By all scientific standards, the existence of planet Earth is improbable. Our blue and green planet supports life, thanks to an envelope of gases that keep heat in and harmful radiation out. The atmosphere keeps temperatures comfortable for life and allows for liquid water to form on the planet’s surface.
Did you know that the atmosphere has multiple layers? Earth’s atmosphere is not just one invisible sphere of gasses. It’s actually 5 layers divided by their temperature gradient.
There are levels of atmosphere that change depending on how high above ground level you are. The cardinal measurement to determine what level of atmosphere something is in is temperature. There are different temperature gradients in each of the five atmospheric layers. The dividing line between layers is where that gradient changes.
This article will teach you about the five layers of the atmosphere. You’ll learn what each layer contains, the level of altitude it begins and ends at, and common activities within it.
5 Layers of the Atmosphere
First, let’s discuss the way we measure the level of atmosphere. The layers of Earth’s atmosphere are divided based on a temperature gradient.
You encounter temperature gradients in daily life. For example, as you walk closer to a campfire, the air temperature grows hotter. The same is true with the gradients in the levels of the atmosphere.
You might expect the air to simply grow colder the further away it is from Earth. However, that is not always the case.
The stratosphere and thermosphere are hotter at their outer edges than they are at their inner borders. This is because their heat source comes not from Earth, but from outer space – thanks to heat and light from the sun.
Primary Layers
These layers of the atmosphere have clear delineations between each other. They each have a temperature gradient and several main qualities that set them apart from each other.
1. Troposphere
The troposphere is where 99% of life spends its time. Even though it is the thinnest layer of Earth’s atmosphere, it has the highest level of activity. The troposphere ranges from the highest elevation point of land – about 5.5 miles – to 9 miles above sea level. Almost all activity on earth happens in this 9 mile and under window.
Almost all human activity occurs within the troposphere. Commercial air liners usually fly at about 25,000 – 35,000 feet, or 4.75 to 6.6 miles above sea level. They stay well under the 9 mile limit of the troposphere.
Ecological activity also happens in the troposphere. It’s thanks to abundant movement of the air because of weather and climactic changes. Here, the air is dense enough to support life. Compared to all other layers of the atmosphere, the troposphere has the highest quantity of gases – 75%!
These gases include 78% nitrogen, 21% oxygen, and 1% water vapor, argon, and carbon dioxide. The high percentage of oxygen makes life possible.
Oxygen is more abundant in air closer to sea level. As one gets higher in altitude, there is less oxygen in the air and it’s harder to breathe. The troposphere concentrates oxygen close to the earth’s surface, providing life forms with enough oxygen to conduct respiration.
The presence of water vapor in the troposphere is crucial too. Most clouds, including stratospheric and cumulus clouds, form and dissipate within the troposphere.
Water is abundant in this layer of the atmosphere. It usually stays within the troposphere because the water cycle does not propel it upwards and farther away from earth. Instead, cloud formation brings water vapor as high up as the troposphere, where it coalesces and falls back down to earth as precipitation.
The dynamic nature of the water cycle shakes up the balance of gases in the troposphere. It causes weather events, which form into the patterns that support biotic life.
Temperature ranges in the troposphere mirror those of the surface of Earth. Since the earth’s reflective heat patterns are the source of the heat in the troposphere, the farther out in the troposphere one gets, the colder the air temperature.
2. Stratosphere
The stratosphere is the second layer of Earth’s atmosphere. It begins at about 7 miles (depending on where you are on earth, the troposphere ends at a higher or lower altitude) and extends upwards until 31 miles above the surface of the earth.
Rockets travel through this layer to reach outer space or orbit as satellites. Some planes can also venture into the lowest reaches of the stratosphere.
Compared to the troposphere, the stratosphere is a very quiet place to be. It doesn’t have weather patterns to shake up its molecules, so the temperature gradient is very pronounced.
Despite its humble status, the stratosphere has been in the news for the last 60 years because of its connection to the ozone layer. The ozone layer is within the stratosphere. It absorbs harmful UV rays from the sun that would injure natural life on the planet.
Clouds can occasionally be found in the stratosphere. There is very little water vapor compared to the troposphere, but in the earth’s polar regions, there is enough to make stratospheric clouds when conditions are very cold.
3. Mesosphere
The middle layer of Earth’s atmosphere is named ‘mesosphere,’ after the Latin word for ‘middle.’ The peaceful mesosphere starts at around 31 miles and ends at 50 miles. It’s sandwiched between the stratosphere and the thermosphere.
The average temperature of the mesosphere is -120 F (-85C). This makes it one of the coldest places on Earth. It contains just enough water vapor to create small, wispy clouds. These clouds are called noctilucent cloud. They’re very hard to spot, but they can still be seen without binoculars.
Scientists call the mesosphere the ‘atmospheric layer of meteors’ because most meteors that collide with Earth actually burn up upon entering the mesosphere. These space rocks burn because they experience intense friction from flying through the air of the mesosphere.
Air density of the mesosphere isn’t high. However, it’s higher than in the two upper layers – the thermosphere and the exosphere. The meteor doesn’t encounter much resistance when it flies through those layers. Everything changes when it enters the mesosphere – there are more gases there. Meteors travel so fast that the friction they cause makes enough heat to set them on fire.
Most meteors burn up completely upon entering the atmosphere. The few meteors that have crash landed to earth are the exception, not the rule.
Humans rarely visit the mesosphere. It’s usually a pass-through zone for rockets carrying space exploration vehicles or satellites. There are some rocket-powered aircraft that can reach this zone too.
4. Thermosphere
The thermosphere is so named because of its temperature gradient. As the location in the thermosphere increases, so does the air temperature. This happens because the thermosphere is absorbing energy from the sun, which creates heat.
A secondary layer of the earth’s atmosphere is based in the thermosphere. The ionosphere enables radio communications, making it possible for people to connect and communicate all over the world. Without it, air-based communication methods would be all but impossible.
The thermosphere’s altitude ranges from 50 to 440 miles above sea level. It’s the second-largest level of the atmosphere but it contains no water vapor and thus, no clouds.
It sees very little activity, which makes it a great location to set up the International Space Station. There is no risk of weather events or plane fly-bys that would disturb the astronauts and their equipment.
Inhabitants of and visitors to the polar regions of Earth have the opportunity to see the aurora borealis. This beautiful ribbon of colored light is a sight to behold.
5. Exosphere
Its bottom borders the thermosphere and its upper edge butts up against outer space. The exosphere is the last layer of Earth’s atmosphere. It’s also the largest. It ranges from 440 – 6,200 miles above the surface of the earth.
Even though the exosphere is large, it is one of the most well-known layers of the atmosphere. Why? It is the zone where satellites orbit the earth. Many man-made objects whiz around the planet in the exosphere each day.
Atoms whiz around here too. There are very few atoms in the exosphere. The ones that are present are not bounded to the earth very strongly. Some even escape into space!
Few people have ever traveled past the exosphere. You can see the exosphere from earth, however. Like in the thermosphere, the aurora borealis is visible here, in the lowest level of the layer.
Secondary Layers
The secondary layers of the atmosphere do not have temperature gradients like the major layers do. They are layers independent of temperature gradients. They don’t follow dividing lines in the same way that the
Ionosphere
The ionosphere is not an atmospheric layer like the other layers discussed in this article. It doesn’t have a temperature gradient, nor is it visible. However, the discovery and use of the ionosphere plays a critical role in human history and progress. Why? The ionosphere enables radio communications.
Radio communications rely on reflected radio waves to bounce a radio signal back and forth between stations. The ions created by the sun’s rays in the ionosphere do just that.
They bounce radio signals between each other. Like links in a chain, the signal is passed between one ion and the next, allowing people from other sides of the world to hear each other’s radio broadcasts.
Ozone Layer
The ozone layer is invisible, like all the layers of Earth’s atmosphere, but it plays an extremely important role in protecting all life on earth. It prevents most of the sun’s ultraviolet radiation (UV rays) from reaching the earth. This layer absorbs the UV rays.
When the sun issues light, it also issues out UV rays. There are two kinds – UV-A and UV-B. UV-A rays, the more harmful kind, are mostly blocked by the ozone layer. These rays, which cause cancer, can be a health risk to life on earth.
The successful recovery of the ozone layer is a success story for people around the world. Until two decades ago, there was a significant hole in the ozone layer. This hole, which was expanding, was letting in harmful UV-A rays into the troposphere. It was caused by the release of gases and smog from combustion vehicles and chlorofluorocarbons (CFCs).
Thanks to some stringent environmental practices like increasing catalytic converter use, banning CFCs, and improving the efficiency of gas-powered motors, the hole in the ozone layer stopped expanding and eventually began to shrink.
Anna is a wildlife biologist who graduated from Texas A&M in 2020. She enjoys studying and learning about wild birds and wildlife of all types.