The atmosphere is composed of 78% nitrogen, 21% oxygen, and variable amounts of gases like carbon dioxide and water vapor. It is layered into the troposphere, stratosphere, mesosphere, and thermosphere. The troposphere extends from the surface to 12 km and temperature decreases with altitude. The stratosphere extends from 12-50 km and has increasing temperature with altitude.

1. Composition & Structure of the
Atmosphere

2. Atmosphere
• The thin layer of gas that envelopes the Earth and is held to the Earth by the force
of gravity

3. Composition of Atmosphere
• 1.Constant Gases
• 78% Nitrogen
• 21% Oxygen
• 2. Variable gases
• CO2= 0.04% of air
• Water Vapours
• Ozone

4. Layered Structure
• 4 layers
• 1.Troposphere
• 2.Stratosphere
• 3.Mesosphere
• 4.Thermosphere

5. Temperature trend

6. Troposphere
• •Bottom layer
• •Average height=12km
• •Temperature decreases with altitude
• •Lapse rate (rate of decline in
temperature)=6.5◦C/1000m
• •The upper boundary is called tropopause

7. Stratosphere
• Extends from 12km-50km
• •Exhibits positive lapse rate (called inversion)
• •It has calm, thin and clear air
• •Jets and aircrafts fly in the stratosphere
• •It contains ozone

8. Mesosphere
• Extends from 50km-80km above the Earth’s
surface
• •Temperature again increases with height
• •Here sunlight can form ionized particles and
it is called a D-layer
• •D layer is used for radio communication

9. Thermosphere
• Extended from 80km to the edge of space
• •Temperature increases very sharply
• •Ionization forms E and F layers
• •These ions can form Auroras due to their
movement

10. Aurora