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Moon seen through the atmosphere. Image credit: NASA

Composition of the Earth’s Atmosphere

9 Mar , 2009


Breathe in and you can appreciate that the Earth’s atmosphere has everything needed to support life on Earth. But what’s in it? Let’s take a look at the composition of the Earth’s atmosphere. Of course, things haven’t always been balanced they way they are today. But more of that in a second.

The Earth’s atmosphere is composed of the following molecules: nitrogen (78%), oxygen (21%), argon (1%), and then trace amounts of carbon dioxide, neon, helium, methane, krypton, hydrogen, nitrous oxide, xenon, ozone, iodine, carbon monoxide, and ammonia. Lower altitudes also have quantities of water vapor.

The atmosphere we have today is very different from the Earth’s early atmosphere. When the planet first cooled down 4.4 billion years ago, volcanos spewed out steam, carbon dioxide and ammonia, and it was 100 times as dense as today’s atmosphere.

The earliest bacteria, known as cyanobacteria, were probably the first oxygen-producing organisms on Earth. Approximately 2.7 to 2.2 billion years ago, they released large amounts of oxygen and sequestered the carbon dioxide. As oxygen was released, it reacted with ammonia to release nitrogen. The carbon dioxide in the atmosphere is exhaled by plants (and produced by human industry burning fossil fuels).

We have written many articles about the Earth for Universe Today. Here’s an article about how the Earth’s atmosphere is slowly leaking into space, and here’s an article about how the early Earth’s atmosphere was similar to Titan’s atmosphere.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

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