﻿Hi, my name's Miss Earthrowl and welcome to lesson three in the Key Stage 3 unit of work on plate tectonics. Today we're going to be looking at how those tectonic plates, those big slabs of rock that form the Earth's crust actually move and what the driving force is behind that movement. For today's lesson you'll need a pen and a pencil, you'll also need a piece of paper or an exercise book to write in. Try and find yourself a quiet space away from any distractions so that you can focus on your learning. So get those items, get yourself ready, and press play when you're all set. Welcome back, so we need to think about this question, how do the Earth's tectonic plates move? What's the driving force behind that motion? To help us understand, we need to look at the structure of the Earth. The Earth's crust is solid and is broken up into large pieces of rock called tectonic plates. These tectonic plates float on top of the semi-molten or semi-liquid mantle. The temperature increases as you move towards the centre of the Earth, this is because the Earth's inner core is the Earth's hottest layer. So what happens in the mantle to make these tectonic plates moves? Remember those tectonic plates are floating on top of the mantle and it's what's going on underneath that's the driving force behind that movement. We get convection currents. Convection currents are currents in the Earth's mantle which rise from the Earth's core and are strong enough to move those tectonic plates. If you want to write down that definition, then please pause the video now. Great. You can also see the convection currents in this diagram here, taking place in the mantle. So how do convection currents work? I'm going to show you this video and talk you through the process. I'm very excited to be able to share with you this video from the Esri website, it's going to show us a slice through the Earth's surface, as you can see here, so that we can see what's going on to help us visualise that motion in the mantle of the convection currents. So watch and listen carefully to find out how the process works.

It happens because hot rock rises, heated by the Earth's core. Near the surface, the rock spreads in two directions and goes sideways, it begins to lose heat, eventually, the much cooler rock sinks back down. Through this spreading process, the Earth's crust is very slowly dragged apart.

If I pause this video here, it shows us a great animation of those convection currents. You can see the core down at the bottom which is in the middle of the Earth and you can see this is heating those pockets of molten rock above it and they're rising towards the surface and the Earth's crust. You can then see that they're forced to spread sideways and as they do so, they drag those plate tectonics with them. They then start to cool down and sink back down towards the core, ready to start the process again. Hopefully that video insert has given you a little bit more of an idea of what's going on in the Earth's mantle to drive this tectonic plate movement. But let's walk through this process of convection currents. So the Earth's core heats up the rock in the lower mantle, you can see on the diagram below, that we've got the core represented in red in the middle of the Earth and the mantle around it. As the rock in the lower mantle melts and expands as it gets heated. This pocket of heated, molten liquid rock is less dense and lighter than the surrounding rock so it rises away from the core. You can see the hot, less dense liquid rock rising on this diagram, represented by the arrows. As this molten rock rises, it reaches the crust and it spreads sideways. The thick, viscous, molten rock is very sticky and so it sticks to the bottom of those tectonic plates and drags them along with it. You can see on the diagram the tectonic plates being dragged apart. As the molten rock is now further away from the heat source and it's been there for a little while, it's started to cool down again and become denser or heavier. This means that as it's cooler and heavier, it sinks back down towards the core, completing that convection cell. Again, you can see the arrows represented on the diagram. When those pockets of molten rock are red hot, you can see that you've got red arrows where they're rising away from the core and then moving sideways, but they start to cool down and when it's cooler, those arrows are represented in orange until it gets back down to the core and the whole process starts again. So let's have a think about what you've remembered, I want you to read through these statements and put the following statements in the correct order to explain the process of convection currents in the mantle. To help you out, the first and the last are correct and highlighted in pink. I want you to pause the video to complete your task. Excellent, well done for having a go, let's see if you've managed to get the order of the process correct. So we know that the two pink statements are right. The core heats up the rock in the lower mantle is the starting point. The next point is C, the rock in the lower mantle melts and expands as it gets heated, well done, give yourself a tick if you managed to put that next. Then we have B, pockets of heated, molten, liquid rock are less dense or lighter than the surrounding rock so they rise away from the heat of the core. As the molten rock rises, it reaches the crust and spreads sideways as the thick, viscous, molten rock sticks to the bottom of the plate, it drags it along with it. Then we have D, as the molten rock is further away from the heat of the core, it cools and becomes denser, heavier. And then we know that F was the final piece, as it becomes heavier, it sinks back down towards the core, ready to be heated again. If you want to, you can pause the video to make sure that you've got those statements written in the correct order, give yourself a tick if you've managed to get it right and well done. Now, it's not just the convection currents that are though to move the Earth's tectonic plates. They're a very important part of the process, but we also have slab pull and ridge push. Let's watch this video to see if we can work out what ridge push and slab pull are. If we watch a little bit more of this video, we can see not only the important role that the convection currents have on tectonic plate movement, but also those other two key terms, ridge push and slab pull.

It happens because hot rock rises, heated by the Earth's core.

If I pause the video here, we can start to think about what ridge push is. You can see that as the magma rises, it pushes up through the cracks in the Earth's surface and comes out in a line of volcanoes and solidifies to form what we call a ridge. As this pushes up and as it solidifies, it actually has another process and it pushes those plates apart, contributing to their movement and that's what we call ridge push.

Surface, the rock spreads in two directions and goes sideways. It begins to lose heat.

If I pause the video again, we can talk about the other process, yes we have convection currents dragging those plates apart because of that hot, sticky, viscous, thick magma, but also, the plate being dragged apart is what we call oceanic crust and oceanic crust is known to be denser and heavier than the other crust, continental crust. As it starts to plunge down into the mantle, as we can see here, it's not only being dragged down by the convection current, but it's also being pulled down because of gravity. Because it's much heavier and denser, therefore gravity acts on it to pull it down more into the mantle, fueling and driving that process of the movement of tectonic plates. So hopefully you can now understand that there are three different processes taking place that cause that movement of the tectonic plates. We've got our convection currents in the mantle, we've then got ridge push which is where as the magma comes up towards the crust, it starts to form a ridge which pushes those plates apart and the third one is slab pull. Slab pull is where you've got a really heavy, dense, oceanic crust and because it's weightier or heavier than the other crust and the mantle, as it sinks back down, it forces its way, plunging into the mantle because of the weight. So let's see what you've learnt. I'd like you to draw an annotated diagram to show ridge push and slab pull. I want you to draw both features clearly and annotate the diagram to explain the process of ridge push and slab pull. Now, when you annotate something it means that you're providing much more detail than a simple label, you're almost writing full sentences to explain the process. To help you out, I've put some words at the bottom, I want you to use the words below to help you explain how each of those processes work. Now remember, you're writing these in full sentences. I've also put some numbers onto the diagram to help you, for each of these numbers, I expect you to write a full sentence to explain that particular part of the process. One, two, and three refer to ridge push, whereas four refers to slab pull. So pause the video now to complete your task and don't forget to press resume when you're done. Welcome back, so let's see, did you get it? I've put the diagram here where we can see the oceanic crust and the continental crust, I've also labelled the mantle and put an arrow on to show the direction that the force of gravity is working in, this will help you to explain. So let's see what goes at number one, we have rising magma, now you can give yourself a tick if you've written rising magma here, but you can give yourself an extra tick if you've added in some full sentence information about why that magma is rising. Number two, lava erupts and solidifies as a ridge. That's the second part of the ridge push process, give yourself a tick if you've managed to write that or similar down. And thirdly, the plates are pushed apart, this is because if the lava solidifies, it actually acts on pushing that and fueling the process of the movement of the tectonic plates. We then move onto slab pull, ooh, sorry, to label that, that's ridge push, the process that pushes the plates apart. The second process, gravity pulls the dense, oceanic plate downwards. You can give yourself a tick if you've got this right, you might even have added some extra information, if you have, give yourself an extra tick. You can also give yourself a tick for labelling this process as slab pull. So we have those three main processes that help us explain how the Earth's tectonic plates move. We have the convection currents in the mantle, fueled by the heat of the core, causing the magma to become heated, less dense, and rise towards the crust and then get spread apart and as it does so, it pulls those tectonic plates with it. Secondly, we have ridge push which as that rising magma comes towards the crust, it forms a ridge, pushing those plates further apart. And finally, we have slab pull, because the oceanic crust is dense and heavy, gravity acts on it as it starts to go into the mantle, further pulling it down to become subducted in the mantle. Well done for all of the effort that you've put into today's lesson. In next lesson, we'll be looking at the different types of plate boundary and I hope to see you then. Share your work with Oak National, if you'd like to, please ask your parent or carer to share your work on Instagram, Facebook, or Twitter tagging @planetearthrowl, @oaknational and #LearnWithOak.

This lesson will look at how the Earth's plates move by convection currents, slab pull and ridge push.

There are different causes of plate movement: convection currents, slab pull, ridge push.

Geography

Y8 Geography

Key Stage 3

Year 8

Miss

How do the Earth's plates move?

Tectonics

UNIT

What is the structure of the Earth?

What evidence is there that the Earth's crust moves?

What are the different plate boundaries?

What are composite and shield volcanoes?

How can we predict, protect and prepare for volcanic eruptions?

What are the positive and negative impacts of volcanoes?

How can we measure and predict earthquakes?

How can we prepare and protect against the impact of earthquakes?

Where is Haiti and what is it like?

What happened in the 2010 Haiti earthquake?

What are tsunamis and how do they form?

Where is Japan and what is it like?

What happened during the 2011 Japanese tsunami?

What were the responses to the 2011 Japanese earthquake and tsunami?


The following question is about the structure of the Earth

The Earth has...

Select the correct order from the outermost layer of the Earth to the centre.

Choose the three correct statements. The Earth's crust is...

Convection currents are...

Convection currents cause the tectonic plates to move because...

Slab pull happens...

The 2011 earthquake in Japan triggered a tsunami. A tsunami is...

An example of a long-term response is...

A tsunami is can be caused by...

Haiti shares the Caribbean island of Hispaniola with...

A developing country often experiences a higher number of deaths when an earthquake strikes. This is because...

Lesson overview:How do the Earth's plates move?

Core Content

Pupils Will Learn

Tectonics: