Lesson video

Today, we are going to look at how do the rocks on our Earth's surface change? So we've learned all about how rocks are made, how rocks are formed.

We've learned about three types of rock and how they're formed, and we've learned how to identify those types of rock.

But when a piece of metamorphic rock or sedimentary rock or igneous rock is made, it doesn't just stay that way forever.

The rocks on our Earth's surface are constantly changing, okay, and we're going to learn about how and why they change in today's lesson.

For today's lesson, we are going to need a piece of paper, a pencil, a colouring pencil, and a ruler.

We might not need a ruler.

I can't remember.

Get a ruler just in case because if we draw any diagrams, we'll have to do our labels.

But I might be giving you a bit of a trick there.

We'll have to see.

We're going to need three star words for today's lesson.

The first is magma.

My turn, magma.

Your turn.

Magma, we have learned about before.

Magma is molten rock, so it's like a liquid rock that has melted, okay? Magma is molten rock.

We're also going to need the star words weathering and erosion, but those are two new star words.

So we'll learn those during our lesson.

Let's start with our recap.

We are in our fifth lesson of this unit on rocks now.

So lots of this information, you are going to know really well already.

If you're joining us late, and you've missed out some of our earlier lessons, then that's okay because you can go back to the lessons on the Oak National website, and you can catch up when you find yourself with some spare time.

So, a rock is made of solid grains that fit together.

We've learned about three main types of rock.

If you know them, say them to your screen, igneous, sedimentary, and metamorphic rock.

And we've learned about how each of those types of rock are made.

Well done if you got these correct in your pre-lesson quiz.

If not, that's okay, 'cause that's why we're going through them now.

So igneous rock is formed when magma or lava cools and solidifies.

Metamorphic rock is our next one.

Here's a picture to remind you.

Metamorphic rock is formed when pressure or heat inside the Earth change sedimentary or igneous rock.

So to get metamorphic rock, we need to start with sedimentary or igneous rock.

And sedimentary rock, here's the picture to remind you, is formed when pressure from layers of sediment causes the sediment to compact and cement.

So, as we've already mentioned, the Earth's rocks do not stay the same forever.

They are continually changing because of processes, such as weathering, erosion, and large Earth movements.

We're going to look at all three of those this lesson, and we're going to start with weathering.

So look at these pictures.

Here are some pebbles.

And here are grains of sand.

How do you think these pebbles and grains of sand are made? Now, they would've originally started as metamorphic, sedimentary, or igneous, and they would've been made in those ways that we've learned.

But how do they get from a big slab of rock to these small, smooth pebbles or even smaller, teeny-tiny grains of sand? That's what we're going to learn about today, okay? I'm going to start by showing you a demonstration that explains one way that this can happen.

For this demonstration, I'm only going to need three things.

I need a plastic transparent container.

I need some water, which I've got here in a jug.

It's just water from the tap.

And I need a permanent marker, okay? I'm going to set up this experiment, and then we're going to fast forward in time to later on to see the results of it.

So to set up this experiment, what I'm going to do is I'm going to pour some water in my plastic container, so it's about half full.

Then I'm going to take my Sharpie, my permanent marker, and I'm just going to get down to eye level, and I'm going to draw a line.

Whoop, I've just knocked my box, it's not straight.

I'm going to draw a line right where my water is.

I'm going to turn it around in a second, so you can see really clearly.

Okay? So, there you go.

You can see, I've drawn a kind of squiggly line where my water is.

If I hold it straight, you'll actually be able to see.

There you go.

So there's my line.

I'm now going to take this, and I'm going to put it in my freezer.

So here is our cup of ice that I put in the freezer yesterday.

So you can see the blue line is where our water level was when we put it in the freezer yesterday.

And you can see that the ice has risen above that line.

Now, I'm just actually going to take a different coloured Sharpie, and I'm going to draw where the new, I chose the wrong colour.

You can't see that one easier.

Give me a sec.

Okay, fingers crossed.

Here we go.

Yes, this one works.

I'm going to show you, I've drawn a line, so everybody can see really clearly.

This is where our waterline was when it was a liquid.

And then after we put it in the freezer, and the ice is frozen, this black line is where our ice line is.

So the ice has expanded as it's frozen.

It's gotten bigger.

If you want to try this out for yourself at home, you can.

Rule number one of demonstrations is that you always need to check with a parent or carer before you try them.

And make sure that your container is plastic.

If you use glass, then it might break.

So, let's think about what we saw in that demonstration.

When water freezes into ice, it expands, it gets bigger.

And we saw that happening on our cup.

Now, rocks, lots of rock types have little holes or gaps in them, depending on the rock might depend on the size of the holes.

This is a picture of one where it's quite obvious, but even rocks that look quite smooth would have small holes and pores in them.

So what do you think would happen if water soaked into the rock, like it does with a sponge, and filled up those holes, and then that water froze? What do you think would happen? Well, the same thing would happen that happened in our demo, that ice would expand, and that could cause the rock to crack or break into pieces.

So here's a picture where this has happened.

This great big rock has cracked in half, and it's all because of ice freezing.

So you might want to make some notes while I'm talking about weathering.

So that's our first type of weathering.

Weathering is when we break big rocks into smaller pieces.

What's weathering, say it to your screen? Great, big rocks into smaller pieces, okay? And this is our first type, when ice expands.

There's another type of weathering called chemical weathering.

So that's what's happening on this rock here.

Chemical weathering is when chemicals, so acids in water, start to dissolve the rock.

So what's chemical weathering, repeat it back to me? When acids in the rain start to dissolve the rock.

What's chemical weathering? Great, when acids in the rain start to dissolve the rock.

There's another type of weathering, which is called biological weathering, which is basically when plants or animals cause the rock to break up into little pieces.

So here, you can see the tree root has grown into the rock and has caused it to crack open.

Here's an example, not with a plant as big as a tree, but you can see some smaller bushy plants are starting to grow in between the cracks in the rock and split them apart.

So this is our definition of weathering, just to summarise.

It's the process where rock is broken into smaller and smaller pieces, say it with me, the process where rock is broken into smaller and smaller pieces.

And we saw a couple different examples of how this could happen.

It could happen with chemicals in the rainwater, it could happen with plants growing into cracks in the rock, and it could happen when water freezes in holes or gaps in the rock.

I've got some questions for you now.

Here are your questions.

What is weathering, and can you draw a diagram to support your answer? And give three examples of things that can cause weathering.

Please pause the video and answer those questions for me now.

Great, good job, everybody.

Let's see if you got the same answers as me.

So number one, weathering is the process where rock is broken down into smaller and smaller pieces, and you might have drawn a diagram a bit like mine.

Number two, these were some of the ways that weathering can occur, plants, water freezing and expanding, and chemicals in water.

Well done if you got those correct.

If you need to make an adjustment to any of your answers, that's okay, just pause the video and complete that now.

Great.

The next thing we're going to learn about is something called erosion, practise saying that word with me, erosion.

I'm going to show you a demonstration to explain what erosion is now.

In this demonstration, I'm going to show you something that will hopefully help to explain the process of erosion.

Okay, so I'm going to use a plastic bottle, transparent, so I can see clearly what's going on.

This is a stock cube, so you might have these in your kitchen to help with cooking, and some nuts.

So I'm just going to unwrap this.

My stock cube represents a softer rock, okay? When we learned about metamorphic rock, we learned about some different types of metamorphic rock, and we learned that some of them are harder than others.

So we kind of think of rocks always as being hard, but in comparison to each other, they're not all as hard as each other.

So this is a soft rock, the kind of rock that you could probably scratch with your nail, okay? It's still solid.

It's still a solid piece of rock.

So that represents my softer rock.

I'm going to get rid of that wrapper.

These nuts represent a harder type of rock.

Okay? Now, my plastic bottle is going to represent a river.

So I'm going to put my hard rocks and my soft rock in my river.

Now, when water moves along a river, it moves around a lot, and that causes the rocks and the pebbles and the stones and all the bits and bobs that are in the water to move around a lot too, okay? So now I'm going to shake this plastic bottle.

It's probably going to make a loud noise.

And I'm going to simulate, I'm going to show you what would happen when our stones and our river water move around a lot, okay? So before I start, just have a look.

We've got our soft rocks and our hard rocks in there.

And now I'm going to move my river water around as if my river is flowing down its stream.

Okay, I had to shake it for a long time.

I had to shake it quite hard, but I can now show you what's happened.

So you can see that the big rocks have stayed intact, have stayed whole, but my softer rocks have broken up into little pieces.

So let me show you on the plate what that looks like.

So you can see here that my stock cube that represents my softer rock has now broken up into lots of little pieces.

Okay, so that's what happens when erosion occurs.

My bottle is representing my river.

So my soft rock and my hard rock would be moving along with my river.

And as my river is transporting my soft and my hard rock, it's causing it to break into small pieces, okay? So that's what erosion is.

It's when rock is transported from one location to another, and this is what's happened, this is what happens while it's being transported, okay? It's all being knocked together by the moving water, and it causes it to break into little pieces.

Now, you can try this at home if you want.

Rule number one for trying demonstrations at home is always to ask parents or carers first, please.

If you do, you'll need some sort of container to shake your rocks about in.

And you can use the same ingredients that I did.

You can use nuts and chicken stock.

The added bonus of that is that your fingers smell like chicken.

However, you can use different things.

You can try out some different things and see what works best.

My tips would be they both need to be a solid because rocks are solid, and one needs to be softer than the other so that it can break apart.

So other things you could maybe try are things like rice for your hard rock, or maybe you could use actual gravel if you have any of that around you.

And for your soft rock, you could maybe try something like a sugar cube.

I think a sugar cube would break up quite well.

But have a go and see if you can model erosion for yourself.

So in that demonstration, we saw an example of what happens when erosion occurs.

So we saw that the softer type of rock was being broken into smaller pieces by the harder type of rock as it was moving through a river, okay? Now, the difference between weathering and erosion is that weathering breaks rock into smaller pieces, but it does it in just one place, okay? So that ice was melting in one place.

Those roots were breaking the rock in one place.

Erosion involves the pieces of rock moving.

So in my demonstration and in this example, the rock is being transported by water through a river.

And as it's flowing through the river, the rock is changing, okay? It might be bumping into other rocks and becoming smaller, like in the demonstration.

So if we were to think about both of those together, a rock might be weathered first.

So it might break into smaller pieces caused by ice or plant roots.

And then it would be picked up by water, so maybe those smaller pieces would be washed into a river and then moved by the river.

It would move along with the water.

And this is called erosion.

Why do you think pebbles are so smooth? Give you a hint, it has something to do with erosion.

So if we think of sandpaper, that might help us think why pebbles are so smooth.

So just like in the demonstration, where my softer rock was breaking up into pieces, those bigger pieces of rock, if I were to keep shaking that motion and keep moving them along my river, they would become smoother and smoother over time because those smaller pieces of rock, which might represent particles of sand, act a bit like sandpaper.

And they rub across the bigger pieces over and over and over again, smoothing them out, which is why pebbles are so smooth.

They're polished by small rocks, and they're polished by the water into smooth and round shapes.

So erosion can help to make smaller pieces of rock and also to smooth pieces of rock.

But erosion is also responsible for some of the big landforms that we might be familiar with from our geography lessons.

So here we have a V-shaped valley.

So you can see, there's a V shape in the valley, and the river has eroded through the valley, okay? So the water travelling through the valley has cut through the rock.

So it's caused the shape of the rock to change.

We also find erosion on the coast, where the sea meets the land.

So erosion by rivers, sorry, erosion by the sea can cause landforms like this.

The waves constantly hitting at the rock cause pieces of it to be worn away.

So that archway that you see didn't used to be there.

It used to be all one piece of rock.

But the rock that was in the archway was softer, so each time the waves and the water from the waves hit it, it started to wear away until it left a hole.

So these are things you might be familiar with in your geography learning, but they're an important part of the rock cycle as well.

In the next lesson, we're going to join everything up and learn about the whole cycle.

Whoop, I've just gone backwards.

There we go, okay.

So erosion, let's learn our definition.

Erosion is the processes that remove rock from one location and transport it to another.

So you can see, our diagram here is showing our pieces of rock.

So in weathering, we start with a big piece, and then we break it into smaller pieces.

And then in erosion, we transport those smaller pieces to a different place, okay? So weathering, erosion.

Okay, we can do our action, do it with me, weathering breaks our rock into small pieces, and erosion transports them to different places.

I have some questions for you.

Can you please answer these questions? What is erosion, and what is the main difference between erosion and weathering? Pause the video and complete those questions for me now, please.

Great, let's check your answers.

Erosion is the processes that remove rock from one location and then transport it to another location.

And number two, weathering happens in one place, and erosion involves movement or transporting, okay? That's the main difference between the two.

Well done, you are working really hard.

We have one way to learn about, one more way to learn about, and that's large Earth movements.

So we're going to recap the structure of the Earth from the first lesson in this unit.

So I want to see if you can remember what each of these labels are.

Remember, we had a sticky way of remembering the layer on the outside that's labelled A.

It had something to do with your bread that you might eat.

Think about what's on the outside of your bread or your piece of toast.

And pause the video and see what you can remember for me, please.

Great, let's check your answers.

So, A was the crust.

We find the crust on the outside of our breath, breath, sorry, the outside of our bread and also the outside of the Earth.

And crust is made of solid rock.

Then our next level was mantle.

The mantle is made of magma.

That was one of our star words at the beginning of the lesson, and it's molten rock.

Then we have the outer core, and then lastly, the inner core.

We're going to focus on the crust, which is made of rock.

And we're going to think about how the rock on the crust can change.

Now, this is something else you might have covered in your geography lessons.

The crust is not just one solid piece of rock.

It's made of lots of different pieces of rock called tectonic plates, okay? So it looks a bit like a jigsaw puzzle.

And you can see this map here has got the tectonic plates outlined on it.

Now, each of these tectonic plates can move slightly because they're floating on the molten rock in the mantle.

So they move slightly.

This is a picture of a place in Iceland called Pingvellir.

I think I'm saying that right.

And it is a plate boundary.

That's what we call the gap where two plates meet.

Now, you don't always see it as a gap, but you can in Pingvellir in Iceland, which is why I've shown you this picture, to help us visualise, okay? So this is where two plates meet.

Now, because these plates are moving, these movements can cause the rock near these plate boundaries to change.

There's a couple ways that this can happen.

The first way is this diagram, is what this diagram is showing us.

So you can see, we have two plates, and the arrows show that they are moving apart, like this.

What is going to happen when they move apart? Think about what is underneath them.

What's underneath them is magma, so that magma is going to come up to the surface, and it's going to solidify when it gets to the surface.

So what kind of rock do you think is being formed at this point? What kind of rock is made when magma solidifies? If you know it, say it to your screen.

Igneous rock, great, okay? So here, we have two plates moving apart, and more rock is being formed.

Igneous rock is coming to the surface.

So that's one way.

A second thing that can happen at plates is that one plate might go underneath the other plate.

So this plate goes like this, and this plate goes underneath.

So what is happening to the rock at this point? Well, the solid crust is going underneath the other piece of solid crust.

And as it goes into the mantle, it gets hot, and it melts into molten rock.

And then this is our last way.

So the same thing is happening here at our plates.

We've got one is going underneath, and one is going up.

But here, our plate that's going up is forming a mountain, okay? The rock is getting squished up like this, and it's forming a mountain.

So that's three ways that rocks can change at a plate boundary.

We can spread our plate boundaries apart, and more rock is made to fill those gaps.

One of our plates might move underneath the other and might melt into the magma.

And one of our plates might come on top of the other and become bunched up into a mountain.

Okay, here are your questions.

Number one, what is the crust made of? Number two, what is the mantle made of? And three, can you draw a diagram to show one way that rock can change at a plate boundary? So you might want to go back to our diagrams that we've just gone through.

And when you draw that diagram, I'd like you to write a sentence underneath explaining what is happening.

You can pause the video and complete that now.

Great, let's check your answers.

So you may have written something like this.

The crust is made of solid rock.

The mantle is made of molten rock.

And, well, you could've written magma for that.

No, could you? Isn't that what the question is? No, you could've written magma for that as well.

And then for number three, you might have drawn one of these diagrams. If you've made a mistake, no problem.

That means your brain has just got bigger.

You can pause the video and correct your answer for me now.

Great, well done.

You have worked really hard this lesson.

I hope that you've made some good notes on erosion and weathering and large Earth movements because next lesson, we are going to put everything we've learned into the rock cycle.

So we're going to put how each type of rock is made and then the processes like weathering and erosion that happen in between them.

We're also going to use Jelly Babies in order to demonstrate this.

I'm really excited.

I hope you have an awesome rest of your day.

And I will see you next week.

Just before you go, sorry, I nearly forgot, here are our star words.

We're going to recap them quickly, so you've got them fresh in your brain when you go and do your post-lesson quiz.

Magma is molten rock.

Weathering is when we break rock into smaller and smaller pieces.

And erosion is when we transport pieces of rock from one place to another.

Well done, again.

If you would like to send me any photos of your work, I always love to see them, but please ask a parent or a carer to send these for you.

And they can send them on Twitter with the hashtag #LearnWithOak or tagging Oak National, and then I will be able to see them.

Have a brilliant day, everybody, and I will see you soon, bye!.