Hey everybody, it's Mr. Smedes, and today we'll be covering topic 4.4, which is the atmosphere. So we'll be focusing on the temperature changes that happen in each layer of the atmosphere, and how those changes actually define the layers. So our objective today is to be able to describe the structure and composition of Earth's atmosphere.
In order to do that, we need to know what the major gases of Earth's atmosphere are, and we need to know their relative abundances, or what percentage of the atmosphere each one makes up. We also need to know that the layers of Earth's atmosphere are based on changing temperature gradients in each one, and we'll talk about why those changes occur at the end of the video. Our suggested science skill for today is to describe characteristics of an environmental concept that's represented visually. So before we talk about Earth's layers, we're going to run through the basic abundance or percentage that each of the gases in Earth's atmosphere represents. So first we have nitrogen at about 78 percent.
Remember though that most of this is in the form of N2 gas, which really isn't reactive or usable for plants on earth without being fixed by bacteria in the soil or by humans combusting fossil fuels to create synthetic nitrogen fertilizers. Then we have oxygen next at about 21%. And this is critical for life on earth, of course, because animals, including humans, use it for respiration.
This is a key apes vocab term that we should know. So it's not enough on an FRQ in apes to say that we... breathe oxygen.
That's just the act of pulling into our lungs. We need to use the word respire or respiration. We need to know that oxygen for respiration is used to break down glucose to form ATP, which is our main energy source. The third most abundant gas in the atmosphere is actually an inert or non-reactive noble gas called argon, and it's about 0.93%. Then we have water vapor.
which depending on the conditions and region can range anywhere from basically zero percent all the way up to four percent. It's also important to know that water, even though it naturally occurs in the atmosphere, is actually considered a greenhouse gas, meaning that it traps the sun's energy in the atmosphere and warms the planet. Now it's not a greenhouse gas that we really need to be concerned about. We don't need to take any actions to reduce water vapor in the atmosphere, because for one, we need water to cycle through the atmosphere, so can precipitate back down to earth eventually, but also it moves through the atmosphere quite quickly.
So it doesn't persist there for months or years like the greenhouse gases that we're more concerned about. And the final gas we'll talk about today is carbon dioxide or CO2. So you may be thinking, well, it's only 0.04% of the atmosphere, but it actually has a tremendous impact on the temperature because it traps the heat coming from the earth's surface, heated by the sun's rays. and it increases the temperature of the atmosphere. That will increase the temperature on land and in the oceans.
So we'll really talk all year about how increasing CO2 levels in the atmosphere impact ecosystems all over the world. So before we look at the temperature gradient that defines Earth's atmospheric layers, we're going to go through each layer and talk about some of the basic characteristics of them so we're familiar with them. So the troposphere is the layer closest to Earth's surface and it's where all of Earth's weather takes place.
It extends up to about 16 kilometers from Earth. And you can remember that the weather takes place here because the prefix tropo comes from the Greek phrase tropos, which means to change. And as we know, weather is always changing.
It's also the densest layer by far because it's the closest to Earth. So the majority of the Earth's water vapor is going to be found in this layer of the atmosphere, along with many other gases. And while ozone is really beneficial in the stratosphere, where it forms a protective layer that blocks us from a lot of cancer-causing UV rays, when ozone informs down near Earth's surface in the troposphere, it's actually considered an air pollutant.
Now, that's because it contributes to the formation of smog. It damages the human respiratory tract, so it can irritate our esophagus. It can damage our lungs, and it can damage the stomata of plants. And these are little...
pores that the plants use in their leaves for taking in CO2 and releasing oxygen. So ozone in the troposphere can be really harmful to humans and plants. Then we have the stratosphere and you can remember S for second since it's the second layer of the atmosphere.
The most notable thing about the stratosphere is the dense ozone layer that forms here which I mentioned earlier helps block UV radiation so that's really beneficial for life on earth. Then we have the mesosphere and you can remember M for middle. And it's important to point out here that with each layer up we move in the atmosphere, The gas molecules get less and less dense as they're further from Earth, and there's also less mass from layers above them pushing them down. Then above the mesosphere we have the thermosphere, and I like to remember that therm refers to heat, and this is the hottest layer. It also absorbs highly damaging x-rays and UV rays, which is vital for life on Earth since those rays could damage our tissues and even be deadly to some organisms.
This layer also contains charged gas molecules, that light up when struck by high energy solar radiation. This produces a really neat effect called aurora borealis or the northern lights. And finally there's the exosphere and you can remember that exo means outside like the exoskeleton of an insect. So this is the outermost layer of the atmosphere and it's really where the atmosphere merges with outer space.
Now we'll take a look at the way that temperature changes within each layer. So it's important to point out that these layers are actually determined by the changes in temperature gradient. So we'll start at the lowest layer and work our way up.
And I want you to keep an eye on the graph over to the left and on these red and blue arrows as we go, because they can remind you what's happening to temperature in each layer. So we'll start at the very bottom of the troposphere, right at Earth's surface. And as we move higher up in the troposphere, away from Earth's surface, it gets colder. Because the Earth's surface is warmed by the sun, and as we're getting further away from it, there's less heat.
So think about climbing up a really tall mountain. It's going to get colder as you get closer to the top. So if we look over at our graph to the left here, we'll see that in the troposphere, this bottom layer, as we move up or further from our surface, our line for temperature is going over to the left, which is over to colder temperatures.
So we have a blue arrow here reminding us that as we go up in the troposphere, it's getting colder. Then we have the stratosphere where it starts to get warmer. So temperature increases as we move up into the stratosphere because the ozone layer at the bottom of the stratosphere is blocking most of the UV rays which are high energy rays from the sun. These rays however hit the top of the stratosphere and warm it up, kind of like the very top layer of a pool in summer or Lake Michigan getting warmed by the sun.
So if we look at our graph over here we can see that after this peak ozone layer which blocks a lot of those high energy UV rays. The stratosphere is going to start to warm back up quite a bit as we get towards this top layer, which is being warmed just like a pool in the summer gets warmed by the sun's rays, by these UV rays that are striking the top of it and warming it up. So then we have a red arrow going back up to remind us that in the stratosphere, we're getting warmer as we move up. Then in the mesosphere, it starts to get colder again because the gas molecules in this layer are very spread out.
So they just really can't absorb much of the sun's energy very effectively. and so they can't heat up very much. So if we look at the graph of the mesosphere, we'll see that as we are moving up, temperature drops back down and we're going to actually reach a point called the mesopause, which is about the coldest temperature ever found on earth. This is about negative 150 degrees Fahrenheit. Then we get to the thermosphere where we're getting closer and closer to the sun and because this layer is absorbing some very high energy UV rays and x-rays, this is going to cause it to heat up dramatically.
up to temperatures as high as 3100 degrees Fahrenheit. So remember that each layer of Earth's atmosphere is characterized by a shift in temperature in the opposite direction. So just remember if you start on Earth and climb up a mountain it starts to get colder, and then with each layer above that temperature gradient is going to change in the opposite direction. Our science practice for the day is describing characteristics of a concept visually. So I want you to try to identify one of the layers of Earth's atmosphere in the diagram here that has an inverse relationship between temperature and altitude, and then describe why that's the case.
All right, everybody. Thanks for tuning in today. Don't forget to like this video if it was helpful.
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