Understanding Soil Formation and Erosion

Hey everybody, it's Mr. Smeeds, and today we're talking about topic 4.2, which is soil formation and erosion. Soil is an incredibly important topic in APES. It's going to serve as the foundation for our understanding of how plants grow, how water is filtered, and so many other important functions that soil plays. So let's take a look at our objectives and our essential knowledge and our skills for the day. So our learning objective today is to describe the characteristics and formation of soil. So we'll be really focused on how soil forms. and really what it is. We have to know that soil is formed when parent material, which is the rock underlying soil, is weathered or broken down and then transported and deposited. We also have to know that soils are categorized by different horizons or layers. We'll talk about the characteristics of those. And then we also need to know that soil can be eroded by winds or water. And then we can talk about how soil is degraded or what can happen to lower its ability to grow plants. Our suggested science skill for the day is to identify a research method, design, or measure to be used to conduct an experiment. So we'll talk about that at the end of the video. So what is soil? Before we get started here, we have to talk about what soil actually is. It's really misunderstood. A lot of times we call it dirt. We know that's not something we're going to be doing in apes though this year, that word is not allowed in this class. And so we'll talk about what it is and why it's important. So soil is a mix of geological and organic components. So these are rock-based components and components that come from living things. Either they are alive right now or they were once living. So first we have sand, silt, and clay. Those are the three main particles that make up soil. We'll talk about those in tomorrow's video. Then we have humus. Humus is the main organic component of soil. It's that dark, rich, black substance that kind of gives soil its characteristic color and even its smell. It's broken down organic matter like dead plants, dead leaves, animal waste, even dead animals. Then we have nutrients in the soil. So things like ammonium, phosphates, and nitrates. These are going to be really critical for plant growth. We have water and air. Even water and air are part of the soil. They fill the little spaces or pores in the soil. And air is important because it has oxygen that plants'roots need. And of course, they need water as well. So we need to have air and water in the soil. And then finally we have living organisms, so earthworms, fungi, bacteria, other decomposers that are going to help recycle nutrients. Now we'll talk about four really important roles that soil plays in ecosystems. So the first is that it supports plant growth. It's going to serve as an anchor for plant roots and it's going to provide them with the water and the nutrients that they need. So these are things like nitrogen, potassium, phosphorus, magnesium, and we can see this tree here has established its roots and that's going to help hold it up. Also, we have water. Soil is a really important water filtration system. So when runoff or rain starts to trickle or percolate through a soil, the spaces in the soil, the pore spaces will actually trap pollutants so that clean water can pass through and recharge groundwater sources and aquifers. Then we have nutrient recycling. So all of the decomposers in a soil are going to break down the dead organic matter. and they're going to return those vital nutrients to the soil. So it's really critical that we have soil for the purpose of recycling nutrients that are needed for new growth. And then finally, we have habitat. So soil provides a valuable habitat to organisms like earthworms, fungi, bacteria, even moles or other mammals that live underground are really benefit from having that habitat. Now we'll talk about weathering and erosion. They're very important. And sometimes they're confused with each other, so we have to be sure that we understand what they are. So weathering is just the breakdown of rocks. Now, it can happen in three ways. It can happen by the wind and the rain, which we call physical weathering. It can happen by chemicals. So there could be acids that are in rain, acid precipitation. That could break down a rock. And then we even have biological breakdown, which is trees that have roots that actually grow into the cracks of the rocks and break it down. One other way that... physical weathering happens is rain seeping into the cracks of rocks and then when it freezes it expands and that breaks the rock open further once we get weathering of rock that's how we actually start soil formation so those bits of rocks are broken down into smaller and smaller pieces and those are the pieces that will ultimately make up soil but before that happens we need erosion to take place as well so if weathering is the breakdown of rock erosion is the transport of those little pieces of rock. So we have a great diagram here. We can see that as the rain falls, it's going to detach or break off little bits that have been weathered. then it's going to transport them and move them somewhere else and then ultimately it's going to deposit them so deposition is the last step of erosion and we can see soil is starting to build up in layers here so erosion is critical to soil formation as well and together weathering and erosion are what actually create soil we break rocks down to smaller bits weathering and then the wind and the rain carry those little bits somewhere else and deposit them erosion and that's soil formation Now we'll talk in a little more depth about soil formation and factors that affect soil formation. So first we have soil formation from below. This is the weathering or breakdown of parent material. Parent material, sometimes called bedrock, is the rock that underlies soil. So all soil has rock beneath it if you go deep enough and the weathering or breakdown of that parent material is going to produce smaller and smaller bits of rock that will eventually work their way up and that will form much of the inorganic or the geological part of soil. So this is going to contribute a lot of the sand, silt, and clay and a lot of the minerals. Then we also have soil formation from above. So the grass and the plants that you can see up here, they're going to die eventually. And when decomposers break their bodies down, they will contribute humus to the soil. And that's going to really contribute to the soil nutrient levels. And it's going to add to the depth of the soil. Then we also have the weathering and erosion that we talked about on the last slide. Weathering and erosion can... break down rocks and carry the little bits of rock and deposit them into a soil, which also adds to its formation. Now we'll talk about a few factors that affect the rate of soil formation. So the first one is parent material. Depending on what sort of parent material you have, the soil can take on different attributes of that parent material. So it's going to determine the soil pH and the nutrient content. So for instance, if we have a soil that has limestone bedrock, That's going to lead to a lot of calcium in the soil, which is good for plant growth. It also helps to buffer acidic soil. So limestone can be a really beneficial parent material or bedrock to have. Then we have topography. So if the slope is too steep in an area, then soil formation will really be hindered because so much soil is going to be eroded away from that area. And that's going to slow down the rate of soil formation. On the other hand, if you have more level ground, especially nearby a more steep slope, that's going to lead to a lot of soil deposition and that can increase the rate of soil formation then we have climate so the warmer an area is the faster generally the breakdown of organic matter is and so that's going to lead to an increased rate of soil formation as that dead organic matter gets turned into humus at a much faster rate on the other hand if it's colder that's going to really slow down the rate of biological activity which really slows down the rate of soil formation all that dead organic matter is just going to kind of build up Precipitation is another factor of climate that can affect the rate of soil formation. When we have really high precipitation, we're going to have high rates of soil formation because we're going to get a lot of weathering and it's going to break down the rock and contribute more little rock fragments that build up the soil. However, if there's too much wind or too much rain in an area, this can also erode the soil and so that can decrease the rate of soil formation. So rain and wind really can impact soils in different ways depending on the slope and all the other factors. Then we have soil organisms. So decomposers like earthworms, fungi, and bacteria, they have a really important role to play in soil formation as well. The higher the activity of the decomposers in an area, meaning the more of them there are and the warmer it is to support their activity, the faster the rate of soil formation because we're getting breakdown of organic matter that's contributing to more humus and a deeper soil. Now we'll talk about soil horizons or sometimes called soil profiles. So we're looking at a cross section here of soil and we'll go through the different layers and talk about each of their important characteristics. So the first one is the O horizon. This is a shallow layer of primarily organic material that rests on top of the soil. So this is going to be mostly things like plants roots, dead leaves, animal waste that lays on top of the soil. It's really important because one it provides the nutrients that will essentially be nourishing plant growth in the future after they're broken down, but it also acts as kind of a moisturizing layer. It traps moisture into the soil and prevents it from being evaporated. So organic matter on top of your soil is really important. Then we have the A horizon, sometimes known as the top soil. And this is a layer largely of humus, which is decomposed organic matter that came from the O layer, and then minerals that come from the parent material below. The A horizon is extremely important because it houses most of the biological activity. So most of the breakdown of organic matter will happen in the A horizon, which also means it's going to hold much of the nutrients of a soil. Then we have the B horizon, also known as the subsoil. That's going to sit beneath the A horizon. It's going to be a little bit lighter in color because there's typically going to be more clay and less humus. Humus is, remember, the black sort of dark component of soil that gives it its characteristic color that we think of when we think of soil. And there's going to be little to no organic matter down in the B horizon. It will still contain some nutrients though. Then when we get down to the C horizon, this is the least weathered or the most intact. rock, it's going to be similar to the parent material or sometimes what we refer to as the bedrock day is soil degradation. So soil degradation is the loss of the ability of soil to support plant growth. And this is a really harmful thing. We'll talk about how it happens here. So first, we'll talk about the loss of topsoil. So one common cause for the loss of topsoil is tilling. This is turning the soil for agriculture to make it a little bit easier to plant your seeds. But it's going to make the soil be disturbed and a lot more easily eroded by wind and rain. Also, the loss of vegetation can make the soil more prone to being eroded because the roots of plants are really important stabilizing structures. So the loss of topsoil has a lot of negative effects on the productivity of that soil. It's going to dry out the soil because we're losing that organic layer that was very moisturizing, traps moisture in. We're losing a lot of the nutrients contained in the topsoil. we're also losing a lot of the organisms that are recycling nutrients. So really kind of a triple whammy when the topsoil is lost. Then we have compaction. So compaction is the compression of soil by machines, things like tractors or bulldozers, things like grazing livestock, so cattle, and then even just humans walking in an area can cause soil compaction. The problem with soil compaction is it forces the soil particles closer together. which eliminates the pore space, which is really vital for holding water. So think of soil as kind of like a sponge. If you squeeze it or smash it down, it can't hold moisture as well. And so that's a problem because dry soil erodes more easily, but also dry soil supports less plant growth. And then the third way that soil is degraded is kind of a byproduct of the loss of topsoil, and that's nutrient depletion. So when you repeatedly grow crops on the same soil over and over again, Each year they remove some of the nutrients that are found there. And as they do that, that soil is going to be less productive or less able to support plants in the future. So a suggested science skill for practice of our Q4.2 today is to identify a research method, design, or measure to be used. So I want you to practice by trying to design an investigation to measure the effect that climate has on soil formation. You need to identify the independent variable and the dependent variable in this investigation.

So our learning objective today is to describe the characteristics and formation of soil. So we'll be really focused on how soil forms. and really what it is. We have to know that soil is formed when parent material, which is the rock underlying soil, is weathered or broken down and then transported and deposited.

We also have to know that soils are categorized by different horizons or layers. We'll talk about the characteristics of those. And then we also need to know that soil can be eroded by winds or water. And then we can talk about how soil is degraded or what can happen to lower its ability to grow plants.

Our suggested science skill for the day is to identify a research method, design, or measure to be used to conduct an experiment. So we'll talk about that at the end of the video. So what is soil? Before we get started here, we have to talk about what soil actually is. It's really misunderstood.

A lot of times we call it dirt. We know that's not something we're going to be doing in apes though this year, that word is not allowed in this class. And so we'll talk about what it is and why it's important.

So soil is a mix of geological and organic components. So these are rock-based components and components that come from living things. Either they are alive right now or they were once living. So first we have sand, silt, and clay.

Those are the three main particles that make up soil. We'll talk about those in tomorrow's video. Then we have humus.

Humus is the main organic component of soil. It's that dark, rich, black substance that kind of gives soil its characteristic color and even its smell. It's broken down organic matter like dead plants, dead leaves, animal waste, even dead animals. Then we have nutrients in the soil. So things like ammonium, phosphates, and nitrates.

These are going to be really critical for plant growth. We have water and air. Even water and air are part of the soil.

They fill the little spaces or pores in the soil. And air is important because it has oxygen that plants'roots need. And of course, they need water as well.

So we need to have air and water in the soil. And then finally we have living organisms, so earthworms, fungi, bacteria, other decomposers that are going to help recycle nutrients. Now we'll talk about four really important roles that soil plays in ecosystems.

So the first is that it supports plant growth. It's going to serve as an anchor for plant roots and it's going to provide them with the water and the nutrients that they need. So these are things like nitrogen, potassium, phosphorus, magnesium, and we can see this tree here has established its roots and that's going to help hold it up.

Also, we have water. Soil is a really important water filtration system. So when runoff or rain starts to trickle or percolate through a soil, the spaces in the soil, the pore spaces will actually trap pollutants so that clean water can pass through and recharge groundwater sources and aquifers. Then we have nutrient recycling. So all of the decomposers in a soil are going to break down the dead organic matter.

and they're going to return those vital nutrients to the soil. So it's really critical that we have soil for the purpose of recycling nutrients that are needed for new growth. And then finally, we have habitat.

So soil provides a valuable habitat to organisms like earthworms, fungi, bacteria, even moles or other mammals that live underground are really benefit from having that habitat. Now we'll talk about weathering and erosion. They're very important.

And sometimes they're confused with each other, so we have to be sure that we understand what they are. So weathering is just the breakdown of rocks. Now, it can happen in three ways.

It can happen by the wind and the rain, which we call physical weathering. It can happen by chemicals. So there could be acids that are in rain, acid precipitation. That could break down a rock. And then we even have biological breakdown, which is trees that have roots that actually grow into the cracks of the rocks and break it down.

One other way that... physical weathering happens is rain seeping into the cracks of rocks and then when it freezes it expands and that breaks the rock open further once we get weathering of rock that's how we actually start soil formation so those bits of rocks are broken down into smaller and smaller pieces and those are the pieces that will ultimately make up soil but before that happens we need erosion to take place as well so if weathering is the breakdown of rock erosion is the transport of those little pieces of rock. So we have a great diagram here.

We can see that as the rain falls, it's going to detach or break off little bits that have been weathered. then it's going to transport them and move them somewhere else and then ultimately it's going to deposit them so deposition is the last step of erosion and we can see soil is starting to build up in layers here so erosion is critical to soil formation as well and together weathering and erosion are what actually create soil we break rocks down to smaller bits weathering and then the wind and the rain carry those little bits somewhere else and deposit them erosion and that's soil formation Now we'll talk in a little more depth about soil formation and factors that affect soil formation. So first we have soil formation from below.

This is the weathering or breakdown of parent material. Parent material, sometimes called bedrock, is the rock that underlies soil. So all soil has rock beneath it if you go deep enough and the weathering or breakdown of that parent material is going to produce smaller and smaller bits of rock that will eventually work their way up and that will form much of the inorganic or the geological part of soil. So this is going to contribute a lot of the sand, silt, and clay and a lot of the minerals.

Then we also have soil formation from above. So the grass and the plants that you can see up here, they're going to die eventually. And when decomposers break their bodies down, they will contribute humus to the soil.

And that's going to really contribute to the soil nutrient levels. And it's going to add to the depth of the soil. Then we also have the weathering and erosion that we talked about on the last slide.

Weathering and erosion can... break down rocks and carry the little bits of rock and deposit them into a soil, which also adds to its formation. Now we'll talk about a few factors that affect the rate of soil formation.

So the first one is parent material. Depending on what sort of parent material you have, the soil can take on different attributes of that parent material. So it's going to determine the soil pH and the nutrient content. So for instance, if we have a soil that has limestone bedrock, That's going to lead to a lot of calcium in the soil, which is good for plant growth. It also helps to buffer acidic soil.

So limestone can be a really beneficial parent material or bedrock to have. Then we have topography. So if the slope is too steep in an area, then soil formation will really be hindered because so much soil is going to be eroded away from that area. And that's going to slow down the rate of soil formation.

On the other hand, if you have more level ground, especially nearby a more steep slope, that's going to lead to a lot of soil deposition and that can increase the rate of soil formation then we have climate so the warmer an area is the faster generally the breakdown of organic matter is and so that's going to lead to an increased rate of soil formation as that dead organic matter gets turned into humus at a much faster rate on the other hand if it's colder that's going to really slow down the rate of biological activity which really slows down the rate of soil formation all that dead organic matter is just going to kind of build up Precipitation is another factor of climate that can affect the rate of soil formation. When we have really high precipitation, we're going to have high rates of soil formation because we're going to get a lot of weathering and it's going to break down the rock and contribute more little rock fragments that build up the soil. However, if there's too much wind or too much rain in an area, this can also erode the soil and so that can decrease the rate of soil formation.

So rain and wind really can impact soils in different ways depending on the slope and all the other factors. Then we have soil organisms. So decomposers like earthworms, fungi, and bacteria, they have a really important role to play in soil formation as well.

The higher the activity of the decomposers in an area, meaning the more of them there are and the warmer it is to support their activity, the faster the rate of soil formation because we're getting breakdown of organic matter that's contributing to more humus and a deeper soil. Now we'll talk about soil horizons or sometimes called soil profiles. So we're looking at a cross section here of soil and we'll go through the different layers and talk about each of their important characteristics. So the first one is the O horizon.

This is a shallow layer of primarily organic material that rests on top of the soil. So this is going to be mostly things like plants roots, dead leaves, animal waste that lays on top of the soil. It's really important because one it provides the nutrients that will essentially be nourishing plant growth in the future after they're broken down, but it also acts as kind of a moisturizing layer. It traps moisture into the soil and prevents it from being evaporated. So organic matter on top of your soil is really important.

Then we have the A horizon, sometimes known as the top soil. And this is a layer largely of humus, which is decomposed organic matter that came from the O layer, and then minerals that come from the parent material below. The A horizon is extremely important because it houses most of the biological activity. So most of the breakdown of organic matter will happen in the A horizon, which also means it's going to hold much of the nutrients of a soil.

Then we have the B horizon, also known as the subsoil. That's going to sit beneath the A horizon. It's going to be a little bit lighter in color because there's typically going to be more clay and less humus. Humus is, remember, the black sort of dark component of soil that gives it its characteristic color that we think of when we think of soil.

And there's going to be little to no organic matter down in the B horizon. It will still contain some nutrients though. Then when we get down to the C horizon, this is the least weathered or the most intact.

rock, it's going to be similar to the parent material or sometimes what we refer to as the bedrock day is soil degradation. So soil degradation is the loss of the ability of soil to support plant growth. And this is a really harmful thing. We'll talk about how it happens here.

So first, we'll talk about the loss of topsoil. So one common cause for the loss of topsoil is tilling. This is turning the soil for agriculture to make it a little bit easier to plant your seeds.

But it's going to make the soil be disturbed and a lot more easily eroded by wind and rain. Also, the loss of vegetation can make the soil more prone to being eroded because the roots of plants are really important stabilizing structures. So the loss of topsoil has a lot of negative effects on the productivity of that soil.

It's going to dry out the soil because we're losing that organic layer that was very moisturizing, traps moisture in. We're losing a lot of the nutrients contained in the topsoil. we're also losing a lot of the organisms that are recycling nutrients. So really kind of a triple whammy when the topsoil is lost. Then we have compaction.

So compaction is the compression of soil by machines, things like tractors or bulldozers, things like grazing livestock, so cattle, and then even just humans walking in an area can cause soil compaction. The problem with soil compaction is it forces the soil particles closer together. which eliminates the pore space, which is really vital for holding water. So think of soil as kind of like a sponge.

If you squeeze it or smash it down, it can't hold moisture as well. And so that's a problem because dry soil erodes more easily, but also dry soil supports less plant growth. And then the third way that soil is degraded is kind of a byproduct of the loss of topsoil, and that's nutrient depletion.

So when you repeatedly grow crops on the same soil over and over again, Each year they remove some of the nutrients that are found there. And as they do that, that soil is going to be less productive or less able to support plants in the future. So a suggested science skill for practice of our Q4.2 today is to identify a research method, design, or measure to be used. So I want you to practice by trying to design an investigation to measure the effect that climate has on soil formation. You need to identify the independent variable and the dependent variable in this investigation.

Transcript for:Understanding Soil Formation and Erosion

Transcript for:
Understanding Soil Formation and Erosion