Hello, my name's Mrs. Niven.

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

Now you may have some experience of what we talk about in today's lesson from your previous learning.

But what we do today will help us to better answer that question of how can we explain changes on Earth's air, oceans, and land? So by the end of today's lesson, you should hopefully feel more comfortable being able to describe how rock can be changed deep underground.

Throughout the lesson, I'll be referring to some keywords.

And these include pressure, metamorphic, and aligned.

Now the definitions for these keywords are given on the next slide in sentence form.

And you may wish to pause the video here so you can read through them, or perhaps even make a note of them to refer back to later on in this lesson, or later on in your learning.

Now today's lesson is broken into two parts.

We'll look at describing underground conditions before moving on to describe how they impact the formation of different metamorphic rocks.

So let's get started at describing what we mean by underground conditions.

Now you may be familiar with this idea of pressure and that it's the effect of a force acting over an area.

And that pressure can increase or decrease depending on how much force is applied.

You'll be familiar with this if you've ever taken care of a bicycle.

For instance, a flat bicycle tyre is the result of a small force of air within that tyre causing low pressure, and that ends up with a flat tyre.

You can correct that though by inflating that bicycle tyre and what that causes then is a larger force within that tyre and causing a higher pressure.

So small force is a low pressure and a large force equals a higher pressure.

Now, changes in pressure can also occur on larger scales like in the atmosphere where pressure is lower at higher altitudes.

So if we consider sea level is experiencing a pressure of one atmosphere.

If you go into the mountains, and let's say the highest mountain that we can come to into the Rockies about 4,400 metres.

You would experience pressure that is 0.

57 atmospheres.

And if we go higher still, for instance, in an aeroplane, these travel at about 9,100 metres, that's about 30,000 feet above sea level, and the pressure here reduces even further to not 0.

29 atmospheres.

So as we go further away from Earth's surface, the pressure is reduced.

Similarly, pressure changes as you go below sea level.

For instance, if you had some scuba gear, you might be able to travel to a depth of 60 metres, and here you would be experiencing a pressure of six atmospheres on you.

And to go below this depth, you would actually need specialist equipment.

Now some animals are actually adapted to travel below this depth.

For instance, elephant seals have dived as low as 1,500 metres below sea level.

And here they're experiencing 150 atmospheres worth of pressure.

And curvier beaked whales have been able to dive double that and experience 300 atmospheres worth of pressure.

So as we go below sea level, we are experiencing an increase in pressure.

Let's stop here for a quick check.

What is the effect of a force acting on an area known as? Well done if you said B, it is pressure.

Very well done, guys.

What a great start.

So keep it up.

What all this means then is that the more layers applying force on an object, the more pressure that object experiences.

So those objects that are near the Earth's surface would experience a relatively low pressure while objects that are further underground would experience a higher relative pressure.

Now, if we expand that even further to talk about the entire structure of Earth.

We can say that pressure then is increasing as we travel from Earth's crust to its core.

And that means then that rock that's deep underground.

So we're talking the lower crust and the upper mantle is under an extreme amount of pressure.

Let's up for another quick check.

True or false? Pressure decreases towards Earth's crust.

Well done if you said true.

But which of these statements best justifies that answer? Well done if you said A, pressure is increasing towards Earth's core, which mean pressure decreases as you travel towards Earth's crust.

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

Great job.

That was a tricky one.

Now we're talking about underground conditions here.

So we know that rocks under Earth's surface is under a lot of pressure, but we need to remember as well that there are radioactive processes taking place in Earth's inner core that generate energy, and that this energy then is transferred through Earth's layers.

So while rocks underground will experience some form of temperature and pressure, not all of those rocks exist under the same conditions of temperature and pressure.

Those areas that are near to and round different tectonic plate boundaries might experience extreme pressures and temperatures.

For instance, where one plate is sliding under another, it might experience extreme pressure from that deep burial underground by having more layers of rock above it.

Also rock that exists near to melted rock known as magma might also experience extreme temperatures as well.

Okay, time for our first task.

What I'd like you to do is to put the letters of each object into order of those experiencing the lowest pressure to the highest pressure.

Now, you may wish to pause the videos so that you can discuss your ideas with the people nearest you and then come back when you're ready to check your answers.

Okay, let's see how you got on.

Now, in order to answer this, we needed to remember that as you travel above C level, pressure decreases, and below C level, pressure increases.

So your final answers then should be A, C, D, B, and then finally E.

So well done if you manage to get those correct, guys.

Great job.

For this next part then, please use an appropriate word from the box provided to complete each sentence.

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

Let's see how you got on.

And what I'd ask you to do is as you are checking your work, make sure you tick these words if you've got them correct, fix them if you got them wrong because this creates a very nice summary of what we've just talked about and definitely fill in those blanks if you left them blank 'cause you weren't sure.

So to read these out then in their correct form, your sentences should read as thus.

Pressure increases towards Earth's core.

Some rocks in Earth's crust experience extreme pressure because there are so many layers of rock piled on top of them.

And some rocks in Earth's crust experience extreme temperatures because they are found near to melted rock.

So very well done if you got those three correct.

Great job, guys.

Now that we're feeling more comfortable talking about and understanding where these underground conditions come from and develop.

Let's look at how they impact then on the formation of metamorphic rocks.

Now you might remember that rocks are composed of minerals and that minerals have a very distinctive and definite crystalline or crystal-like structure because of the way that the atoms are arranged in a regular pattern.

But minerals also have a very definite chemical composition.

Now these compositions and their crystal structures combined to give minerals and then the rocks that they make up their properties, including the rock's texture, its hardness, its colour, and its lustre.

Now if we break apart this word metamorphic, we can understand a little bit more about what it's referring to.

For instance, meta means to change and morph means to form.

So metamorphic is effectively an adjective that's used to describe objects or materials that have changed their form or their appearance, and you'll have seen this before.

For instance, tadpoles undergo metamorphism as they change from a tadpole into a frog.

The same thing can be said of caterpillars that undergo metamorphism to change from a caterpillar into a butterfly.

So changes in temperature and pressure can actually cause rocks to undergo metamorphosis, change of their formal appearance as well.

Now these changes in rocks occur because very high pressures and temperatures at tectonic plate boundaries can cause minerals to be altered or changed, and over millions of years then these large crystals could grow in solid rock.

And it's these alterations that form metamorphic rock.

Let's stop here for a quick check.

Granite is an example of an igneous rock and gneiss is a metamorphic rock.

Which of the following statements is true about granite changing into gneiss? Now, you may wish to pause the video here so you can discuss your ideas with those around you and then come back when you're ready to check your answer.

Well done if you chose B.

It can be hot enough to granite to change into gneiss at the edge of a tectonic plate.

That's where the conditions might be extreme enough to cause that metamorphosis, that changing or alteration of the minerals within granite to form gneiss.

Those conditions are not consistent deep underground everywhere.

They're more likely to occur at the edge of a tectonic plate.

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

It was a tricky one.

It's a great job, guys.

Keep it up.

Let's try another quick check then, what two conditions can cause rocks to undergo metamorphosis? Well done if you said B and D.

It's those extreme temperatures and pressures that cause rocks to undergo metamorphosis.

Well done if you got those two correct, guys.

Great job.

Now the thing about metamorphic rocks is that they form as a result of sustained extreme pressure and or extreme temperatures.

And what that causes then is the mineral structure or the composition of the original rock to change without the rock actually melting into magma or molten rock.

So the original rock then could be sedimentary rock, it could be igneous rock, or it could be other metamorphic rock that's undergoing these sustained experiences of extreme temperature and pressure.

So ultimately, the metamorphic rock that forms depends on the amount of pressure or temperature that that original rock is experiencing and for how long it's under those conditions.

So the longer the original rock is experiencing those temperatures and pressures, it will undergo increasing metamorphism, increasing changes and alterations.

So let's look at an example.

Ultimately, what that means then is different temperature and pressure combinations can cause different metamorphic rocks to form because of these different conditions.

So if we say that we're starting with this original sedimentary rock of shale.

As it starts to undergo increasing temperatures and pressures, it might change then into this metamorphic rock of slate, which if this as well undergoes more temperature and pressure that could change into schist, which could then change into gneiss before eventually reaching a temperature and pressure that are the conditions for it to then change into magma.

So the slate, the schist, and the gneiss are all examples of different metamorphic rocks that form as a result of these changing extreme temperatures and extreme pressures without melting into molten rock.

Let's stop for another quick check.

True or false? All metamorphic rocks form under the same conditions.

Well done if you said false, but which of these statements best justifies that answer? Well done if you said A, metamorphic rocks continually change with those continually changing conditions of temperature and pressure.

Very well done, guys.

Great job.

Now, one of the features that develops then in metamorphic rocks is that those crystalline or crystal-like minerals become aligned.

So the structure of the minerals is altered through this re-crystallizing while the mineral composition is completely unchanged.

So if we look at an example, for instance, of limestone as a sedimentary rock.

As it undergoes these different conditions of pressure and temperature, it can develop into marble, which is the metamorphic rock.

And what we can see here is these aligned or in a straight line minerals that we have.

So the same minerals are here, they're just arranged differently in these new crystal structures.

Now these aligned minerals then form layers which give metamorphic rocks properties that are widely useful.

For instance, they provide these lovely effects that can be useful in decoration.

These lined minerals make metamorphic rocks quite useful for sculptures.

And because we have these layers, you can also use metamorphic rocks quite usefully for worktops or even roofing tiles.

Now the mineral composition themselves are stable on a very specific range of conditions like temperature and pressure.

So if those temperature and pressure conditions change outside of that stable range, the minerals themselves might change into different more stable minerals.

So the composition might slightly alter and these different minerals then mean that a different metamorphic rock has formed.

Let's move on now to the last task in today's lesson.

For this first part, I'd like you to please put appropriate statements from below into an order that describes how gneiss, a metamorphic rock is formed.

Now beware, though, because some statements may not be used.

You may wish to pause the video here so you can discuss your ideas with the people nearest you, and then come back when you're ready to check your work.

Okay, let's see how you got on.

So if I were you, I would've started with the very first one being that solid rock at the edge of a tectonic plate could become very hot.

And as that happens, crystals could grow in the solid rock.

And those crystals tend to be quite large, and they would normally form in layers.

The two statements you wouldn't use though are that solid rock deep underground melts and becomes magma because remember, metamorphic rocks are changes in rocks that occur before it melts into this molten magma.

So very well done if you chose the correct statements to use, and incredibly well done if you managed to put them in the correct order.

Well done.

Okay, for this next task then we're going to look at how we can model metamorphic rocks forming in a few different ways.

And the first one, we're going to use is toothpicks and two rulers.

So you're gonna take your small toothpicks and simply just hold them slightly above your desk and let them fall, okay? Don't do it too far, or they'll go all over the place.

So just a few inches off your desk and let them drop.

Sketch how that looks then in the box below.

Then what you're going to do is take two rulers on either sides of those sticks and slowly push them together.

And then I'd like you to sketch how the sticks now look in the box below.

So pause the video whilst do you complete that task and we'll come back to check your sketches in a moment.

Okay, everybody's sketches will be slightly different, but what we'll notice is that in the first box, it does look quite random, whereas in the second box, you can see that they start to come close together and they're aligned a little bit more.

For this second modelling task then we're going to use plasticine and a stirring rod.

So what you want to do is to create a smooth square plasticine a few centimetres thick.

And then you're going to push the end of the stirring rod into the plasticine to create small dots in the surface.

And we're looking at maybe half a centimetres depth maximum, okay? No, we're not massive holes in it, just small dots into it, okay? Once you've done that, draw a sketch of what your plasticine looks like in the first box.

Once you've done that, you're going to take the edges of your plasticine and push them together, and then sketch how the surface looks in the box below.

So pause the video whilst you complete that task and we'll come back to check your sketches in a moment.

Now, as we found with the toothpicks and rulers modelling, everybody's sketches will be slightly different, but you'll notice then on mine, the first one is taking up the whole box and the second one looks slightly different because again, I have pushed the edges of that plasticine together.

And hopefully, you've been able to sketch those as accurately as possible, but very well done for completing that task.

For this next task then I want you to reflect on your sketches that you've created in task B part two.

For this first part, what do you think those rulers are simulating? And then what do you notice has happened to the toothpicks and the dots when the edges were pushed together? Now you may wish to pause the video so you can discuss your ideas with the people nearest you and then come back when you're ready to check your answers.

Okay, let's see how you got on.

Hopefully, what you've noticed then is that the rulers were simulating an increase in pressure.

So we're showing that increase in pressure in our model of metamorphic rock.

So well done if you managed to get that correct.

So what you may have noticed then is that the toothpicks became more aligned, like the crystals and metamorphic rock would become due to that increased pressure.

And that the dots become thinner and flatter, and this is simulating the minerals re-crystallizing and changing into different minerals.

Now, the toothpicks ones I think was probably an easier one to try and identify what's going on here, but the dots was a little bit trickier to explain how that's modelling the metamorphism that takes place in rock.

So very well done if you manage to suggest what that might've been modelling, but very, very well done.

I hope you enjoyed that.

Sometimes it's difficult to play around with the different processes that take place with rocks, and this is kind of a fun little modelling experience.

So I hope you enjoyed that.

We've gone through a lot in today's lesson.

So let's take a moment to summarise what we've learned.

Well, we've learned that when some substances are put under very high pressures and high temperatures, their particles can be pushed together and form crystals.

And that a crystal, all the atoms are arranged in a very regular pattern.

But the temperature and pressure are high enough near to tectonic plate boundaries for large crystals to grow inside solid rock.

And that metamorphic rocks form then under extreme pressures and extreme temperatures altering the structures of those original rocks, and that an aligned crystal structures in those metamorphic rocks give these rocks properties that are quite useful for things like decorations, or being easily separated into sheets.

I had a good time learning with you today.

I hope you had a good time learning with me, and I hope to see you again soon.

Bye for now.