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The Earth’s Atmosphere

Nowhere on Earth is truly empty. If you reach out in front of yourself now, your hand will come into contact with billions of atoms. That’s because our planet is rich with gaseous air. Invisible to us, this air is part of the atmosphere. The atmosphere is a layer of gases surrounding our world. It’s extremely important to life on Earth.
An image of Earth's atmosphere from the air. You can see the curve of the Earth on the horizon.

Composition of the Atmosphere

At all times, we’re surrounded by certain gases. A few, in particular, saturate the air.
The most common is nitrogen gas. It makes up 78% of the atmosphere. Notably, most living things need nitrogen, but few can use it as a gas. Special bacteria help convert it into a soil chemical. The next most common gas in our atmosphere is oxygen (21% of our atmosphere). Its importance is pretty clear to us.
The remainder of the gases in our atmosphere come in very small amounts. After oxygen is argon, which makes up only 0.9% of the air around us. Everything else is pretty rare.
Although, that doesn’t mean the remaining gases aren’t important. Carbon dioxide, another atmospheric gas, helps to keep our planet warm. Additionally, some polluting gases (which we put there) have negative ecological effects. An example would be acid rain.


An image of a factory surrounded by smog.

Pollution adds new, harmful gases to our atmosphere. I want to breathe oxygen, not this stuff!

Notably, we’re still forgetting one major gas: water vapor. Water vapor can actually compose up to 5% of our atmosphere! Yet, we don’t usually include it in our count. That’s because its concentration varies so widely. In some places, there is basically no water vapor at all.

Why do We Have an Atmosphere?

The atmosphere is a bunch of gases floating around a rocky planet in space. So, why don’t they all just float away? The answer is gravity. While not every planet has an atmosphere, ours is a dense one. This gives it an especially strong gravitational pull. Tiny gas molecules have a hard time escaping.

Layers of the Atmosphere

We can’t see the atmosphere, aside from its blue hue. And yet, it’s actually very complex. It’s composed of 5 unique layers which span hundreds of miles! We’ll look over each of these next.

An illustration showing the layers of Earth's atmosphere.

The different layers of the atmosphere.

Troposphere (Ground to 11 Miles Up)

The troposphere is the first layer of the atmosphere (where we live). It’s also where most of the gas and water vapor are at. Interestingly, this is what causes weather. Air, heat, and water flow throughout the troposphere constantly. This produces all sorts of weather events.

Stratosphere (11 Miles to 31 Miles Up)

The stratosphere is the second atmospheric layer. Its most notable feature is that it contains the ozone layer. This is a thin band of a gas called ozone. It’s important because it blocks dangerous UV radiation from reaching Earth’s surface.
Another thing about the stratosphere is that temperatures changes are inverted. This means that things get warmer as we go up. It’s the opposite of how things work in the troposphere. The reason for this is that the ozone layer soaks up a lot of radiation. It then releases the energy as heat, which rises up into the stratosphere.

Mesosphere (31 Miles to 50 Miles Up)

The mesosphere is the third atmospheric layer. There, temperature changes are inverted again. This makes the top of the mesosphere the coldest place in our atmosphere.

Thermosphere (50 Miles to 375 Miles Up)

The thermosphere is, per its name, an extremely hot layer. The gases in it absorb and radiate lots of energy. As a result, temperatures there can reach up to 4,500 degrees Fahrenheit. Spacecraft have to protect against this if they are to make it safely into space.

Exosphere (375 Miles and Beyond)

The last layer of our atmosphere is the exosphere. The exosphere is hardly a layer at all. In fact, it doesn’t even have an end. The few gases in it just blend smoothly into space.

An image of Earth's atmosphere from space.

Earth’s atmosphere as seen from the ISS. It blends smoothly into the space surrounding our planet.

Other Great Resources:

All About the Atmosphere – Geography4Kids: http://www.geography4kids.com/files/atm_intro.html

How Mars Lost Its Atmosphere, and Why Earth Didn’t: https://www.washingtonpost.com/news/speaking-of-science/wp/2017/03/30/how-mars-lost-its-atmosphere-and-why-earth-didnt/?utm_term=.f81d6741da36

(Video) Bozeman Science on Earth’s Atmosphere: https://www.youtube.com/watch?v=6LkmD6B2ncs

(Video) Where Does Space Start? – Astrum: https://www.youtube.com/watch?v=JrGuomu9NGY


Written by: Noah Louis-Ferdinand