Layers of the Atmosphere
The Earth’s atmosphere is beautiful, wonderful, and perfect for sustaining life. She’s also a complex, interesting character with depth and layers. See for yourself: Take a (virtual) journey in a weather balloon up through her many layers. Tip: This video is in 360°! Look around using the arrows in the top left corner of the video:
What an interesting and 3-dimensional lady. Like an onion, or an ogre.
Why Does the Atmosphere Have Layers?
In the last part of this lesson, we learned about the composition of the atmosphere and introduced the idea of gravity as it relates to mass. As a reminder: more mass = more gravity. Gravity is also related to distance: the farther away something is, the weaker the gravitational pull. As you move farther away from the surface of Earth, Earth’s ability to hold onto gases becomes weaker. So, there are fewer gas molecules way out there. In other words, density decreases as you move away from the Earth’s surface.
You also previously learned about how that difference in density relates to pressure. The inner core has A LOT of stuff on top of it pushing down onto it, so it gets squished. The same is also true of the atmosphere. The innermost layer of the atmosphere has a lot of stuff pushing down on it (compared to the outermost layers, which are just surrounded by space). Because of this, once again, density decreases as you move away from the Earth’s surface.
Both the gravity explanation and the pressure explanation are important in explaining the trend of Earth and atmospheric density.
You first learned about the relationship between layers and density when we talked about the layers of the Earth. Let’s take another look:
You also previously learned about how that difference in density relates to pressure. The inner core has A LOT of stuff on top of it pushing down onto it, so it gets squished. The same is also true of the atmosphere. The innermost layer of the atmosphere has a lot of stuff pushing down on it (compared to the outermost layers, which are just surrounded by space). Because of this, once again, density decreases as you move away from the Earth’s surface.
Both the gravity explanation and the pressure explanation are important in explaining the trend of Earth and atmospheric density.
You first learned about the relationship between layers and density when we talked about the layers of the Earth. Let’s take another look:
This is the exact same pattern we see with the atmosphere: closer to the center of Earth = higher density.
These regions of different density can be divided into layers based on the unique composition and properties of the layers that correspond to the different densities.
So, now you know why the atmosphere has layers and why these layers get less dense as you move away from Earth: Gravity has a stronger pull on the air molecules closer to Earth (and therefore pulls them in tighter, only barely grabbing the strays at the outer limits of the atmosphere), and the air closest to earth gets compressed by the weight of all the air on top of it. Now, let’s take a look at each layer and find out what interesting and important things happen in each.
Troposhere
Let’s start with the layer closest to Earth. The troposphere stretches about 10 km (6 miles) up from the earth’s surface. The air all around you is troposphere. This layer has just the right combination of nitrogen and oxygen to sustain living things. The weather we experience, including changes in wind pressure, temperature, and moisture, is created in the troposphere.
As you go up farther away from the earth’s surface in this layer, the temperature generally decreases. This happens because the earth’s surface absorbs heat energy from the sun, and radiates that energy back out. The further you go, the less heat is radiated outwards. Near the surface, the temperature is about 10 to 20 °C (50 to 70 °F, depending on the weather where you live), while near the top it is around –60 °C (–75 °F)!
Remember, the density decreases as you go up!
As you go up farther away from the earth’s surface in this layer, the temperature generally decreases. This happens because the earth’s surface absorbs heat energy from the sun, and radiates that energy back out. The further you go, the less heat is radiated outwards. Near the surface, the temperature is about 10 to 20 °C (50 to 70 °F, depending on the weather where you live), while near the top it is around –60 °C (–75 °F)!
Remember, the density decreases as you go up!
Stratosphere
The stratosphere is the second layer of the atmosphere. It starts somewhere between 10 and 18 km (6-12 miles) depending on the latitude. Commercial airplanes could fly through the stratosphere, especially when they’re going long distances (airlines typically fly at 10 km, or about 30,000 ft).
The stratosphere is stratified in temperature (hey, I wonder if that’s where it gets its name?). Before the ozone layer, the temperature keeps getting colder as you move away from Earth, for the same reason that the troposphere gets warmer farther from Earth. Past the ozone layer, the temperature gets hotter as you move away from earth. This is because it no longer has the ozone layer to protect it from the sun, but, unlike the next layer (the mesosphere), it still has enough density to hold onto that heat.
The stratosphere is stratified in temperature (hey, I wonder if that’s where it gets its name?). Before the ozone layer, the temperature keeps getting colder as you move away from Earth, for the same reason that the troposphere gets warmer farther from Earth. Past the ozone layer, the temperature gets hotter as you move away from earth. This is because it no longer has the ozone layer to protect it from the sun, but, unlike the next layer (the mesosphere), it still has enough density to hold onto that heat.
The ozone layer is a thin layer of the gas ozone (I wonder if that’s why it’s called the ozone layer?), which is found in the stratosphere.
As you’ve learned, the ozone layer (thanks to all the ozone in it) protects against harsh ultraviolet (UV) rays from the sun. You may already know that UV radiation causes sunburn. More severe effects include skin cancer, premature aging of the skin, and cataracts in your eyes. Oxidants (molecules in the same chemical class as ozone) in sunscreen protect from these UV rays. Ozone is really just the Earth’s sunscreen.
Unfortunately, the ozone layer is rapidly deteriorating due to chemical pollution, especially from factory emissions. Environmental regulations around factory emissions are trying to protect the ozone, but varying levels of enforcement and compliance mean that we still haven’t fixed the problem.
As you’ve learned, the ozone layer (thanks to all the ozone in it) protects against harsh ultraviolet (UV) rays from the sun. You may already know that UV radiation causes sunburn. More severe effects include skin cancer, premature aging of the skin, and cataracts in your eyes. Oxidants (molecules in the same chemical class as ozone) in sunscreen protect from these UV rays. Ozone is really just the Earth’s sunscreen.
Unfortunately, the ozone layer is rapidly deteriorating due to chemical pollution, especially from factory emissions. Environmental regulations around factory emissions are trying to protect the ozone, but varying levels of enforcement and compliance mean that we still haven’t fixed the problem.
The ozone layer is thinning over the Antarctic
Mesosphere
Have you heard that meteors have fiery trails as they fall down to earth? Well, that’s because gases in the mesosphere slow down the path of the meteor and cause so much friction that the meteor actually catches fire. It’s like how your hands heat up when you rub them together, times a million. The meteors usually burn up in this layer, saving our earth from harm. Thanks, mesosphere!
The mesosphere is approximately 50-80 km (30-50 miles) above Earth’s surface. As you go higher up the mesosphere, the temperature gets colder because it’s too thin to hold onto heat. The top of the mesosphere is the coldest part of the atmosphere (it’s about –90 °C or –130 °F).
Beyond that, we don’t really know much about the mesosphere because it’s too high for us to look at with weather balloons and too low for us to study with satellites.
The mesosphere is approximately 50-80 km (30-50 miles) above Earth’s surface. As you go higher up the mesosphere, the temperature gets colder because it’s too thin to hold onto heat. The top of the mesosphere is the coldest part of the atmosphere (it’s about –90 °C or –130 °F).
Beyond that, we don’t really know much about the mesosphere because it’s too high for us to look at with weather balloons and too low for us to study with satellites.
Thermosphere
The thermosphere is a part of what is called the upper atmosphere. Unlike in the lower atmosphere, where the gases are all mixed together in about 80% nitrogen, 20% oxygen, and 1% trace gases, the upper atmosphere mainly consists of helium, atomic oxygen (O), and atomic nitrogen (N).
In the thermosphere, O₂ and N₂ get split up into O and N by energy from the sun. This creates charged particles that collide with solar wind to create the aurora borealis, or Northern Lights, and the aurora australis, or Southern Lights. These are the exact same phenomena, only at opposite poles.
In the thermosphere, O₂ and N₂ get split up into O and N by energy from the sun. This creates charged particles that collide with solar wind to create the aurora borealis, or Northern Lights, and the aurora australis, or Southern Lights. These are the exact same phenomena, only at opposite poles.
Auroras seen from International Space Station
The air in the thermosphere is also really, really thin. The gases are so far apart from each other that this layer is mostly considered outer space. This is where the International Space Station orbits Earth!
The air in the thermosphere is so thin that, even though it is the largest layer in terms of distance from the lower limit to the upper limit, it contains less than 0.01% of the atmosphere’s gas. The other 99.99%, save a few stray particles in the exosphere, are in the lower atmosphere.
The thermosphere absorbs a lot of X-rays and UV radiation from the sun, so it is insanely hot. That’s why it’s called the thermo-sphere. We’re talking 500–2000 °C (900–3600 °F)! The range is so big because the temperature is dependent on the sun: the temperature is about 200 °C colder at night than during the daytime (still really hot), and about 500 °C warmer when the sun is really active (you might have heard of something called solar flares, which heat up the thermosphere).
Even though the thermosphere is really hot, it would feel cold to you, and most thermometers would read the temperature as really cold (around 0 °C, freezing temperature). That’s because the air is so thin that molecules don’t collide often enough to transfer heat. You can think of this like a really hot stove that you are all the way across the room from: you would definitely get burned if you touched the stove, but you probably won’t, so you don’t notice the heat.
The air in the thermosphere is so thin that, even though it is the largest layer in terms of distance from the lower limit to the upper limit, it contains less than 0.01% of the atmosphere’s gas. The other 99.99%, save a few stray particles in the exosphere, are in the lower atmosphere.
The thermosphere absorbs a lot of X-rays and UV radiation from the sun, so it is insanely hot. That’s why it’s called the thermo-sphere. We’re talking 500–2000 °C (900–3600 °F)! The range is so big because the temperature is dependent on the sun: the temperature is about 200 °C colder at night than during the daytime (still really hot), and about 500 °C warmer when the sun is really active (you might have heard of something called solar flares, which heat up the thermosphere).
Even though the thermosphere is really hot, it would feel cold to you, and most thermometers would read the temperature as really cold (around 0 °C, freezing temperature). That’s because the air is so thin that molecules don’t collide often enough to transfer heat. You can think of this like a really hot stove that you are all the way across the room from: you would definitely get burned if you touched the stove, but you probably won’t, so you don’t notice the heat.
Exosphere
The outermost layer of the atmosphere is called the exosphere. It starts at about 500-1000 km and goes out to about 10,000 km before it is officially considered outer space. This range includes Low Earth orbit (160 km to 2,000 km) and Medium Earth orbit (2,000 km to 36,000 km) satellites. The majority of communication and navigation satellites orbit outside of the exosphere at around 20,000 km.
The exosphere is also where molecules and atoms escape into space. It is even hotter than the thermosphere (because it is less shielded), but feels even colder because the molecules are even farther apart than they are in the thermosphere.
The exosphere is also where molecules and atoms escape into space. It is even hotter than the thermosphere (because it is less shielded), but feels even colder because the molecules are even farther apart than they are in the thermosphere.
Summary
This video gives a good overview of the layers of the atmosphere:
This is another good video, which gives similar information but does a little bit of a better job of explaining the temperature changes:
You should know:
- How and why density changes as you go further out in the atmosphere.
- The names of each level of the atmosphere, and some of the important things that happen there:
- Troposphere: The level we live in. Most weather happens here.
- Stratosphere: Airplanes fly here. The ozone layer is found here, which absorbs harmful UV rays from the sun.
- Mesosphere: Meteors get burned up here.
- Thermosphere: The upper atmosphere/”lower outer space”. Absorbs most X-rays and UV radiation from the sun. The aurora borealis (Northern lights) occur here. The international space station orbits here.
- Exosphere: The upper atmosphere/”lower outer space”. Most molecules and atoms escape into outer space. Low- and medium-orbit satellites orbit here.
- How temperature varies through each level of the atmosphere (in to out):
- Troposphere: hot to cold, because the reflection of the sun off of the earth is warmest close to Earth.
- Stratosphere: past the Ozone layer, cold to hot, because the sun is heating it up further out (and the Ozone is no longer protecting it from the sun).
- Mesosphere: hot to cold, because it can’t hold onto heat (and the very high energy X-rays and UV rays that would manage to heat it up anyways are all absorbed in the thermosphere).
- Thermosphere: cold to hot, because it is absorbing more X-rays and UV rays from the sun further out.
Learning Activity
Content contributors: Cathleen Kong, Emma Moulton