hey everybody it's mr. Smith's 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 soils so we'll be really focused on how soil forms and really what it is we have to know that soils 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 gonna be doing in Apes though this year that were 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 houmous houmous 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 wastes 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 space 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 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 habitats so soil provides a valuable habitat to organisms like earthworms fungi bacteria even moles or other mammals that live underground our 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 a breakdown of rocks now it can happen in three ways it can happen by the wind in 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 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 a rosin to take place as well so if weathering is the breakdown of rock erosion is the transport of those little pieces of rocks 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 creates 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 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 so information from above so the grass and the plants that you can see up here they're gonna die eventually and when decomposers break their bodies down they will contribute houmous to the soil and that's going to really contribute to you 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 after roots 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 near by a more steep slope that's going to lead to a lot of soil deposition and that can increase the rate of star 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 human 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 gonna have high rates of soil formation because we're gonna get a lot of weathering and it's gonna 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 you Road the soil and so that can decrease the rate of star 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 the activity the faster the rate of soil formation because we're getting breakdown of organic matter that's contributing to more human 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 characters six so the first one is the Oh 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 topsoil and this is a layer largely of houmous which is decomposed organic matter that came from the AU 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 gonna sit beneath the a horizon and it's gonna be a little bit lighter in color because there's typically going to be more clay and less human human 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 gonna be little to no organic matter down in the B horizon it will could 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 a is soil degradation so sort of a gradation 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 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 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 are pulled over bulldozers things like grazing livestock so cattle and then even just humans walking 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 is 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 I suggested science skill for practice up rq-4 point to 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