The atmosphere is the layer of gases that surrounds our planet. It is thin (more than 99% of the air is in the bottom 50 km, but Earth is over 12,000 km wide), yet absolutely essential. The atmosphere gives us the oxygen we breathe, blocks dangerous radiation from the Sun, keeps the planet warm enough for life, and creates the weather. Without it, Earth would be a freezing, airless ball like the Moon. The atmosphere has five main layers stacked one on top of another, each with very different conditions.
- Five layersTroposphere, stratosphere, mesosphere, thermosphere, exosphere
- % nitrogenApprox. 78%The most common gas
- % oxygenApprox. 21%The gas we breathe
- % argonApprox. 0.9%Plus trace amounts of CO2 and others
- Troposphere heightApprox. 12 kmWhere almost all weather happens
- Top of atmosphereApprox. 10,000 kmFades gradually into space
The five layers
- Troposphere (0 to 12 km): the layer we live in. Contains almost all the weather and approx. 75% of the air. Gets colder with height.
- Stratosphere (12 to 50 km): contains the ozone layer, which absorbs harmful UV from the Sun. Where jets fly.
- Mesosphere (50 to 85 km): the coldest layer. Where most meteors burn up.
- Thermosphere (85 to 600 km): very thin, but extremely hot. Where the International Space Station orbits, and where the auroras (Northern and Southern Lights) appear.
- Exosphere (600 km and above): the outermost layer, slowly fading into the vacuum of space.
What air is made of
The air around you is a mixture of many gases.
- Nitrogen (approx. 78%): mostly unreactive, just sits there.
- Oxygen (approx. 21%): what we (and almost every other animal) breathe.
- Argon (approx. 0.9%): a noble gas, completely inert.
- Carbon dioxide (approx. 0.04%): a tiny percentage, but vital for plants, and rising due to human activity.
- Water vapour: varies a lot, from almost nothing in deserts to several percent in tropical rainforests.
- Traces of other gases: neon, helium, methane and many others.
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