1. ATMOSHERE The earth's atmosphere is a very thin layer wrapped around a very large planet. Two gases make up the bulk of the earth's atmosphere: nitrogen, which comprises 78% of the atmosphere, and oxygen, which accounts for 21%. Various trace gases make up the remainder. Based on temperature, the atmosphere is divided into four layers: the troposphere, stratosphere, mesosphere, and thermosphere.

2. COMPOSITION OF AIR

5. TROPOSPHERE (0 – 12 km) Tropo is a Greek word means turn or change It begins at the surface and extends to between 7 km (23,000 ft) at the poles and 17 km (56,000 ft) at the equator Contains 75% of the gases in the atmosphere. The temperature drops about 6.5 degrees Celsius for every kilometer above the earth's surface.

6. Normal weather and clouds occur Heating of the Surface creates warm air at surface Warm air rises, but air expands as it rises and cools as it expands (Adiabatic cooling) Heating + Adiabatic Cooling = Warm air at surface, cooler air above Tropopause - located at the top of the troposhere. The temperature remains fairly constant here. This layer separates the troposphere from the stratosphere

8. STRATOSPHERE (12 – 50 km) Latin word "stratus" meaning spreading out. The temperature remains fairly constant (-60 degrees Celsius). This layer contains the ozone layer. Ozone(O 3 ) acts as a shield for in the earth's surface. It absorbs ultraviolet radiation from the sun. This causes a temperature increase in the upper part of the layer.

9. About 90% of the ozone in our atmosphere is contained in the stratosphere. It is mainly located in the lower portion of the stratosphere from approximately 15–35 km The boundary between the mesosphere and the stratosphere, typically 50 to 55 km is named as stratopause.

10. MESOPHERE (50 – 80 km) Greek word “meso" meaning middle. The temperature drops in this layer to about - 100 degrees Celsius. This is the coldest region of the atmosphere. This layer protects the earth from meteoroids. They burn up in this area. The boundary between the thermosphere and the mesosphere is named as mesopause.

11. THERMOSPHERE (above 80 km) Contains two regions namely, Ionosphere Exoshere Thermosphere means "heat sphere". The temperature is very high in this layer because ultraviolet radiation is turned into heat. Temperatures often reach 2000 degrees Celsius or more.

12. IONOSPHERE (80 – 550 KM) Gas particles absorb ultraviolet and X-ray radiation from the sun. The particles of gas become electrically charged (ions). Radio waves are bounced off the ions and reflect waves back to earth. This generally helps radio communication.

13. EXOSPHERE (550 – 1000 km) Contain free-moving particles Air is very thin here. This is the area where satellites orbit the earth.

14. MAGNETOSPHERE (above 1000 km) The area around the earth that extends beyond the atmosphere. The earth's magnetic field operates here. It begins at about 1000 km. It is made up of positively charged protons and negatively charged electrons. This traps the particles that are given off by the sun.