1. ATMOSPHERE
Science

2. Earth’s Atmosphere
Atmosphere – the blanket of air that surrounds Earth.
Earth’s atmosphere is made up of nitrogen, oxygen, carbon dioxide, water vapor, and many other gases, as well as particles of liquids and solids.

3. Layers of the Atmosphere
The atmosphere is divided into four main layers:
the troposphere
the stratosphere
the mesosphere
the thermosphere. The thermosphere is further divided into the ionosphere and the exosphere.

4. Air Pressure
The pressure caused by the weight of a column of air pushing down on an area.
A barometer measures air pressure.

5. Measuring Air Pressure
Air pressure pushes down on the surface of the mercury in the dish, causing the mercury in the tube to rise. The air pressure is greater on the barometer on the right, so the mercury is higher in the tube.

6. Measuring Air Pressure
This diagram shows an aneroid barometer. Changes in air pressure cause the walls of the airtight metal chamber to flex in and out. The needle on the dial indicates the air pressure.

7. Air Pressure and Altitude
Air pressure decreases as altitude increases.

8. Altitude and Density
The density of air decreases as altitude increases. Air at sea level has more gas molecules in each cubic meter than air at the top of a mountain.

9. Effects of Pollution
Air pollution can cause many different problems. This table shows the health effects of air pollution. Pollen also can cause difficulties for people with allergies.

10. How Heat Is Transferred
Heat is transferred in three ways: radiation, conduction, and convection.

11. Heat Transfer radiation – the transfer of energy by waves
conduction – the transfer of thermal energy through matter by actual contact of molecules
Convection – the transfer of thermal energy due to density differences.

12. Temperature and the Movement of Molecules
The iced tea is cold, so its molecules move slowly. The herbal tea is hot, so its molecules move faster than the molecules in the iced tea.

13. Energy From the Sun
Most of the energy from the sun travels to Earth in the form of visible light and infrared radiation. A small amount arrives as ultraviolet radiation.

14. Energy in the Atmosphere
Some sunlight is absorbed or reflected by the atmosphere. The rest passes through to the surface.

15. Greenhouse Effect
When Earth’s surface is heated, it radiates most of the energy back into the atmosphere as infrared radiation. Much of this energy is held by the atmosphere, warming it.