a disadvantage of this model? Well, there's a variety of things we could say.

For instance, an apple has a thin outer layer, a thick middle layer, and it shows a core just like the three parts or main parts of Earth's structure.

But there are limitations to this model.

For instance, it's not spherical like Earth.

And the core is far too small compared to Earth's core.

Let's consider then a Scotch egg.

What is one advantage and a disadvantage of using it as a model of Earth's structure? Now, you may wish to discuss some ideas with those around you.

So, do pause the video and come back when you're ready to check your answers.

Okay, let's see how you got on.

Well, some of your answers may have included that it had a thin outer layer, a thick middle layer, and it definitely shows a core.

However, there's no layer for it to be showing the outer or inner core, and it's not spherical again, just like our apple.

So, there are pros and cons to using this particular model to represent Earth's structure, but very well done if you've got at least one advantage and one disadvantage for using this model.

Great job, guys.

Okay, let's move on to the last task of today's lesson.

Some students have decided to use a hard boiled egg as a model of Earth's structure, and we have labelled it here.

So, we are talking about an egg shell, the egg white, and its yolk.

I'd like you to state three ways in which this is an accurate representation of Earth's structure and three ways in which it is not an accurate representation of Earth's structure.

So, definitely pause the video whilst you discuss your ideas with those nearest you, and then come back when you're ready to check your answers.

Okay, let's see how you got on.

So, for part A, I wanted you to tell me what was good about this model of Earth's structure, and there were a lots of different things that you could have said.

So, did you get three of the following? One thing you could have said is that it has three distinct layers that could correspond to Earth's crust, mantle, and core.

And the eggshell is very thin, just like the crust is on Earth.

And the egg white is dense just like the mantle is on Earth.

The next thing I asked you to do was to state some ways in which this model might not be an accurate representation of Earth's structure.

And there are again, a variety of things you could have said, but these are the ones that I came up with.

So, your answer may have included things like the egg is still not an approximate sphere like Earth is.

So, this spherical nature of Earth is quite tricky for us to get in our models at the moment.

We could also say something about the shell being about the same thickness all around the egg.

And if you remember, if that's representing our crust, the crust actually varies quite significantly.

Remember we said it could go anywhere between 5 and 70 kilometres thick, and we don't get that variety in thickness in an egg shell.

The yolk is not in the centre of the egg just as Earth's core is, so it's a little off centre there.

Earth's core has a solid centre, but the outer core is liquid and that isn't shown in our egg model.

And finally, the centre of the egg is not hot just like Earth's core is.

So, there are a variety of things that are quite useful about this model, but there are also several limitations to this model.

And these are all things that we need to consider when we're going to use a model to help us to better understand the structure, process of various scientific theories and ideas.

But very, very well done.

Being able to evaluate models like this about what is good and maybe not so good about them is a very tricky task.

So, even if you only got one or two ways in terms of identifying what was an accurate or not accurate representation of Earth structure using this egg model, give yourself a pat on the back, 'cause not an easy thing to do and I'm really proud of the effort you've put in.

Well done.

Well, we have gone through a lot of information in today's lesson, so let's take a moment to summarise what we've learned.

Well, we learned that Earth is a spherical rocky planet that can consists of a thin crust that's partially covered in water.

And that under the crust, the Earth has a dense, rocky layer that's called the mantle, and very small proportions of it can move like a thick fluid under certain conditions.

And at the very centre of Earth is a solid metal core that's surrounded by a liquid outer core.

And the temperature and pressure increases towards the centre of the Earth, making the inner core extremely hot and solid.

And we've also learned then that scientists use models to better understand phenomena and that includes Earth's structure.

I've had a great time learning with you today and I hope you've had a good time learning with me.

I hope to see you again soon.

Bye for now.