Hello, my name's Mrs. Niven, and today we're going to be talking about the formation of sedimentary rocks, as part of our unit on the Carbon Cycle and Climate Change.

Now, you will have some experience of what we talk about in today's lesson from some of your previous learning, but what we do in today's lesson will help us to better understand and answer that big question of how we can explain the changes that occur between the air, the land, and the oceans.

By the end of today's lesson, you should hopefully feel more comfortable being able to describe how sedimentary rock is formed, but also suggest information that may be obtained from examining its layers a little bit more closely.

Throughout the lesson, I will be referring to some keywords, and these include sediment, deposition, compaction, cementation, and strata.

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, or perhaps jot them down 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 halves.

First, we'll look at how sedimentary rock forms, and then we'll look at how we might examine those sedimentary layers a little bit more closely.

So let's get started by looking at how sedimentary rock forms. Our story begins by reminding ourselves that over many years, rock on Earth's surface is weathered in a variety of different processes, and those could be biological, chemical, or physical processes.

Now, those weakened or broken pieces of rock can be eroded or transported to a new location in many different ways, and that includes things like using the wind, by glaciers, or even by rivers or streams. One thing to keep in mind though is that this erosion does not happen consistently, okay? Faster flowing wind or water is going to be able to transport not only more rock fragments, but also larger rock fragments from the source of that rock in the first place, than say slower flowing wind or water.

Moreover, smaller or more lightweight rock fragments are going to be transported far more easily in slower flowing wind or water.

So one could predict then that when you see faster flowing water, not only do we have possibly many rock fragments being eroded, but also larger rock fragments, and that those fragments are being carried a further distance.

Whereas if we saw slower flowing wind or water, then there's probably fewer rock fragments in that medium, and that the ones that are being carried are probably smaller and they're not going as far.

Let's stop here for a quick check, which pictures can move bits of rock or sand to another place? Well done if you said all of them.

I know that we mentioned water, ice, and wind earlier, but gravity is also another way in which rock or sand could be eroded.

So well done if you manage to get that correct.

Guys, great start.

So we know then that there are many ways in which rock fragments can be moved from one place to another, but what we also need to remember is that wind will slow down when it hits an obstruction, and those could include things like trees, mountains, or buildings.

Likewise, water tends to slow down when it flows across flatter land, and sometimes it can stop entirely.

That's one of the reasons we get puddles sometimes.

The water's not able to flow any further.

What happens then is that when that wind and water slows down, the rock fragments that it was carrying tends to be dropped, and rock fragments can also be dropped from other erosive forces like glaciers when they melt.

Now material then that is dropped when that wind or water slows down or the ice melts are known as sediments.

And sediments tend to be small grains then that are composed of many different types of materials.

And these materials can include things like sand, pebbles, mud even, sometimes organic remains, and even salts.

So we've learned then that rocks can be weathered, broken apart, they can be eroded, so moved from one place to another.

And then when these mediums that were carrying these rock fragments slow down or melt, as in the case of the glaciers, they drop that material, that material being the sediments.

Now this entire process then of dropping sediments is known as deposition, and we can see that in pictures like this where that sediment starts to collect in places where it's been deposited.

So we've got here a river, we can see where those sediments have started to collect in places, and we can also see in this picture of a desert where some of that sand has been eroded and then deposited elsewhere as the wind slows down, as we start to get developed these sand dunes.

Now over time then this deposition creates layers of different sediments, and they can build up on top of each other, and the weight then of those upper layers exerts some pressure then on the layers below.

So a little bit like being at the bottom of a rugby pile for instance.

Now this increasing pressure then causes sediments to undergo a process of compaction.

Now, what compaction does then is it pushes those sediment grains closer together, as well as squeezing out some groundwater that may exist between those grains.

So if we were to zoom in on one of my sediment layers, I can see here, then I've got my sediment grains and the groundwater.

And as that pressure increases, as more and more sediments are deposited above this layer, then compaction occurs, and we can see then that those grains of the sediment have gotten closer together and some groundwater has been pushed out of that area.

Let's stop here for another quick check.

Which sediment layer is experiencing the least compaction? And I'd like to challenge you to explain why.

So I'm looking for a because clause to explain your choice.

Well done if you chose letter A.

Now, did you get the correct reasoning though? I would've said, "Because letter A represents the layer that has the fewest layers above it, and therefore it has the least amount of pressure being exerted on it.

And therefore it is experiencing the lowest amount of compaction." So very well done if you chose the correct layer, and incredibly well done if you manage to explain correctly why that was the correct answer.

Well done guys.

Now what we need to remember is that groundwater that's moving between all these different sediment grains can actually deposit natural minerals.

So minerals tend to be crystal like substances, like quartz, or calcite, and they're being deposited in the pores, or those spaces between the sediment grains.

Now, the increased pressure and temperature that takes place because of compaction provides them those conditions for mineral crystals to now form inside the pores between those sediment grains.

These mineral crystals then as they start to grow, act like glue, sticking those sediment grains together.

And this entire process then is known as cementation, where those sediment grains are cemented or glued together by those mineral crystals.

And at this point then we now have a sedimentary rock that has been formed, and we can see here a cross section of an actual sedimentary rock, and we can clearly see then those sedimentary grains, and those mineral crystals that are glueing or sticking together those individual grains.

Now, because there are so many steps to the formation of a sedimentary rock, this process can take millions of years to occur.

If you think about it, we have to first weather and erode existing rocks.

Then those sediments that are formed need to be deposited, and many layers of sediment need to be deposited in order to compact other sediment layers.

And then we need to wait for those mineral crystals to grow, and cement all those different sediment grains together.

So it's an incredibly long process, and because of that takes millions of years.

In fact, then the oldest sedimentary rock that has been found in the UK was formed from sand deposits that were deposited 1000 million years ago.

It's in Scotland if you ever get a chance to have a look, but yes, very, very long time to form these rocks.

Let's stop for another quick check.

So we know that sedimentary rock takes millions of years to form, which mixtures listed below do you think I could use to make an artificial rock? Well done if you chose C, D, and E.

The key ingredients here is that we have water and we have cement.

So those two are very key so that we can move that cement, which is acting as our mineral crystals, and the water is used to move those cement crystals between our sediment grains, which is represented by the sand and the grit.

So very well done if you manage to get those correct.

Okay, let's take a moment to just remind ourselves of some key facts.

We know that water flows downhill due to gravity.

It's one of the reasons we can see waterfalls.

We also know that sedimentary rocks, like limestone tend to have pores of spaces between those sediment grains.

Well, groundwater flowing through the pores of limestone is able to dissolve that mineral, that glue in the rock, and move that mineral, that calcium carbonate, or calcite mineral to another location.

So we can dissolve the glue between the sediment grains and move that mineral to a new location.

Now in some locations then those dissolved minerals are actually deposited above ground.

If you've ever been to Turkey, you may have been lucky enough to go to this UNESCO World Heritage site.

And here the calcite minerals, or the calcium carbonate glue that was holding the sediment grains together, are being brought to the surface by a thermal spring water.

And then as that water overflows from the basins, it deposits those minerals.

It deposits that calcite.

And it looks a little bit like icicles, but really all it is is that calcium carbonate mineral being deposited and sticking itself, glueing to the sides of that basin.

Other times the minerals are deposited underground.

Now, if that mineral rich groundwater reaches a cave, that calcium carbonate or calcite mineral is deposited as the water drips from the ceiling, and this then results in the formation of stalactites and stalagmites.

Now, I always get these mixed up, but the stalactites are what form from the ceiling, they hang like tights from the ceiling, and the stalagmites then form from the floor, depending on how much mineral is within that water as it drips from the ceiling.

Let's stop here for one more quick check.

True or false, the size of stalactites get smaller over time.

Well done if you chose false, but which of these statements best supports that answer? Well done if you chose A, minerals from rock dissolve in water and then can be transported, or deposited elsewhere.

Well done if you got this correct.

Great job, guys.

Time now for the first task in today's lesson.

For this first part, what I'd like you to do is match each word to the best description.

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

Okay, let's see how you got on.

So a sediment, if you remember, is the material that's deposited by water, wind or ice.

While compaction pushes sediment grains closer together or compresses them, or compacts them together.

Deposition then is the process of dropping sediment.

So deposition is dropping.

Cementation then is those mineral crystals glueing grains together, so cementing those grains together.

And a mineral then is the crystal-like substance that makes up rocks, and a good example of this is quartz.

Very well done if you manage to match those correctly, guys.

Now the second task is a little bit trickier.

We know that sedimentary rock forms in layers.

What I'd like you to do is to order the appropriate statements below to describe how sedimentary rock forms, and some of these statements are not needed.

If you are struggling to remember some of the different processes, it might help for you to go back to those keywords that you matched up from part one.

I would highly recommend that you talk over your ideas with the people nearest you, but definitely pause the video then, and come back when you're ready to check your work.

Okay, let's see how you got on.

Now, I did give you the first step, which was that a layer of sediment collects in one place.

The second step then would be that over time the sediment is buried under other layers of sediment.

At this point then the sediment grains start to get compacted under that increasing huge amount of pressure, and then groundwater flows through the sediment.

And when it does that, the minerals from the groundwater is able to form crystals.

And those mineral crystals then cement those sediment grains together.

Those are the only statements that you should have needed in order to describe how the sedimentary rock forms. The other four were not needed.

So very well done if you manage firstly to select the correct statements to order, and very well done if you put them in the correct order.

Great job, guys.

For this last part, I'd like you to help Alex.

He's written some statements describing sedimentary rocks, but each one of them contains an error.

So what I'd like you to do is identify and correct each error in Alex's statements below.

Pause the video and come back when you're ready to check your answers.

Let's see how you got on.

So for part A then Alex said that "Sedimentary rocks are formed from many large grains stuck together," but really it should be small grains.

Sedimentary rocks are formed from small grains that are stuck together.

In B, Alex had said, "Sedimentary rocks often contain no pores or gaps between the grains," but actually sedimentary rocks do contain pores between those grains.

I would've simply removed the word no.

And for C, Alex said that "Sedimentary rocks can take only a few years to form," but you may remember that we said there's quite a few steps that's part of this process, and because of it, it actually takes millions of years to form a sedimentary rock.

So very well done if you managed to identify the error that Alex made.

And incredibly well done, if you managed to correct it.

Fantastic start to this lesson, guys.

I'm really impressed with your work.

Now that we're feeling a little more comfortable discussing how sedimentary rocks form, let's move on to look at information that scientists can get when they examine those sediment layers a little more closely.

Now, we learned earlier that all sedimentary rocks are formed by the same process of this weathering, erosion, deposition, compaction, and cementation.

But different sediments form different sedimentary rocks.

For instance, sand as a sediment moves to make sandstone.

The gravel as a sediment forms a sedimentary rock known as conglomerate.

And clay as a sediment will make the sedimentary rock known as shale.

Moreover, some sedimentary rocks are formed from sediments that are the remains of living organisms. For instance, chalk is formed from microscopic plankton remains, whereas limestone is made from the remains of larger shellfish.

Let's stop for a quick check.

Which of these is not a sedimentary rock? Well done, if you said A.

Clay is the sediment that forms the sedimentary rock known as shales.

Very well done if you got that correct.

So we know that sedimentary rocks are formed when sediments are deposited in layers.

Now, when scientists refer to then one sediment layer, what they're talking about is a stratum.

If we are referring to many layers within our sedimentary rock, we are referring to those as strata.

So stratum is one and strata is many.

Another quick check then.

How many strata are shown in this image? Well done if you said five.

We do need to include that top layer of soil.

That is still a layer within our structure here.

So very well done if you managed to choose five.

Great job guys.

Now, you might be wondering why I'm making a distinction between stratum versus strata.

And the reason is because each stratum in at the strata of a sedimentary rock helps us to build a relative timescale, because upper strata, many layers, were deposited after or later than the lower strata, or lower layers of sediment.

So if we look at this hole that's been dug, at an excavation, we can say then the upper stratum is a recent deposition, and therefore anything that's found in that layer is from the recent past.

Whereas the lower stratum represents earlier deposition, and therefore anything found in that layer would be from the distant past.

So scientists will study strata to gain information about the past because objects that are found in each stratum help build an understanding about organisms living at that time.

Some scientists that would study strata then include biologists, geologists, and archaeologists.

Let's stop for another quick check.

Which stratum was deposited first and how can you tell? Well done if you chose D.

Now D is the correct answer because it is the lowest labelled stratum.

Remember that the lower down that stratum is found the earlier it was deposited.

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

Now, by examining strata a little bit more closely, scientists are able to discover clues to past environments.

For instance, cross beds form due to shifts in the way that sediments were deposited.

Now, this could have been caused by a change in wind direction, which results then in the change of the direction that those sediments were deposited.

And you can see that in the picture here with the different arrows showing where those deposited layers have laying then in our sedimentary rock.

Now, this particular strata composition then could indicate perhaps an ancient desert that ones once here.

In other places, ripples may be found in strata, and that could suggest that a current was present when that particular sediment was deposited.

And those details then could indicate perhaps an ancient river, a stream, or even a seabed was once located where this strata was found.

We come now then to the last task in today's lesson.

What I'd like you to do, please, is to use the table below and the statements on the next slide to label which sedimentary rock is found in each stratum on the diagram.

Now, you may wish to pause the video here to make a quick note of the table before moving on to the next slide.

You'll need to now read these statements carefully and compare the information against your table of sediments and sedimentary rock to decide which type of rock was formed in each stratum of our diagram.

I'm going to recommend that you pause the video here, so that you can read these statements and refer back to them multiple times if needed, and perhaps discuss your ideas with the people nearest you before you come back to check your answers.

Okay, let's see how you got on.

So layer A was the chalk or that was formed from microscopic plankton.

B was the shale formed from the sediment of clay.

C was limestone 'cause it was formed from shellfish remains.

D is sandstone formed from sand sediment.

And then E was our conglomerate formed from the gravel sediment.

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

A common error here is to write down the sediment that was laid down, but remember, we were asking for what sedimentary rock was actually formed.

So it's very important that we are clear that the sediment name does not represent the sedimentary rock name.

But very, very well done.

I'm really impressed with how you guys got on in today's lesson so far.

Brilliant, brilliant work.

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

Well, we learned that sediments are deposited when wind or waterways slow down or when glaciers melt.

And that layers of sediment form over many years, and that can lead to compaction or this pressing together of these different layers of sediments.

And then sedimentary rock forms when sediment is buried, compressed, and then crucially, those minerals from the groundwater grow crystals, which then cement those sedimentary grains together.

And it's able to do that because water in nature always contains minerals.

Then when these rocks are formed, strata can be used to create a relative timeline to provide clues to the environment, and the history of when those sediments were deposited.

So it gives scientists a lot of information to learn about Earth's past.

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

I certainly had a good time learning with you.

And I hope to see you again soon.

Bye for now.

(computer mouse clicks).