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 gonna 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.

The title for today's lesson is "The Importance of Soil," and this sits within the unit "Rocks, Weathering, and Soil: Why is Geology Important?" Our learning outcome for today's lesson is that I can explain what soil is made of, how it forms, and understand its importance.

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

They are soil, erosion, carbon store, and weathering.

Soil is the loose upper layer of the Earth's surface where plants grow formed of minerals, organic matter, air and water.

Erosion is the process of the Earth's surface, such as rocks or soil being worn away and transported from its original site.

Carbon store is something that absorbs and holds carbon.

And weathering is the process by which Earth's surface is worn down due to exposure to the atmosphere.

So soil, erosion, carbon store and weathering are going to be really useful to us in today's lesson.

This lesson is split into three learning cycles.

Number one, what is soil made of? Number two, how does soil form? And number three, why is soil important? And we're gonna start with learning cycle one now, what is soil made of? Now, soil might just look like a patch of dirt, but it's actually a fascinating and complex mixture that plays a vital role in supporting life on Earth.

Soil is made of four main components: minerals, organic matter, water and air.

Minerals come from rocks that have been broken down over a long period of time by weathering.

Weathering happens when wind, water and temperature changes and chemicals slowly wear down rocks into tiny particles.

These mineral particles give soil its basic structure and help to determine its texture, whether it feels sandy sticky or clay, or even crumbly.

The next part that's really important to soil is organic matter, and this is made up of things that are either alive or were once alive.

It can include dead plants, fallen leaves, animal remains, and waste.

As the material breaks down through a process called decomposition, it becomes dark and rich forming humus.

Humus helps feed plants and improves the soil's ability to hold water and nutrients.

And then we move on to the next key important component, which is water.

Now, soil holds water in the tiny spaces between its particles.

The water is essential because it carries nutrients that plants need to grow.

The amount of water a soil can hold depends on its texture.

Sandy soils drink quickly while clay soils do hold much more water.

And the last really important component is air.

Believe it or not, good soils need lots of air.

Air fills the gap between soil particles and provides oxygen for plant roots and for tiny organisms living in the soil.

Without enough air, plants can't breathe properly and they may really struggle to grow.

So all of these four components are really important when we are looking at what soil is formed of.

So we're gonna check your understanding.

What are the four components that make up soil? Pause the video and have a go at answering this question.

Well done for giving that a really good go.

Let's check your answer.

So you should have minerals, organic matter, water and air.

Well done if you've got those spots on.

You're doing a brilliant job so far.

So there are three main particle sizes in soil: clay, sand, and silt.

Clay particles are the smallest particles as they're smaller than 0.

002 millimetres.

They're so small that often when we see them, they look like one continuous clump, and it's really hard to see the different particles.

We then have our silt particles, which are slightly bigger.

At 0.

05 to 0.

002 millimetres, they're 10 times bigger than clay, and you can start to see those differences in that image.

And lastly, we have our sand particles.

And these are the biggest particles because they're 1000 times bigger than clay, at 2 to 0.

05 millimetres each.

So sand looks different again, and you can see that comparison clearly in that image.

Now, different combinations of soil particles and amount of organic matter create many different types of soil.

Sandy soil is pale and has big gritty particles.

This means that it has lots of small air gaps and water drains through it easily, so it often feels dry.

Next, we have our clay soil, which is usually sticky as it has really small particles.

Water doesn't drain through it easily because there are not many air spaces.

Sam says, "The particles are so small, they look like one continuous clump." Thank you, Sam.

Chalky soil is light brown in colour, and water drains through it really quickly.

And lastly, we've got peat, and this is made from old decayed plants, and it's dark and crumbly.

It's really rich in nutrient, and it stores a lot of carbon.

So let's check your understanding of those different types of soil.

What type of soil is usually sticky and has small particles? Is it A, peat; B, clay; C, sandy; or D, chalky? Pause the video and have a go at answering this question.

Well done if you said B, clay.

Remember that Sam told us it looks like one continuous clump because particles are so small and usually quite sticky.

Well done, geographers.

So we're gonna practise what you've learned so far about what soil is made of.

So for the first part of this practise task, I'd like you to write a statement that corrects Andeep's misconception about soil.

Andeep says, "Soil is just dirt." And for part two, I'd like you to match up the type of soil to its characteristics.

So you've got four options there.

The first one made from old decayed plants, and it's dark and crumbly, rich in nutrients.

The second has lots of air gaps, so water drain through it easily so it often feels dry.

The third light, brown and water drain through it quickly.

And lastly, water doesn't drain through it easily as there are not many air bubbles and it's sticky.

So your four options are chalky, peat, sandy, and clay, and you need to match up the type of soil to its key characteristics.

Pause the video and have a go at completing those two parts to practise Task A.

Well done for giving that a really good go.

I'm sure you've done brilliantly, but let's double check your answers.

So for part one, Andeep incorrectly said, "Soil is just dirt." Now from learning cycle one, we recognise that soil is the loose upper layer of the Earth surface where plants grow, and it's a mixture of minerals, organic matter, water and air.

So it's not just dirt, and we can correct Andeep's misconception.

For part two, we needed to match up the type of soil to its characteristics.

So peat is made up from old decayed plants, and it's dark and crumbly and rich in nutrients.

Sandy soil has lots of air gaps, so water drains through it easily, so it often feels dry.

Chalky soil is light brown, and water drains through it quickly.

And lastly, clay soil is where water doesn't drain through it easily as there are not many air bubbles and it's sticky.

Well done if you've got those all absolutely spot on.

We're now ready to move on to learning cycle number two, how does soil form? So soil formation is a long and slow process.

It is estimated that it can take up to 500 years for just one centimetre of new soil to form.

And it's thought that soil first began to form over 2,000 million years ago.

So it's a really, really long process that's been happening for millions of years.

So let's check your understanding.

How long is it estimated for one centimetre of soil to form? Is it A, 5 million years; B, 2,000 million years; or C, 500 years? Pause the video and have a go at answering that question.

Well done if you said C, 500 years.

That's absolutely spot on.

We know that the first soil started forming 2,000 million years ago, but it can take 500 years for one centimetre of new soil to form.

Well done, geographers.

So soil formation can vary depending on what type of soil is forming.

However, there are several stages that most soils go through on their way to full formation.

Aisha says, "It also depends on factors such as climate.

The warmer and wetter it is, the quicker rocks and organic matter decompose, and therefore quicker soils form." Thank you.

That's really important.

We know that those different factors can help influence the speed in which our soil forms. Thank you, Aisha.

So the first stage of soil formation is weathering.

Now weathering is the process of being worn down by long exposure to the atmosphere.

This causes rocks to be broken down by factors such as rain, ice, wind, and changes in temperature.

There are three different types of weathering.

The first is biological.

Now this is when organisms break down rocks.

As you can see in the image, the tree has grown between that rock, and therefore that's caused it to start breaking down.

Chemical is when a chemical reaction breaks down rocks.

And lastly, you've got physical weathering, which is when changes in temperatures can cause rocks to expand and can contract.

So there are different types of weathering that can cause those rocks to break down.

We then move on to stage two, which is erosion and then transportation.

Now erosion is the process by which the Earth's surface, such as rocks and soil, is worn away and then transported from its original site.

A bit like weathering, there are different types of erosion can impact the Earth's surface.

They include hydraulic action, solution, abrasion, and attrition.

Now in the image on the screen, you can see that we've got a diagram of the different types of erosion, and this is what they'd look like if they were occurring in a river.

Hydraulic action is where air and water is trapped in the cracks of those rocks causing them to break down over time.

Abrasion is where the rocks scrape along the riverbed.

Solution is where the minerals are dissolved in the water.

And attrition is where the rocks are carried by the water, and when they smash together, they can get rounder and smaller and break down.

Now erosion can be caused by wind, water, or ice.

So in this river it's caused by water.

But if we were looking at a glacier, it would be caused by ice.

As I say, wind can also be a driver of erosion.

Then we move on to stage three, which is deposition, which is where transport sediment is dropped in a new place.

So it's picked up, transported, and then dropped in a new place.

And then the final stage is when tiny creatures, like worms and bacteria, mix together the weathered rock with some organic matter.

Over time, leaves fall, and plants and animals die and decompose.

This creates humus, which is a dark and rich material that's full of nutrients.

This mixes with the weathered rock and creates soil.

The whole process continues over time, building up different soil layers as you can see in this image here.

So we have bedrock at the bottom with weathered rock on top of that.

Then you have your subsoil, then your top soil, and then on the top you have your humus, which is really fertile, and that's where our organic matter grows.

So let's check what you've understood from that.

And I'd like you to put the stages of soil formation into order.

So the options are A, deposition; B, erosion and then transportation; C, weathering; and D, mixing with organic matter.

So I'd like you to number them one to four to put them in order.

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

Well done if you started with C, weathering, then you put erosion and transportation as number two, then deposition as three, and then four, mixing with organic matter.

You are doing a brilliant job, geographers.

So we're now gonna practise what we've learned in learning cycle two.

And for task, I'd like you to explain the different processes that are important in the formation of soil in just one paragraph.

Aisha says, "You could include erosion, weathering, decomposition, transportation, and deposition." Pause the video and have a go at competing that practise task.

Well done for giving that a really good go.

Now your answer might look different to mine, but you should have included all those key processes.

So let's check your answer and see what you could have included.

Soil is made over a very long time through different natural processes.

These include erosion, transportation, deposition, and mixing with organic matter.

Weathering is when rocks are broken down into smaller pieces by rain, temperature changes and plants.

There are three types: physical, chemical, and biological weathering.

This is the first step in making soil.

Next comes erosion, which is when rocks are broken down into smaller pieces by things like wind, water, and ice.

This makes tiny bits of rock called sediment.

Then transportation, which is where the sediment is moved from one place to another, occurs.

Rivers, wind, or glaciers can carry the sediment away.

This is followed by deposition when the sediment is dropped off in a new place.

It usually happens when the wind or water slows down and can't carry the sediment anymore.

Finally, the sediment mixes with organic matter, which comes from dead plants and animals.

Creatures like worms and bacteria help mix it all together.

This creates rich soil that can support plant life.

Well done if you could include all of those different processes in that answer.

I'm sure you've done a fantastic job.

We are now ready to move on to learning cycle number three, our final learning cycle, why is soil important? Now soil is important for many different reasons.

It can be important for things like farming, but also important for climate change.

Soil is essential for farming, as it provides nutrients for crops to grow.

The more fertile the soil, the more crops that farmers can grow.

The more crops they grow, the more they can sell and the more money they can make.

This has local scale economic benefits for the farmers because they're able to earn money.

Less soil can make it difficult for crops to grow.

Now, soil also filters the water that we drink.

And having a good supply of food and water can ensure that people get enough nutrients and can stay healthy, which is a social benefit.

Let's check your understanding then.

So true or false, a social benefit of soil is that it creates more income for farmers.

Pause the video and have a think about what you've learned so far in order to help you answer that question.

Well done if you said false.

We know that providing more income is an economic benefit.

So economic is to do with money, and social is to do with things like education and healthcare linked more closely to people.

Now, soil is also the largest carbon sink after the ocean, and it holds more carbon than all terrestrial part life on Earth.

So a carbon sink is something that absorbs carbon and holds it within our Earth and atmosphere.

Now peat holds a large amount of carbon.

This makes soil essential on a global scale, as it helps in the fight against climate change.

This is an environmental benefit.

Now have talked quite a lot about the environmental, economic, and social benefits of soil.

But I want us to think about what we've mentioned in regards to scale.

So we're gonna check what you've understood from that, and I would like you to complete the sentences by adding the correct scale to them.

So soil is important for farming, as it provides nutrients for crops, having blank scale economic benefits for farmers.

And soil is important on a blank scale, as it absorbs carbon, helping in the fight against climate change.

So your two options could be local or global, and I'd like you to put the correct scale into the correct sentence.

Well done for giving that a really good go.

Let's check your answers.

So soil is important for farming, as it provides nutrients for crops, having local scale economic benefits for farmers.

And soil is important on a global scale, as it absorbs carbon, helping in the fight against climate change.

Brilliant work, geographies.

You're doing an excellent job.

So despite how important it is, one third of the Earth's soil has already been damaged by human activities, and there are some quite significant threats to soil all around the world.

The first one is pollution, because this kills living organisms in the soil and can then affect the quality of that soil.

We then have deforestation, as this disturbs the structure and removes the protection from the trees, making it more vulnerable to erosion.

So deforestation is where we remove vegetation from the landscape.

And as we can see there, it makes it more vulnerable to erosion because it becomes more exposed.

Then we have climate change, and this is where higher temperatures can dry out the soil.

And we know that things like water are really important to that soil.

And lastly, we have urbanisation.

Now covering the grounding concrete and buildings prevents the soil from absorbing water, which we've already established is really important to having good quality soil.

So we can see here that there are some quite significant threats to soil despite it being really important.

So we're gonna put this into practise, and I'd like you to write a letter to your local Member of Parliament, or your MP, explaining why they should make soil protection a top priority.

Andeep says, "Writing to your local MP shows you really care about different issues and encourages the MP to also care." So I'd like you to tell the MP why soil is really important, and then talk about what the threats are to it.

And conclude with why they should make it a priority to protect it.

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

Well done for having a really good go at that, geographers.

Now you could have included something similar to mine in your answers, although it's likely to be slightly different.

But let's check and see what you could have included.

"Dear local MP, I am writing to you as a young geographer and a concerned citizen to ask that you make soil protection a top priority in your work as our Member of Parliament.

Soil is not just dirt.

It's a living system made up of minerals, water, organic matter, and air.

It's vital for growing food, supporting wildlife, and storing carbon, which helps fight climate change.

But despite its importance, soil is being damaged by pollution, erosion, and poor farming practises.

Without healthy soil, farmers will struggle to grow crops, which we need on a large scale for all communities.

Damaged soil also releases carbon into the atmosphere, making climate change worse.

Protecting our soul means protecting our future.

Please consider supporting policies that protect soil and our natural environment.

Our generation, and those to come, are counting on leaders like you to act now.

Yours sincerely, Sofia." Thank you, Sofia.

That was a really persuasive letter to the MP encouraging them to promote soil protection.

Well done for giving that a really good go.

And I'm sure all of your letters are looking fantastic.

So we've now come to the end of our lesson on the importance of soil.

And we've learned a couple of really important points.

Soil is made up of minerals, organic matter, water and air.

Soil takes hundreds of years to form.

There are three main particle sizes in soil: clay, sand, and silt.

Soil is important for farming.

Infertile soil can make growing crops very difficult.

And lastly, soil is an important carbon store, and protecting it can help us reduce the rate of global temperature increase.

So well done for engaging so well in today's lesson, geographers.

You've done a really brilliant job.

And I really look forward to seeing you in our next lesson.