In the past, I’d heard the reason the Earth’s atmosphere is getting warmer is because the ozone layer is being worn away. That plus pondering how this summer has been so hot and dry here—and because there have been so many raging wildfires—I began to wonder what the current state of the ozone layer is. Then I realized, I don’t actually know a lot about the Earth’s atmosphere and its layers. So—yup!—I decided to look it up.
How about you? Do you know how many layers of atmosphere the Earth has?
Short Answer = Five … but as you may have guessed, it’s a bit more complicated than that.
Long Answer = Earth has five major atmospheric layers plus several secondary layers.
About those five major layers. Can you name them? And do you know what each atmospheric layer does?
1 = Troposphere. We all live in the troposphere; it’s the layer right next to the Earth’s surface up to about 7 ½ miles (or 12 kilometers) high. (But it’s thinner at the poles.) It contains the air we breathe—and also approximately 99% of the water vapor and aerosols in Earth’s atmosphere. Because it holds a relatively large amount of “stuff” (air, particles, clouds, etc…), the troposphere is the densest layer in Earth’s atmosphere.
2 = Stratosphere. The stratosphere sits just above the troposphere reaching about 31 miles (or 50 kilometers) above the Earth’s surface. Polar stratospheric clouds sometimes reach into the stratosphere, but for the most part, no clouds or weather are usually found here. What is found in the stratosphere is the ozone layer.
The ozone layer is one of those secondary atmospheric layers mentioned above. The ozone layer is what protects the Earth from most of the ultraviolet rays coming from the Sun. If you’ve ever looked at bottles of sunscreen lotion, you’ve probably heard of UV-A and UV-B, but how about UV-C? If not, it may be because 100% of the Sun’s UV-C light is absorbed by the ozone layer … which is fantastically great because UV-C is colossally harmful to all living things! Plus, the ozone layer absorbs the majority of UV-A and UV-B rays—but it’s still a good idea to put on sunscreen if you’re going to be outside in the sunlight. … So, yeah. That’s why the Earth’s ozone layer is so important.
3 = Mesosphere. The mesosphere layer starts where the stratosphere ends, about 31 miles (50 kilometers) up and extends to approximately 50 miles (or 80 kilometers) high. If you’re lucky enough to catch a glimpse of a fiery meteor headed toward Earth, you’re most likely looking into the mesosphere because the mesosphere is where most meteors burn up. Water vapor is scarce here, but the small amount of water vapor found is in the mesosphere’s noctilucent clouds, which are the highest clouds possible. The mesosphere is extremely cold, getting progressively colder the higher up within it you go, with the top of the mesosphere on average measuring -120° Fahrenheit (or -85° Celsius). Brrr!!!
4 = Thermosphere. Above the mesosphere, lies the thermosphere, which starts at about 50 miles (or 80 kilometers) up and reaches to approximately 440 miles (or 700 kilometers) above the Earth’s surface. Temperatures in the thermosphere begin to get warmer and increase the higher up you go because of the extremely low density of molecules contained in the thermosphere. In fact, there’s not enough molecules to produce clouds or even water vapor here. If you’ve ever seen the aurora borealis or aurora australis, you could be looking into the thermosphere because they are sometime seen here. … And if you’ve ever viewed the International Space Station as it orbits the Earth, you’ve definitely looked into the thermosphere as this is where the ISS is located.
The thermosphere also contains another secondary layer known as the ionosphere. Technically, the ionosphere can overlap the mesosphere, the thermosphere, and the exosphere as it is constantly shrinking and expanding depending on how much energy from the sun it happens to be absorbing. Gases in the ionosphere form ions when they’re excited by the Sun’s solar radiation; thus the name, ionosphere. And those auroras? It’s the ionsphere atoms interacting with the aurora’s high-energy particles that produce those beautiful lights in the sky.
5 = Exosphere. The exosphere is the highest of Earth’s atmospheric layers, extending from about 440 miles (700 kilometers) to 6,200 miles (10,000 kilometers) high and merging with the solar wind at its very top. Because the molecules found here are of such low density, the exosphere doesn’t behave like a gas, so particles can escape into space. The aurora borealis and aurora australis mentioned above will appear in the lowest part of the exosphere if they don’t appear in the thermosphere. And if you depend on a satellite signal for anything, it’s most likely being transmitted to Earth from the exosphere as this is where most satellites orbit the Earth.
… If you’re having trouble deciding where our planet stops and outer space begins, you’re not alone. Even the majority of scientists use what’s known as the Karman line to denote where Earth’s atmosphere ends and outer space starts. (FYI, the Karman line is an imaginary line drawn around the Earth 62 miles (or 100 kilometers) above the surface, set here because traditional aircraft cannot fly above it because 99.99997% of Earth’s atmosphere is under the line. Hence, the reasoning that the minute amount of atmosphere above could be considered outer space.)
So the next time you’re outside, take a moment to look up and breathe in some atmosphere! 🙂