Lesson video

Hi, geographers, my name's Ms. Hoggett, and I'm really excited you're here to learn some geography with me today.

I'm sure if you try your best, you're going to be absolutely fantastic.

Don't worry too much if you haven't studied this topic before.

I'm here to help you every step of the way.

Our title for today's lesson is the rock cycle and this sits within the unit, Rocks, Weathering, and Soil: Why is Geology Important? Our learning outcome for today is that I can identify the three main types of rocks and how they're formed by different processes.

To help us through today's lesson, we have a number of keywords that are going to be really useful to us.

Rock, weathering process, erosion, pressure.

Rock is the solid mineral material forming part of the surface of earth.

Weathering is the process of being worn down due to exposure to the atmosphere.

Process, a process is an ordered series of actions, events, or changes that make something happen.

Erosion is the process of earth's surface, e.

g.

rock or soil, being worn away.

And pressure is a force pushing or pressing on a given area.

So rock, weathering, process, erosion, and pressure are going to be really useful to us in today's lesson.

This lesson is split into two learning cycles.

The first one, the three types of rock, and the second understanding the rock cycle.

We are going to start with our first learning cycle now, the three types of rock.

So earth is split into different layers.

The outer layer, the crust is made of rocks.

Rocks are solids that are made of grains and different minerals that all fit together.

On the image on the screen, you can see we have the layers of the earth, and if we move from inside out, we can see we have the inner core surrounded by the outer core, then the mantle, then the crust.

So we can see that the earth is split into different layers.

Now there are three main types of rock found on earth, igneous rocks, metamorphic rocks, and sedimentary rocks.

And we're going to look at the characteristics of each of these types of rocks now.

So let's check your understanding before we do so.

Which of these is not a type of rock found on earth? Is it A, igneous; B, metamorphic; C, ingenious; or D, sedimentary? Pause the video and have a go at answering this check for understanding.

Well done if you said ingenious, we just established that igneous rocks, metamorphic rocks, and sedimentary rocks are the three types of rocks found on earth.

You're doing a brilliant job so far everybody.

So under earth's crust, temperatures are so high that rocks are often liquid.

This is called molten rock.

When molten rock solidifies, it creates an igneous rock.

Sofia says, "Molten rock below the surface is called magma.

Volcanoes often bring it to the surface, and when they do, it's called lava." So it's all the same thing.

It's just called a different name when it's below or above the surface.

Now examples of igneous rock include basalt, obsidian, and granite, and you can see images of those on the screen there.

Now igneous rock can be described as intrusive and extrusive.

Intrusive igneous rock is formed by molten rock that has cooled slowly deep underground and granite is an example.

Extrusive igneous rock is formed by molten rock on the surface that has cooled quickly.

So basalt is an example.

So intrusive is when it's formed deep underground in the earth, and extrusive is when it's formed on the surface and is cooled quickly and it's outside the earth.

Now, the Giant's Causeway in Northern Ireland is an example of a UK landscape made of the igneous rock, basalt.

And Dartmore, in Devon, has granite tors.

So it's also an example of a UK landscape that contains igneous rock.

So we can see igneous rock on the surface in very different places.

Lucas said, "Did you know? Granite from Scotland is used to make curling stones as when it's polished, it moves really smoothly across the ice." No, I didn't know that, Lucas.

Thank you for sharing.

And Alex says, "Interesting.

Obsidian is also used for decorative figures because its shiny finish makes the decorations interesting to look at." Thank you, Alex.

And Alex has mentioned another type of igneous rock there, obsidian.

So we can see that igneous rocks have lots of different uses.

Thank you, Alex.

Let's check your understanding.

So which of the below best describes how igneous rock is formed? Is it A, through compaction of sediment over time; B, through heat and pressure transforming an existing rock; or C, through the cooling and solidification of magma or lava? Pause the video and have a go at completing this question.

Well done if you said C, through the cooling and solidification of magma or larva.

Well done, geographers.

Now our next type of rock, sedimentary rock, are formed when sediment is carried and deposited through natural processes such as weathering, erosion, and transportation.

This sediment is then compressed in layers by wind, water, or ice.

So the grains and sedimentary rock are arranged in layers.

Usually, the oldest layers are at the bottom and the youngest layers are at the top.

Sometimes tectonic movement can cause rearrangement of the sedimentary layers, but we do often see these layers constructed like they are in that photo.

Now, examples of sedimentary rock include chalk, limestone, and sandstone, and we can see those on the screen there.

Sedimentary rocks are formed in stages.

So firstly, eroded sediment is transported through water, then sediment is deposited to form layers, then those layers are compacted before salt crystals cement the layers into rocks.

So we can see we need to have that loose sediment being deposited to form layers, and then over time it compacts.

So the first layers to be deposited are at the bottom, making those the oldest.

So that's how our sedimentary rock forms in stages.

Fossils are often found in sedimentary rocks as the sediment has formed around the plants and animals.

So when those layers build up around different plants and animals, they are preserved and create fossils over time.

So that's why we often find fossils in sedimentary rock.

Now, sedimentary rocks can be seen in different places around the UK such as in the Yorkshire Dales.

The image on the screen there shows a feature called a limestone pavement.

But we can also see sedimentary features such as these sandstone cliffs in Bridport in Dorset.

So we can see that sedimentary rock features again in very different places around the UK.

Now, sedimentary rocks such as sandstone and limestone are easy to shape and they're therefore used as building stones.

Limestone in particular can last for many years without being worn away, which makes it really useful for building stones.

Let's check your understanding and I'd like you to put these stages of sedimentary rock formation into order.

So you have A, cementation; B, deposition; C, compaction; and D, erosion and transportation.

Pause the video and have a go at putting them into the correct order to show sedimentary rock formation.

Well done for giving that a go, geographers.

Let's check your answer.

So firstly, we have the erosion and transportation, then our sediment is deposited, so B, deposition comes second, followed by C, compaction, and then A, cementation.

Good work, geographers.

I'm sure you got that spot on.

Which of these is not a type of sedimentary rock? Pause the video and have a go at completing this question.

Well done if you said obsidian.

We know that A, limestone and C, sandstone are examples of sedimentary rock, but obsidian was Alex's example of metamorphic rock from earlier in today's lesson.

Well done if you've got that spot on.

Now, our last type of rock that we find in the UK are metamorphic rocks.

And metamorphic rocks are formed when igneous or sedimentary rocks change due to heat or pressure.

Sometimes one metamorphic rock can change into another metamorphic rock.

So we can see in the diagram here we have our molten magma at the bottom, then we have our metamorphic rock in the centre, and then on top of that we have massive pressure due to the weight of overlying rock players.

So we have that pressure coming from the top, but we have that heat coming from the molten magma at the bottom and that has created the metamorphic rock in the centre.

Now there are three stages in the formation of metamorphic rocks.

Firstly, movements of earth's crust cause rocks to be deeply buried or compressed.

Then this causes rocks to be heated and puts them under pressure.

And lastly, the rocks don't melt, but their minerals are changed and they form metamorphic rocks.

So we can see that there are three key stages in the formation of metamorphic rocks.

Now we've got some examples of metamorphic rock.

Marble, slate, and our last one, which looks to have a funny name, but Andeep says there the last one is pronounced nice.

So they are our three examples of metamorphic rocks.

Now, around 22,000 tonnes of marble will use to build the Parthenon, an important temple in Athens in ancient Greece.

And secondly, slate is useful for roof tiles because it can be split into separate flat sheets and it's in permeable, which means it's waterproof.

Now slate is made from shale.

So again, another example there of a metamorphic rock.

Let's check your understanding.

So which of the following factors cause metamorphic rocks to form? Is it A, heat; B, sediment; C, pressure; or D compaction? Pause the video and have a go at answering this question.

Well done If you said A, heat and C, pressure.

We know both of those forces act to create our metamorphic rocks.

Well done, geographers.

So we're now gonna practise what you've learned so far.

So for this practise task, I'd like you to complete the table, giving details on the different types of rocks.

So for igneous rocks, you need to comment on how it forms and provide examples.

For sedimentary, you just need to provide examples because how it forms is already given to you.

And for metamorphic, you need to comment on how it forms, but those examples are there that have already been provided.

Pause the video and have a go at completing this practise task.

Well done, geographers.

Let's check your answers.

So for igneous rocks, for how it forms, we could have said, "When molten rock solidifies, it creates an igneous rock.

Examples may include basalt, obsidian, granite." Metamorphic rocks, how they form, so metamorphic rocks are formed when igneous or sedimentary rocks change due to heat or pressure.

And then examples of sedimentary rock could include chalk, limestone, and sandstone.

Well done if you've got that spot on, but well done if you also included more details such as the difference between extrusive and intrusive igneous rocks.

I'm sure you've done fantastically.

You are doing so fantastically today, geographers.

And we're now ready to move on to our second learning cycle, understanding the rock cycle.

So rocks do not stay the same forever.

Different processes cause them to change.

The rock cycle is a continuous process that forms, alters, and reforms rocks.

So we can see on the diagram here we have our igneous rocks, our metamorphic rocks, and our sedimentary rocks, and we also have sections for sediment and magma.

And we want to find out how these are all connected.

Now there are different processes that cause rocks to change.

If we take a look at an igneous rock, we know if it's heated, it forms magma.

Likewise, if we have a metamorphic rock and heat it, it also forms magma.

If we take that magma though and cool it down, we end up with an igneous rock.

If we take a look at igneous rocks and apply heat and pressure, we end up with metamorphic rocks.

But the same applies to sedimentary.

If we apply that heat and pressure, we end up with metamorphic rocks.

If we erode and weather those metamorphic rocks, we end up with sediment.

If we take our sedimentary rocks and our igneous rocks and erode them or weather them, we also end up with sediment.

But when that sediment is compacted or cemented, we end up with sedimentary rocks.

So if we take a look at this rock cycle here, we can see that all of those different types of rock are connected through different processes.

So there are clearly different processes that cause rocks to change.

So true or false, rocks stay the same over time.

Pause the video and have a go at answering this question.

Well done if you said false.

Rocks are vulnerable to different processes and are therefore cycled through the rock cycle, and we saw that when different processes affect those rocks, they can transform into different types of rocks.

So absolutely, rocks do not stay the same over time.

Now, rocks beneath the earth's crust melt due to high pressure and temperature forming magma.

When this reaches the surface, it is called lava, and you can see some on the screen there.

Now, magma and lava then cool and solidify to form igneous rocks.

Now, igneous, sedimentary, and metamorphic rocks are all vulnerable to weathering.

Weathering is the process of being worn down due to exposure to the atmosphere.

And on the screen, you can see three images representing three different types of weathering.

Physical, biological, and chemical.

Now, physical weathering also called mechanical weathering is where rocks break apart due to natural forces without changing their chemical composition.

For example, this could be freeze-thaw weathering where water enters cracks in rocks, freezes, expands, and then breaks rock apart, or exfoliation where rocks heat up in the day and then cool down at night causing them to crack and peel.

Our next example is biological weathering, and this is caused by plants, animals, and microbes breaking down rocks.

Examples can include plant roots growing into cracks, making them wider, or animals like burrowing rabbits digging into the ground and breaking apart those rocks.

And then finally, we have chemical weathering, which is where rocks are broken down due to chemical reactions often involving water or gases.

Examples could be when acid rain caused by pollution react with rocks like limestone and dissolves them or oxidation so rusting when oxygen reacts with minerals in rocks and weakening them.

Each type of weathering plays a role in shaping landscapes all across the UK and the world.

Natural forces like wind, water, and ice can erode rocks.

Erosion is the process of the earth's surface such as rock or soil being worn away.

Now on the screen we can see some examples of some landscapes carved out by erosion, and there are four different types of erosion that could have happened here.

So it could include hydraulic action where the force of the water traps air and water in cracks to wear away those rocks.

It could have been abrasion where rocks scrape against the surface, carving out a landscape or attrition where rocks bash into one another, becoming smaller and rounder.

Or it could have been solution where minerals are dissolved into the water and therefore that erodes different landscapes.

So there are different types of erosion that could have carved out these landscapes on the screen.

Now, eroded material is then deposited in different places before being compacted and cemented together, forming our sedimentary rocks.

And when rocks are heated or pressure is applied, they transform into metamorphic rocks.

So if we take a look at all of those processes in more detail, we can see how we are moving our way round the rock cycle.

Metamorphic rocks may melt again, forming magma, and the cycle continues.

Let's check your understanding.

So which of these is not a process in the rock cycle? Is it A, erosion; B, weathering; C, heating and cooling; or D, condensation? Pause the video and have a go at answering this question.

Well done, geographers, if you said condensation.

We've seen through our explanation that erosion, weathering, heating, and cooling are all processes that exist within the rock cycle.

Good work.

So we are now going to check what we've learned so far and practise this in our next practise task.

And there's two parts to this.

So I'd like you for part one to complete the gaps.

If a volcano erupted and ejected lava, it would harden into blank.

However, due to blank and weathering, this breaks down into small particles.

These small particles are then compressed time to become blank rock.

This is buried deep in the earth's surface and is exposed into intense heat and pressure, transforming it into a blank rock.

If the metamorphic rock is heated enough, it will melt into blank, starting the whole process again.

And at the bottom of the screen, you've got words to use such as erosion, igneous rock, metamorphic, sedimentary, and magma.

So that's part one.

And then for part two, I'd like you to complete the diagram of the rock cycle by adding on the processes.

So you'll have to think about everything we've learned in this second learning cycle.

Pause the video and have a go at both parts to this practise task.

Well done for giving that a really good go, geographers.

Let's check your answers.

So for part one, we needed to complete the gaps.

If a volcano erupted and ejected lava, it would harden into igneous rock.

However, due to erosion and weathering, this breaks down into small particles.

These small particles are then compressed over time to become sedimentary rock.

This is buried deep in the earth's surface and is exposed to intense heat and pressure, transforming it into a metamorphic rock.

If the metamorphic rock is heated enough, it will melt into magma, starting the whole process again.

Good work, team.

And then for part two, we needed to complete the diagram of the rock cycle by adding on the processes.

So from magma we add cooling to make igneous rock, and if we heat that igneous rock, we form magma again.

If we apply heat and pressure to igneous rock, we end up with metamorphic.

And then if we heat that metamorphic rock, we end up with magma.

If we erode and weather the metamorphic rock, we end up with sediment.

Likewise, if we erode the igneous rock and weather that too, end with sedimentary rock.

If we compact or cement the sediment, we end up with sedimentary rock.

And if we apply heat and pressure to sedimentary rock, we end up with metamorphic rock.

So hopefully, you've got those all spot on.

Well done.

Geographers, you've been fantastic today.

You've worked really hard and achieved lots of fantastic things.

So let's summarise what we've learned today.

So there are three types of rock.

Igneous, sedimentary, and metamorphic.

Igneous rocks are volcanic rocks and examples include basalt, obsidian, and granite.

Sedimentary rocks are formed from sediments and examples include sandstone, limestone, and chalk.

And metamorphic rocks are formed through heat and pressure and examples include slate, gneiss, and marble.

You've been brilliant today, geographers, and I'm really proud of everything you've achieved.

I'm looking forward to seeing you in our next lesson.