Earth's Atmosphere & CO2
Describe the composition of Earth's atmosphere (mainly nitrogen and oxygen, with small amounts of CO₂ and other gases), explain how human activity increases CO₂, and describe the impact on global climate
What a learner can do afterwards
- States the approximate percentages of nitrogen, oxygen, CO₂, and argon in the atmosphere
- Explains how burning fossil fuels and deforestation increase atmospheric CO₂
- Describes the greenhouse effect and how it leads to climate change
- Discusses one specific consequence of climate change (e.g. rising sea levels, extreme weather)
1 · Read
Earth's atmosphere is the layer of gas wrapped around the planet, held in place by gravity. It looks empty, but it's a mix of several gases. Two of them make up almost all of it: nitrogen and oxygen.
About 78% of the air is nitrogen and about 21% is oxygen, the gas your body needs to survive. The last 1% is a mix of other gases. Almost all of that sliver is argon, and only a tiny part of it, about 0.04%, is carbon dioxide (CO2).
CO2 is less than half of that leftover sliver, yet it plays a huge part in keeping Earth warm. You already know CO2 traps heat near Earth's surface, the greenhouse effect. When people burn coal, oil, and gas for energy, and when they cut down forests that would otherwise soak up CO2, they add more of this gas to the air. More CO2 traps more heat, and Earth's average temperature climbs. That's climate change, and it's already causing sea levels to rise as ice melts and warmer water expands.
A gas doesn't need a big share of the air to matter. CO2 is a tiny slice of the atmosphere, but even small increases trap enough extra heat to shift climate patterns worldwide.
Air is mostly nitrogen and oxygen, but burning fuel and clearing forests keeps adding CO2, and that tiny gas is enough to trap extra heat and warm the whole planet.
More to read
8.3 Earth's Atmosphere
Earth's atmosphere is a mixture of gases held by gravity. Nitrogen makes up about 78%, oxygen about 21%, argon about 0.9%, and carbon dioxide about 0.04% (400 ppm). Trace gases include neon, helium, methane, and water vapour. The atmosphere has five layers based on temperature changes: troposphere (where weather happens), stratosphere (ozone layer), mesosphere, thermosphere, and exosphere. Weather is short-term conditions; climate is long-term patterns.
Key points: Earth's atmosphere
The atmosphere's composition is 78% nitrogen, 21% oxygen, and 1% other gases including water vapour, argon, and carbon dioxide. CO2 is a greenhouse gas: it lets sunlight in but traps heat radiating from Earth's surface. Human activities, especially burning fossil fuels and deforestation, have increased CO2 levels from about 280 ppm before the Industrial Revolution to over 420 ppm today. This enhanced greenhouse effect is warming the planet, causing rising sea levels, more extreme weather, and ecosystem disruption.
8.4 Life, Chemical Evolution, and Climate Change
Life and geological activity have shaped Earth's atmosphere over billions of years. Early Earth had no oxygen. Photosynthetic bacteria added oxygen, enabling complex life. The greenhouse effect keeps Earth habitable, but too much warming causes problems. Human activity is now the dominant force changing atmospheric composition. Burning fossil fuels releases CO2 that was locked away for millions of years. Deforestation reduces the planet's ability to absorb CO2. The result is climate change with impacts on weather patterns, sea levels, and ecosystems worldwide.
Carbon Dioxide Absorbs Infrared Energy
CO2 absorbs infrared energy radiated by Earth, trapping heat in the atmosphere. This greenhouse effect is natural and necessary, but human emissions are enhancing it. Even small temperature increases can have large consequences: melting ice, rising seas, shifting climate zones, more intense storms. The carbon cycle moves carbon between atmosphere, oceans, land, and living things. Human disruption of this cycle is the core of the climate challenge.
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Where it sits
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Where this leads
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8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.