Geography Topic
The atmosphere
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Study focus - 3 things
- The atmosphere is the layer of gases around Earth, held in place by gravity
- 5 layers from the ground up: Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere
- Composition is mostly nitrogen (78%) and oxygen (21%) — not the other way around
Section 1What the atmosphere is
The atmosphere is the layer of gases surrounding Earth, held in place by gravity. Without it, there would be no breathable air, no protection from radiation or meteors, and no liquid water — life as we know it couldn't exist.
Section 2The 5 layers (from the ground up)
Troposphere — ground level to about 12 km, where ALL weather happens. Stratosphere — 12 to 50 km, contains the ozone layer. Mesosphere — 50 to 85 km, where meteors burn up. Thermosphere — 85 to 600 km, very hot, contains the aurora (Northern and Southern Lights). Exosphere — above 600 km, fades into outer space.
Section 3What it is made of
About 78% nitrogen, 21% oxygen, with the remaining 1% made up of argon, carbon dioxide, water vapour, and trace gases. The exact mix changes slightly with altitude and weather, but the nitrogen-oxygen dominance is constant.
Section 4Why it matters
Four big jobs: provides the air we breathe; blocks harmful UV radiation (via the ozone layer); burns up most meteors before they reach the surface; traps heat through the greenhouse effect, keeping Earth's temperature in the range that supports life.
Examples
If you climb a tall mountain, which layer of the atmosphere are you still in?
The troposphere. Even the tallest mountain (Everest, ~9 km) doesn't reach the top of the troposphere (~12 km). All weather and almost all human activity happens in this lowest layer.
Why do we get sunburnt less than we would without the atmosphere?
The ozone layer in the stratosphere absorbs most of the Sun's UV radiation before it reaches the ground. Without ozone, sunburn would be far more severe and skin cancer rates would skyrocket.
Now let's water it
Session runs notes to flashcards to quiz back-to-back.