Okay, everyone. In this lesson, we're going to be talking about the water cycle. Now, I know you probably have all heard of the water cycle, but you may not know exactly what it entails. What type of process is this? Well, it's important to understand that the water cycle and many other cycles are biogeochemical cycles. What these are are pathways in which chemical substances cycle through the abiotic and biotic components of the earth. So, there's a water cycle, there's also a phosphorus cycle, and a carbon cycle, and many other different types of cycles that we'll talk about in later lessons. But these are going to be pathways and cyclic pathways that substances like water will take as they move throughout the atmosphere, oceans, streams, rivers, and organisms. So, it's like how water is recycled throughout our planet, and this is a biogeochemical cycle, and there are others which we will learn more about later. What's important to understand is that the water cycle is pretty much the most important biogeochemical cycle. Why? Because every living thing requires water to function. So, the water cycle is pretty important for life on earth. And basically, the water cycle is going to be the flow of water above, on, and below the Earth's surface. So, the water cycle is going to contain the different areas that water can exist. It can exist in the atmosphere via precipitation. It can exist on the ground in lakes and rivers and streams. It can exist inside the ground as aquifers or groundwater, and then it can also flow into the oceans as well.
So, this is going to be a depiction of the water cycle, as you can see here. The water cycle has many different steps, but the major steps are going to be that the oceans, obviously, hold a ton of water. They are going to have sun rays hitting them, and then this is going to cause evaporation, turning liquid water into water vapor, and then this is going to go into the atmosphere and condense into clouds. So, then the atmosphere has clouds which are made of water vapor. And then when those clouds get very saturated with water, we're going to have precipitation, whether that be in the form of ice, snow, sleet, or rain, or anything like that. That is going to be water falling onto the earth, leaving the atmosphere and then going to the earth. And then a lot of things can happen from here. We can have streams fill with water. We can have water seep into or infiltrate into the ground and become groundwater. We can also have it collect in lakes and rivers and streams. Usually, groundwater, rivers, and lakes are going to lead back into the ocean over time, and then that whole process is going to start again.
Now, there are some terms here that you might be interested in. The first one that we have that's a little bit different is sublimation. Sublimation is when a substance goes from a solid form directly into its vapor or gaseous form. So, this would be for water, for whenever it goes from ice into water vapor. It's very difficult to see water do this, and it doesn't do it all that often. You have to have very unique circumstances for this to happen, but this is called sublimation. Desublimation is the exact opposite where water vapor turns directly into ice. But again, this is very difficult to see, and you will probably never witness it. But if you were looking for a great example of sublimation, dry ice turns into carbon dioxide. But again, that is sublimation, but it's not water. Water sublimation is very difficult to visualize. And then there is another word here which is very interesting, evapotranspiration. Evapotranspiration is actually a very specific form of evaporation of water from plants. This is the water vapor that plants release from their bodies. This is commonly called transpiration or evapotranspiration, so a lot of our water in our atmosphere is also coming from plants as well.
So that's what that term means. So now, let's go down and let's talk about some specific types of water that are very important to life on Earth. A very important type of water is groundwater. Any idea why? Because a lot of the fresh water that is utilized for life on our planet is going to be stored as groundwater. Especially for us human beings, a lot of our drinking water and our agricultural water for crops and livestock comes from groundwater. What is groundwater? It is water that sits underground inside soil or rock, and most of it is stored in a specific rocky structure called an aquifer. You probably have heard of an aquifer before, but you might not know exactly what it is. Basically, an aquifer is a layer of rock that is porous, meaning it has holes inside it. So, water-permeable rock. Water can get into those holes in the rock and then be stored there for hundreds or thousands of years. So, aquifers are this porous layer of stone that holds a ton of water. Now in this image up here, this line right here — let me see if I can pick a good color — this line that I'm drawing in red, this is representing groundwater. This is also representing groundwater, and that is water that just exists under the Earth's surface. Now the more specific type of groundwater in aquifers is going to be here. So this, a confined aquifer right here, is going to be that porous rock that is going to hold water inside of those holes in the rock. Now, whenever you are digging into the earth and you hit water, you're going to hit the water table. The water table is the level in the earth or in the ground that is saturated with water. So, basically, once you hit the water table, you've hit the top layer of groundwater, the water being held inside of the ground. And as you can see here, the water table is not very deep. And in many regions of the world, the water table is not very deep, and you can dig maybe 10 feet and hit water. It's a very high water table. In these areas of the world, you probably won't build a basement, but in other areas of the world, you can build a basement because the water table is not so high. So just understand that the water table is that very top layer of groundwater. So, all of this is groundwater here, and then we have a specific aquifer, which is this porous rocky structure that holds water. Now, it's very important to understand that a lot of our water, especially in the United States, around 40 to 50 percent of the water we utilize for drinking and bathing and for our animals and our livestock and our and our crops, comes from groundwater, so it's very important.
Okay, everyone. Let's go on to our next topic.