Earth's atmosphere extends to about 10,000 km altitude, though 99% of its mass is in the first 30 km. It is divided into troposphere (0–12 km), stratosphere (12–50 km), mesosphere (50–85 km), thermosphere (85–600 km), and exosphere (>600 km).
Composition and function
Besides N₂ and O₂, it contains trace gases like CO₂, water vapour, ozone, and methane that regulate the greenhouse effect. The ozone layer in the stratosphere filters UV radiation. All weather phenomena occur in the troposphere, the thinnest but densest layer.