The Atmosphere: Layers, Ozone and the Greenhouse Effect, Grade 9
Drawn to scale, the layer of air that holds every living thing is half a centimetre tall.
Grade 9 asks you to draw the atmosphere at 1 cm to 20 km. The thermosphere gets 17,5 cm. The troposphere, which contains all the weather, every bird, every aeroplane and everything that has ever lived, gets 0,5 cm.
This page covers the four layers and how to draw them properly, a greenhouse effect experiment you can actually measure with two jars and two thermometers, and why the ozone hole and global warming are two different problems.
The four layers
| Layer | From | To | What is there |
|---|---|---|---|
| Troposphere | Ground | About 10 km | All weather, all life, most aircraft. Holds over 70 % of the atmosphere's mass |
| Stratosphere | 10 km | About 50 km | The ozone layer, roughly 10 to 40 km up. Long distance flights cruise at the bottom of it |
| Mesosphere | 50 km | About 80 km | The coldest layer, about -90 °C. Meteors burn up here |
| Thermosphere | 80 km | About 350 km and beyond | Auroras. Very hot and so thin you would not feel it |
Where this fits in the curriculum
| Subject | Natural Sciences |
|---|---|
| Grade | 9 |
| Term | 4 |
| Strand | Planet Earth and beyond |
| Topic | Topic 19, The atmosphere |
| Status | Skills focus: drawing to scale. No assessed practical task |
| Marks | None prescribed. Our worksheet is 40 marks |
Drawing the atmosphere to scale
Scale: 1 cm represents 20 km.
| Layer | Top of the layer | On your page |
|---|---|---|
| Troposphere | 10 km | 0,5 cm |
| Stratosphere | 50 km | 2,5 cm |
| Mesosphere | 80 km | 4 cm |
| Thermosphere | 350 km | 17,5 cm |
Ask the class to guess first. Almost everybody expects the troposphere to be a third of the drawing. It is a twentieth of it, and the guess is what makes the answer stick.
The outdoor version, if you have a field
Scale: 1 metre represents 3,5 km. Pace out 100 m and the whole atmosphere fits on it.
| Feature | Where it falls |
|---|---|
| Top of the troposphere | 2,9 m from the start |
| Top of the stratosphere, and the ozone layer | 14,3 m |
| Top of the mesosphere | 22,9 m |
| The space station, 400 km up | 114 m, past the far end of the field |
Stand one learner at 2,9 m and tell the rest that everything alive is behind that person. Nothing else in the chapter does that job.
The greenhouse effect, measured rather than described
What you need: two identical glass jars · two thermometers · plastic film or a lid · a sunny windowsill · a stopwatch
- Put a thermometer in each jar, bulb in the middle of the air, not touching the glass
- Seal one jar with plastic film. Leave the other open
- Write down both starting temperatures
- Put both in direct sunlight, the same distance from the light, the same way round
- Read both every two minutes for twenty minutes
- Plot both sets of readings on one set of axes
| Open jar | Sealed jar | |
|---|---|---|
| After 20 minutes | Warmer than the room | Warmer still, usually by 3 to 8 °C |
| Shape of the line | Rises, then flattens | Rises faster, flattens higher |
The result is the gap between the two lines, not the final number. A learner who writes down only the last reading has no graph and no investigation.
What this experiment actually shows, and what it does not
Here is the part almost every version of this experiment leaves out.
The sealed jar gets hotter because the warm air cannot escape. Convection is blocked. That is exactly how a greenhouse works, and it is why the effect is named after one.
The real atmosphere does not work that way, because there is no lid on it.
| Your sealed jar | The atmosphere | |
|---|---|---|
| What is stopped | Warm air moving away | Infrared radiation escaping to space |
| What does the stopping | The plastic film | Carbon dioxide, methane and water vapour |
| Is there a physical barrier? | Yes | No |
Sunlight passes through the atmosphere and warms the ground. The ground radiates that energy back as infrared. Greenhouse gases absorb some of it and send part back down. Nothing is trapped in a container; the energy is delayed on its way out.
Knowing where a model stops being true is a real skill, and it is worth three marks on our worksheet.
The version that isolates the gas
If you want the experiment to test the gas rather than the lid:
- Two identical clear plastic bottles, both sealed, both under the same lamp at the same distance
- Fill one with carbon dioxide: a spoon of bicarbonate of soda and a splash of vinegar, and let the gas push the air out
- Leave the other full of ordinary air
Now the only difference is what the bottle contains. The carbon dioxide bottle warms faster. The effect is small, so run it for at least fifteen minutes and match the conditions carefully.
The ozone hole is not global warming
These are two different problems, in two different layers, caused by two different gases, and one of them is getting better.
| Ozone depletion | Greenhouse effect | |
|---|---|---|
| Where | Stratosphere, 10 to 40 km up | Troposphere, the bottom 10 km |
| Cause | CFCs breaking ozone molecules apart | Carbon dioxide and methane absorbing outgoing infrared |
| What it does | Lets more ultraviolet reach the ground. Sunburn, skin cancer, eye damage | Warms the surface. Sea level, weather, agriculture |
| Now | Recovering. CFCs were banned from 1987 | Still getting worse |
"The hole in the ozone layer is letting the heat in" is the most common wrong answer in this topic. Ozone damage lets ultraviolet in, not heat, and it happens 40 km above where the warming happens.
The ozone layer is also the environmental problem the world actually fixed. It took an international ban, and it took about thirteen years before the recovery could be measured. That is worth a minute of any Grade 9 lesson.
Temperature and altitude, and a rule worth questioning
Most textbooks say the temperature falls 1 °C for every 100 m you climb. Use it in the calculations, because that is what gets marked.
The real average is closer to 0,65 °C per 100 m.
| From 15 °C at the ground | Textbook rule | Closer to reality |
|---|---|---|
| 2 000 m | -5 °C | about 2 °C |
| 8 800 m, the summit of Everest | -73 °C | about -42 °C |
The textbook rule is the rate for a parcel of dry air being lifted. The atmosphere as a whole cools more slowly than that, and it varies with humidity, season and time of day. Say it once and the class understands why a rule can be useful and approximate at the same time.
If it does not work
| Problem | Cause | Fix |
|---|---|---|
| Both jars read the same | Unequal light, or too short a run | Twenty minutes, both in the same patch of sun |
| The open jar is hotter | It was in brighter light | Swap positions and rerun. Position beats sealing |
| Readings jump around | The bulb touches the glass, or sits in direct sun | Bulb in the middle of the air |
| The temperature stops rising | Correct. It has reached equilibrium | Say why: heat is now leaving as fast as it arrives |
| The two thermometers disagree from the start | They are not matched | Stand both in the same glass of water first and note the difference |
| Clouds | It is Term 4 | A desk lamp is more repeatable than the sun anyway |
Safety
- A sealed glass jar in the sun gets hot enough to burn. Use a cloth after twenty minutes
- Use spirit thermometers, never mercury. If your school still has mercury ones, they should be disposed of properly rather than used
- Let the fizzing finish before sealing the CO₂ bottle, or the pressure pops the lid
- Thermometers are thin glass tubes. They roll off benches
Free worksheet and marking memo
Both free, no sign up, straight to the PDF.
- Learner worksheet, 40 marks. Part A is the layers and the scale drawing, including the altitude calculations. Part B is the greenhouse investigation, with the graph and the ozone question
- Marking memorandum, including the three answers that look right and score nothing
Related practicals
- The rock cycle and the three types of rock, Grade 9. The other Term 4 topic in this strand
- Heating and cooling curve of water. The same skill: temperature against time, plotted properly
- Plant and animal cells under a microscope, Grade 9. Term 1
What you need to run it
Two jam jars and two thermometers. That is the entire apparatus list.
The jars come from a kitchen. The thermometers are the only thing worth buying properly, because the whole result is the difference between two readings, and two mismatched instruments produce a difference that is not real.
Our spirit filled thermometers are R35 for a 300 mm, -10 to 110 °C instrument, and there are 890 on the shelf. Buy four rather than two: two groups can run at once, and one always breaks.
For this particular practical the -10 to 50 °C version is the better instrument, because the divisions are finer across the range the jars actually reach. It is R54. The rest of the range is on the thermometers page.
Use spirit, not mercury. A broken spirit thermometer is a cleanup. A broken mercury thermometer is an incident report.