Send a probe straight up, from the ground to 1,000 km. At every height it reads the temperature, the air pressure, the air density and how much of all the air is below it. Use the slider, the step buttons or tap the column; or take the guided tour. Then predict the answers to 3 questions and check them with the probe. Mission: all 3 answered, at least 2 right on the first try.
The column is to scale from 0 to 120 km. Above the zigzag marks the scale is squeezed: 120–600 km, then the exosphere up to about 10,000 km.
Model: US Standard Atmosphere 1976, the average state of the air at middle latitudes. From 0 to 86 km the page uses its exact layer formulas; above 86 km it uses the 1976 table (moderate Sun activity). Real air changes with the weather, the season and the latitude. The model’s tropopause is at 11 km; most books round it to about 12 km (about 8 km near the poles, 16–18 km near the equator). The stratosphere starts at about 12 km, but in the model the temperature stays flat at −56.5 °C from 11 to about 20 km; the warming begins above about 20 km. The mesopause, about 85–90 km, is the top of the mesosphere and the coldest air (about −86 °C). Pressure: 1 hPa (hectopascal) = 1 millibar; sea level is 1,013.25 hPa.
Put the names in the right places. Press a label, then press the place where it belongs (no dragging needed; the keyboard works too). Basic: the 5 layers. Advanced: the 5 layers plus the 4 lines between them. The first check of each round counts. Mission: Basic 5 / 5, or Advanced at least 8 / 9.
The layers are defined by how the temperature changes; their names come from Greek and Latin roots: tropo- means “turning” (the air mixes and churns), strato- “layered” (calm layers), meso- “middle”, thermo- “heat” and exo- “outside”. Each boundary takes the name of the layer below it plus -pause. The Kármán line is not a temperature boundary: it is a common agreed edge of space (US agencies such as NASA and the FAA use 80 km, 50 miles).
The classic atmosphere lab, done with real data. Step 1: record at least 10 altitudes from the ground to at least 100 km (tap an altitude, or record where the probe in Mission 1 is). The graph shows temperature across and altitude up, the way textbooks draw it. Step 2: set the three boundaries where the line changes direction, then answer one question. Mission: 10 points, 3 boundaries right on the first check of an attempt, and the question right on the first try.
| Altitude (km) | Temperature (°C) | Pressure (hPa) |
|---|
Boundaries count as right within: tropopause 10–20 km (in the model the temperature stays flat at −56.5 °C from 11 to 20 km, then starts rising, so the turn can look anywhere in that range), stratopause 47–53 km, mesopause 80–90 km. Only the first check of each attempt counts; hints appear after it. Real soundings wiggle more than this smooth average; a teacher can print the worksheet table (For Teachers) to graph by hand.
Sunlight is a mix: visible light passes through the air and warms the ground; ultraviolet (UV) is absorbed by ozone in the stratosphere; X-rays and extreme UV are absorbed by oxygen and nitrogen high in the thermosphere. Wherever light is absorbed, the air gets warmer. Switch the ozone off, or change the Sun, and watch the model profile (orange) move away from the real one (gray). Then match each warm zone to its cause and explain the stratosphere. Mission: 3 matches and a claim–evidence–reasoning answer with at least 2 parts right on the first try.
A simplified model: “ozone off” removes the ozone heating, so the stratosphere stays near −60 °C; the Sun buttons set the top of the thermosphere to about 500, 727 or 1,500 °C. Everything else is the standard atmosphere.
Distance does not explain it: Earth is about 150 million km from the Sun, so 50 km higher is 0.00003 % closer. What matters is which gas absorbs which kind of light. Ozone (O₃) is at most about 10 molecules in every million, but it absorbs almost all UV-C and most UV-B, which also protects living things on the ground. More on the kinds of light: electromagnetic spectrum.
Every day, weather services launch more than a thousand balloons that carry instruments up through the troposphere into the stratosphere. A latex balloon about 1.8 m wide at launch keeps growing as it rises, until it bursts and the instruments fall back on a parachute. Choose a balloon and a payload, predict the burst height, then launch. Mission: launch 2 different balloons (with a prediction each time) and answer 2 questions right on the first try.
| Altitude (km) | Pressure (hPa) | Temperature (°C) | Balloon width (m) | Snack bag |
|---|
The gas inside stays at about the outside pressure and temperature, so its volume follows V/V₀ = (P₀/P)(T/T₀) and the width grows with the cube root of the volume. At 30 km the volume is about 67 times the launch volume: a 1.8 m balloon is about 7.3 m wide. Real balloons usually burst at 30–35 km. The snack bag is sealed and half full of air at launch: it is tight at twice its launch volume and its seams split at 3 times. The same thing puffs up chip bags on a mountain road. The gas law behind it: gas laws.
Take a 1-liter sample of air at six places. Each dot stands for the same number of real particles (about 10²⁰), so you can compare how crowded the air is. The readout gives the real count, the oxygen share and how much oxygen one breath would hold. Mission: samples from at least 4 places and 3 questions answered, at least 2 right on the first try.
Particle counts: n = P / (kT), from the model’s pressure and temperature (k = 1.38 × 10⁻²³ J/K). Sea level: about 2.5 × 10²² particles in a liter. Above about 100 km the gases no longer stay mixed: at 300 km most particles are single oxygen atoms (O), made when UV splits O₂. At 300 km the readout gives rounded values (mostly, about 80–90 %, single O atoms). Water vapor shown near the ground is a typical value; it ranges from almost 0 % in cold, dry air to about 4 % in the warm, humid tropics. Particle speed and temperature: kinetic theory of gases.
Press a card, then press the layer where it belongs. Only your first placement counts, and each card shows its reason. Mission: at least 11 of 14 right.
10 questions from a bank of 20. Score 7 or more to complete the mission. Each new round picks new questions in a new order.
Air has weight. The air above every square centimeter of sea level weighs about 1 kg, which presses about 10 newtons on that square centimeter: that is air pressure, 1,013 hPa. The higher you go, the less air is above you, so the pressure drops. It roughly halves every 5.5 km. That is why half of all the air is below 5.5 km, about 90 % is below 16 km and 99 % is below about 31 km. If Earth were an apple, the 99 % of the air below about 31 km would be thinner than its skin (about 0.2 mm); the last thin traces fade out far beyond that.
Scientists split the atmosphere where the temperature trend changes. Going up, the temperature falls, rises, falls and rises again: a zigzag. Each turning point is a boundary, named after the layer below it plus -pause: tropopause, stratopause, mesopause. The mix of gases stays almost the same up to about 80–100 km.
We live here, and almost all weather happens here, because almost all the water vapor is here. Sunlight passes through the air and warms the ground; the ground warms the air from below, so it is warmest at the bottom. On average the temperature drops about 6.5 °C for every kilometer you go up. The troposphere holds about three quarters of all the air. It is about 8 km thick at the poles and 16–18 km at the equator.
The ozone layer is here. Ozone (O₃) absorbs ultraviolet (UV) light from the Sun. The absorbed energy makes the air molecules move faster. At the bottom of the stratosphere the temperature stays about −56 °C up to about 20 km; above that it rises with height, to about −3 °C at the top. Warm air above cool air does not churn, so the stratosphere is calm and dry. Weather balloons and some research planes fly here.
Above the ozone layer there is little to absorb sunlight, so the temperature falls again, down to about −86 to −90 °C at the mesopause (about 85–90 km, the top of the mesosphere): the coldest place around Earth. The air is very thin, but there is still enough of it to heat meteors until they glow and burn up. The highest clouds, noctilucent (night-shining) clouds of ice, form near the top.
The few particles in the thermosphere absorb X-rays and extreme UV, so they become very hot: 500 to 2,000 °C, depending on how active the Sun is. But there are so few of them that a thermometer would read very cold: they carry very little heat. Auroras glow here, and the International Space Station orbits here at about 410 km. Above about 600 km the exosphere slowly fades into space; particles rarely collide, and some light atoms escape. There is no sharp edge: the Kármán line at 100 km is a common agreed edge of space (US agencies use 80 km, 50 miles).
In Mission 1, compare 15 km and 30 km: it is warmer higher up. In Mission 4, switch the ozone off and watch the warm stratosphere disappear. In Mission 6, compare a breath at sea level and on Mt Everest: same 21 % oxygen, but only about one third of the molecules.
| Layer | Height | Temperature with height | Temperature | Key facts |
|---|---|---|---|---|
| Exosphere | about 600 to 10,000 km | about the same | very hot particles, almost no air | fades into space; polar weather satellites (about 800 km) |
| Thermosphere | about 85–90 to 600 km | rises ↑ | about −90 °C to 500–2,000 °C | X-rays and extreme UV absorbed; aurora; ISS (410 km); Hubble (about 500 km, slowly sinking); ionosphere |
| Mesosphere | about 50 to 85–90 km | falls ↓ | about −3 °C to about −86 °C at the mesopause (coldest) | most meteors burn up; noctilucent clouds |
| Stratosphere | about 12 to 50 km | about the same to 20 km, then rises ↑ | about −56 °C to −3 °C | ozone layer (most at 20–25 km) absorbs UV; weather balloons burst at 30–35 km |
| Troposphere | 0 to about 12 km | falls ↓ (6.5 °C per km) | 15 °C to about −56 °C | weather, clouds, almost all water vapor; 75–80 % of the air; airliners at 9–12 km |
Tropopause about 12 km (8 km at the poles, 16–18 km at the equator; 11 km in the standard atmosphere, with flat temperature up to 20 km) · Stratopause about 50 km · Mesopause about 85–90 km (the coldest air) · Kármán line 100 km (agreed edge of space; US agencies use 80 km) · Exobase (thermopause) about 500–1,000 km.
Related pages: weather and climate, severe weather, greenhouse effect, carbon cycle, electromagnetic spectrum (UV), kinetic theory of gases, gas laws, layers of the Earth.
Each thin slab of air must hold up the weight of the air above it: dP = −ρg dz. With the ideal gas law ρ = PM/(RT), this gives dP/P = −dz/H, where the scale height H = RT/(Mg). If the temperature were constant, P = P₀e−z/H: the pressure would drop by a factor e (2.718) every H kilometers. At 250 K, H ≈ 7.3 km, so the pressure halves every H ln 2 ≈ 5–6 km. Try it, and compare with the standard atmosphere, whose temperature changes with height:
Rising air expands because the pressure around it drops, and expanding air cools. Dry air cools at g/cp ≈ 9.8 °C per km (the dry adiabatic lapse rate). Moist air cools more slowly, about 5–6 °C per km, because condensing water vapor releases heat. The average troposphere, 6.5 °C per km, lies in between. Where the real temperature falls faster than the rising air cools, the air is unstable and thunderstorms can grow; an inversion (temperature rising with height) is very stable. The stratosphere is very stable: in the standard atmosphere it is isothermal from 11 to 20 km and then an inversion up to about 50 km, which is why storm tops spread out at the tropopause.
The tropopause is about 8 km high over the poles, 11–12 km at middle latitudes and 16–18 km over the equator, where strong heating and convection lift it. Over the tropics it is also the coldest (about −80 °C), which freeze-dries air entering the stratosphere. Jet streams blow near the tropopause, at about 9–16 km, where the tropopause height changes sharply.
(1) UV-C splits an oxygen molecule: O₂ + UV → O + O. (2) A free oxygen atom joins a molecule: O + O₂ → O₃ (a third molecule carries away the extra energy). (3) Ozone absorbs UV-B or UV-C and splits: O₃ + UV → O₂ + O. (4) O + O₃ → 2 O₂ removes ozone. Steps 2 and 3 repeat again and again: each time, UV energy turns into heat. That is the heating in Mission 4. Chlorine and bromine atoms from CFCs and halons speed up the destruction, especially on polar stratospheric clouds over Antarctica in spring: the ozone hole.
Signed in 1987 and later made stronger, the Montreal Protocol phased out CFCs and most other ozone-depleting chemicals; every country in the United Nations has joined it. The 2022 WMO/UNEP scientific assessment expects ozone to return to its 1980 values around 2040 for most of the world, around 2045 over the Arctic and around 2066 over Antarctica. The ozone hole and global warming are different problems, but they are linked: CFCs are also strong greenhouse gases, so the protocol has also slowed warming (see greenhouse effect).
X-rays and extreme UV do more than heat the thermosphere: they knock electrons off atoms and molecules. From about 60 to 1,000 km these free electrons and ions form the ionosphere, which overlaps the upper mesosphere and the thermosphere. It reflects some radio waves (shortwave radio can bounce around the world), it changes between day and night and it disturbs GPS signals during solar storms. Auroras happen when charged particles from the Sun, guided by Earth’s magnetic field, hit oxygen (green and red light) and nitrogen (blue and purple light) at about 100–300 km.
Standards: Georgia S6E4a (compare and contrast the composition of Earth’s atmospheric layers, including the ozone layer: Missions 1, 2, 4, 6, 7), Florida SC.6.E.7.9 (how the composition and structure of the atmosphere protects life and insulates the planet: Missions 4, 6), South Carolina 6-4.1 (compare the composition and structure of the atmospheric layers: Missions 1–3, 6). Supports NGSS MS-ESS2-6 (unequal heating and circulation), MS-PS1-4 (particle motion, temperature and pressure: Missions 5, 6) and, in Going further, HS-ESS2-4 (energy flow and feedbacks). NGSS has no performance expectation that names the layers, so treat those as supporting links. Objective: students use real standard-atmosphere data to describe how temperature and pressure change with height, name and order the five layers by their temperature trends, and explain the warm stratosphere with ozone absorbing UV.
Differentiation. Support: start with the guided tour, use Basic labels, record the altitude buttons 0, 10, 20 … 120 in order in Mission 3, and give the sentence frame “The stratosphere is warmer at the top because ____ absorbs ____.” Extension: Advanced labels, the scale-height calculator and the Chapman cycle in Going further, and the latitude question “Why is the tropopause higher over the equator?” Language support: the vocabulary list below and the word roots under Mission 2. Misconceptions to target: colder all the way up; higher means closer to the Sun; the thermosphere would burn you; less oxygen percent on mountains; a sharp edge to space; the ozone hole causes global warming. Missions are saved on the student’s device; the certificate prints as proof of completion.
From the ground up: the troposphere (0 to about 12 km), the stratosphere (about 12 to 50 km), the mesosphere (about 50 to 85–90 km), the thermosphere (about 85–90 to 600 km) and the exosphere (from about 600 km, fading into space at about 10,000 km). A memory sentence: “The Strong Man Thinks Easily.”
Key takeaway: troposphere, stratosphere, mesosphere, thermosphere, exosphere.By how the temperature changes with height. The temperature falls in the troposphere, rises in the stratosphere, falls in the mesosphere and rises in the thermosphere. The boundaries between the layers (tropopause, stratopause, mesopause) are where the trend changes direction.
Key takeaway: each layer has its own temperature trend; boundaries are the turning points.Because the ozone layer is there. Ozone absorbs ultraviolet (UV) light from the Sun, and the absorbed energy makes the air molecules move faster, so the air gets warmer. The stratosphere starts at about 12 km; the temperature stays about −56 °C up to about 20 km, then rises to about −3 °C at the top, because most of the UV is absorbed high up. Being closer to the Sun has nothing to do with it.
Key takeaway: ozone absorbs UV light and heats the stratosphere.The mesosphere. Its top, the mesopause at about 85–90 km, is about −86 to −90 °C on average, colder in summer over the poles. There is little ozone to absorb sunlight there, and the air is too thin to hold much heat.
Key takeaway: the mesosphere, about −90 °C at the mesopause.Temperature measures how fast particles move. In the thermosphere the few particles absorb X-rays and extreme UV and move very fast, so the temperature is 500 to 2,000 °C. But the air is so thin (at 300 km about 40 billion times fewer particles per liter than at sea level) that they hit you very rarely and carry almost no heat. A thermometer in the shade would read far below freezing.
Key takeaway: very fast particles, but far too few to heat you.There is no sharp edge: the air just keeps getting thinner. The Kármán line at 100 km is a common agreed edge of space (US agencies such as NASA and the FAA use 80 km, 50 miles). The exosphere still has a few particles out to about 10,000 km, and some light atoms escape into space from there.
Key takeaway: no sharp edge; 100 km (the Kármán line) is a convention.Airliners cruise at about 9–12 km (31,000–39,000 feet), near the top of the troposphere, above most clouds and weather. Some research planes fly higher, at about 20 km, in the lower stratosphere. Weather balloons rise to about 30–35 km before they burst.
Key takeaway: airliners: top of the troposphere; balloons: stratosphere.The air is thinner. On top of Mt Everest (8.8 km) the air pressure is only about 31 % of sea level. The air is still about 21 % oxygen, but each breath holds only about one third as many oxygen molecules, so climbers use bottled oxygen.
Key takeaway: same 21 % oxygen, but only about ⅓ the molecules per breath.About 75 to 80 %, because air pressure (the weight of the air above) halves about every 5.5 km. Half of all the air is below 5.5 km, about 90 % is below 16 km and 99 % is below about 31 km. Almost all the water vapor is in the troposphere too, which is why weather happens there.
Key takeaway: about three quarters of the air, and almost all the water vapor.It is the part of the stratosphere, about 15 to 35 km up, with the most ozone (O₃). Even there ozone is at most about 10 molecules in every million, but it absorbs almost all UV-C and most UV-B light, which would damage living cells. CFCs thinned it, especially over Antarctica; since the Montreal Protocol (1987) it is recovering and should be back to 1980 levels by about 2040–2066.
Key takeaway: ozone in the stratosphere blocks harmful UV and is slowly recovering.