Roughly what share of the atmosphere's dry air is nitrogen?
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Earth & Space Science · Foundations
Atmosphere
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In 30 seconds
The Atmosphere The envelope of gas held around Earth by gravity, made up mostly of nitrogen and oxygen. Full entry → is a layered envelope of gas held to Earth by gravity. By volume, dry air is roughly 78 percent nitrogen and 21 percent oxygen, with argon, carbon dioxide, and other trace gases making up the rest. Five layers stack from the ground up: Troposphere The lowest layer of the atmosphere, from the surface to roughly 6-20 kilometers, where nearly all weather occurs. Full entry →, Stratosphere The layer above the troposphere, from the top of the troposphere (about 6-20 kilometers, depending on latitude) to about 50 kilometers, where the ozone layer absorbs ultraviolet radiation. Full entry →, Mesosphere The middle layer of the atmosphere, from about 50 to 85 kilometers, where most meteors burn up on entry. Full entry →, Thermosphere The layer from about 85 to 600 kilometers where temperature rises with height and auroras occur. Full entry →, and Exosphere The outermost layer of the atmosphere, from about 600 to 10,000 kilometers, where atoms can escape into space. Full entry →. Air pressure The force exerted by the weight of the air above a point; it decreases with altitude. Full entry → falls with altitude — about half of the atmosphere lies below 5.6 kilometers. Greenhouse gases absorb and re-emit heat, keeping the surface warm, while the whole envelope shields life from solar radiation and meteors.
Why this matters
Every breath you take draws from the same thin shell of gas that protects the planet, and knowing its structure explains much of what you see in the sky and in a forecast. The layers tell you where weather forms, where jets fly, where meteors vanish, and where satellites circle. Composition explains what the air is made of and why greenhouse gases matter for surface temperature. The pressure-altitude rule is why mountain climbers need supplemental oxygen and why airplane cabins are pressurized. Because the atmosphere is the medium through which we observe everything from weather to starlight, reading it carefully is a foundation for earth science, environmental science, and everyday scientific literacy.
The college version
What the air is made of
The atmosphere is the envelope of gas that surrounds Earth, held in place by gravity. A useful way to describe it is by composition: what the air is made of. In dry air — air with the water vapor removed — nitrogen is by far the most abundant gas, making up about 78 percent of the volume. Oxygen comes next at about 21 percent. Together these two gases account for roughly 99 percent of dry air. The remaining share is a mix of argon (about 0.9 percent), carbon dioxide (about 0.04 percent), and a collection of trace gases such as neon, helium, and methane. Water vapor is a separate, variable ingredient: in the lowest layers it can range from near zero to about 4 percent, which is why forecasts speak of humidity rather than a fixed water content. These percentages are approximate — NOAA reports them as 78.084 percent nitrogen, 20.946 percent oxygen, 0.934 percent argon, and roughly 0.042 percent carbon dioxide — and the exact values shift slightly with time, place, and measurement. For most purposes, about 78 percent nitrogen and about 21 percent oxygen captures the air we breathe.
The five layers
Temperature, not distance, is the main ruler scientists use to divide the atmosphere. From the ground up, five layers are recognized: troposphere, stratosphere, mesosphere, thermosphere, and exosphere, each bounded by a pause where properties change fastest. The troposphere is the lowest layer, reaching from the surface to roughly 6-20 kilometers depending on latitude and season; it holds most of the atmosphere's mass and is where nearly all weather happens. Above it, the stratosphere extends from the top of the troposphere — about 6 to 20 kilometers, depending on latitude — up to about 50 kilometers. Temperature rises with height there because the Ozone layer A region of the stratosphere with a higher concentration of ozone gas that absorbs most of the Sun's ultraviolet radiation. Full entry → absorbs ultraviolet radiation from the Sun — the same absorption that protects life on the surface. The stratosphere holds about 19 percent of the atmosphere's gases, which is why commercial jets cruise near its base, above the weather. The mesosphere, from about 50 to 85 kilometers, is where incoming meteors slow down and burn up, leaving the streaks we call shooting stars. Above it, the thermosphere spans roughly 85 to 600 kilometers; temperatures there climb with height, reaching about 2,000 degrees Celsius near the top, though the air is far too thin to feel hot. Auroras flicker in this layer. Finally, the exosphere extends from about 600 to 10,000 kilometers, a gradual fade into space where individual atoms can escape and many satellites orbit. These boundaries are approximate and shift with conditions; they are markers on a continuous change, not walls.
Pressure thins with height
Air pressure is the weight of the air above a point, and it decreases steadily as you climb, because there is simply less air overhead. The fall is fastest near the ground and gentler higher up. A vivid benchmark comes from NOAA: although the atmosphere extends hundreds of kilometers upward, about half of all its gas lies within the first 5.6 kilometers (about 18,000 feet) above sea level. This is why high mountains demand supplemental oxygen, why airplane cabins are pressurized, and why the standard sea-level pressure of about 1013 hectopascals drops to roughly half that value by 5.6 kilometers. The same principle explains the thin air climbers describe: each breath at altitude contains fewer molecules, including fewer oxygen molecules. Pressure differences also set the atmosphere in motion — the wind — but the patterns of those pressure systems are the subject of a separate lesson; here, the principle is simply that altitude removes weight.
Greenhouse gases and the atmosphere's work
Some gases in the atmosphere — water vapor, carbon dioxide, methane, nitrous oxide, and ozone — are greenhouse gases. They behave differently from nitrogen and oxygen: they let sunlight pass through, but they absorb the infrared radiation that the warmed surface radiates back out, and they re-emit some of it toward the ground. That re-radiated heat keeps the lower atmosphere warmer than it would otherwise be. This natural Greenhouse effect The warming of the lower atmosphere caused by greenhouse gases absorbing and re-emitting infrared radiation. Full entry → is not a flaw; without it, Earth would be far too cold for life as we know it. The atmosphere does several other jobs at once. Its ozone layer absorbs most of the Sun's harmful ultraviolet radiation before it reaches the surface. Its gases burn up most incoming meteors. It supplies the oxygen organisms breathe and the carbon dioxide plants use, and it transports water vapor through the water cycle. The atmosphere is not a passive wrapper — it is an active, layered system that makes the surface habitable. How weather systems move within it, how it exchanges heat with the oceans, and how its greenhouse balance is changing are each topics of their own lessons.
Eli explains
The same idea, in plain words
Explain it like I’m 10
Earth wears an invisible coat of gas, and you live at the bottom of it. That coat is the atmosphere. The air you breathe is mostly nitrogen — about 78 percent — with oxygen at about 21 percent and small amounts of argon, carbon dioxide, and other gases mixed in. The coat has five layers, like floors in a building. The troposphere holds the weather. The stratosphere carries the ozone layer, which blocks most of the Sun's ultraviolet light, and planes fly there to get above the weather. The mesosphere burns up most meteors. The thermosphere is where auroras glow, and the exosphere gradually fades into space, where atoms drift away and satellites orbit. The higher you go, the thinner the air: about half of the whole atmosphere lies below 5.6 kilometers. And a few gases — water vapor, carbon dioxide, methane — act like a blanket, holding in heat and keeping the planet warm enough for life.
Picture it like this
Think of the atmosphere as Earth's sleeping bag. The fabric traps some of your body heat so you stay warm, and it shields you from wind and weather. The atmosphere does the same: greenhouse gases trap heat from the ground, the ozone layer blocks harsh sunlight, and the mesosphere burns up space rocks before they can reach you.
Where the picture stops working
A sleeping bag is one even layer, but the atmosphere has five distinct layers that behave differently, and temperature rises in some of them while falling in others. A sleeping bag sits still, while the atmosphere is a moving fluid whose gases circulate, mix, and exchange heat with the surface.
Worked example
Take an imaginary elevator ride from the beach up through the atmosphere. At sea level, the full weight of the air presses down, and a barometer reads about 1013 hectopascals. By 5.6 kilometers, about half of the atmosphere lies below you, so the pressure is roughly half the sea-level value — the same rule that forces climbers on high peaks to carry supplemental oxygen. Near 12 kilometers you pass the tropopause, the top of the troposphere, where commercial jets cruise above nearly all weather. Between 20 and 50 kilometers, the ozone layer absorbs ultraviolet light and temperature rises with height. Around 70 kilometers, a small meteor streaks past and burns up in the mesosphere. Far above, at roughly 400 kilometers, the International Space Station circles inside the thermosphere, where temperatures climb toward 2,000 degrees Celsius even though the air is far too thin to feel hot.
Key takeaway
Earth's atmosphere is a layered envelope of gas, mostly nitrogen and oxygen, whose pressure thins with altitude; its layers, greenhouse gases, and shields together make the planet habitable.
Quick check
3 questions here, of 5 in this lesson’s practice set. Answers stay hidden until you check.
In which layer of the atmosphere do most meteors burn up?
Choose an answer, then check it.
A commercial jet cruises where the air is thin, weather is rare, and ozone absorbs ultraviolet radiation, warming the layer with height. Which layer is this?
Choose an answer, then check it.
Study tools & related lessonsYou’ll learn to · Common mistakes · Easily confused · Key vocabulary · Related
You’ll learn to
- Define the atmosphere and describe its approximate composition by volume, naming nitrogen, oxygen, argon, carbon dioxide, and variable water vapor.
- Identify the five main layers of the atmosphere in order and state at least one key feature of each.
- Explain why air pressure decreases with altitude, including the rule that about half of the atmosphere lies within the first 5.6 kilometers.
- Explain how greenhouse gases warm the lower atmosphere and why the natural greenhouse effect matters.
- Describe the atmosphere's protective functions, including shielding the surface from harmful radiation and burning up meteors.
Common mistakes
Thinking the atmosphere ends at a hard boundary.
Layers blend into one another through pauses, and the exosphere fades gradually into space by about 10,000 kilometers; there is no wall at the top.
Assuming temperature always drops as you climb.
Temperature falls in the troposphere and mesosphere, but it rises in the stratosphere, where ozone absorbs ultraviolet light, and in the thermosphere, where high-energy solar radiation is absorbed.
Concluding the thermosphere must feel blazing hot because its temperature reaches about 2,000 degrees Celsius.
Temperature measures the energy of individual molecules; with so few molecules present, almost no heat reaches your skin, and the layer would feel very cold.
Believing oxygen is the most abundant gas in the atmosphere.
Nitrogen makes up about 78 percent of dry air and oxygen about 21 percent; oxygen is second, not first.
Treating greenhouse gases as purely harmful.
Water vapor and carbon dioxide occur naturally, and the greenhouse effect they create keeps Earth warm enough for life; how human activity is changing that balance is the subject of a separate lesson on climate change.
Easily confused
Troposphere vs. Stratosphere
The troposphere holds nearly all weather and cools with height; the stratosphere above it is stable, holds the ozone layer, and warms with height.
Mesosphere vs. Thermosphere
Meteors burn up in the mesosphere and temperatures fall with height; auroras glow in the thermosphere, where temperatures rise toward about 2,000 degrees Celsius.
Nitrogen vs. Oxygen
Nitrogen is the most abundant gas in dry air at about 78 percent; oxygen follows at about 21 percent, and together they make up roughly 99 percent.
Natural greenhouse effect vs. Climate change
The natural greenhouse effect, driven by water vapor, carbon dioxide, and other gases, keeps the planet warm enough for life; climate change — how that balance is shifting — is a separate sibling topic.
Key vocabulary
- Atmosphere
- The envelope of gas held around Earth by gravity, made up mostly of nitrogen and oxygen.
- Troposphere
- The lowest layer of the atmosphere, from the surface to roughly 6-20 kilometers, where nearly all weather occurs.
- Stratosphere
- The layer above the troposphere, from the top of the troposphere (about 6-20 kilometers, depending on latitude) to about 50 kilometers, where the ozone layer absorbs ultraviolet radiation.
- Mesosphere
- The middle layer of the atmosphere, from about 50 to 85 kilometers, where most meteors burn up on entry.
- Thermosphere
- The layer from about 85 to 600 kilometers where temperature rises with height and auroras occur.
- Exosphere
- The outermost layer of the atmosphere, from about 600 to 10,000 kilometers, where atoms can escape into space.
- Ozone layer
- A region of the stratosphere with a higher concentration of ozone gas that absorbs most of the Sun's ultraviolet radiation.
- Greenhouse gas
- A gas such as carbon dioxide or water vapor that absorbs infrared radiation and re-emits some of it, warming the lower atmosphere.
- Greenhouse effect
- The warming of the lower atmosphere caused by greenhouse gases absorbing and re-emitting infrared radiation.
- Air pressure
- The force exerted by the weight of the air above a point; it decreases with altitude.
Sources & references
- JetStream: The Atmosphere — NOAA National Weather Service JetStream (Online School for Weather)
- JetStream: Layers of the Atmosphere — NOAA National Weather Service JetStream (Online School for Weather)
- JetStream: Air Pressure — NOAA National Weather Service JetStream (Online School for Weather)
- Basics of the Carbon Cycle: Glossary Terms — NOAA Global Monitoring Laboratory
- Earth Facts (NASA Science, Solar System Exploration) — NASA
EliExplains lessons are original prose written from the open, credible references above. See Copyright & Licensing.
Researched 2026-08-21
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