The document describes the composition and layers of Earth's atmosphere. It explains that the atmosphere contains nitrogen, oxygen, and carbon dioxide. It also discusses the mechanisms of heat transfer in the atmosphere, including radiation, conduction, and convection. Finally, it explains the greenhouse effect, how greenhouse gases like carbon dioxide and methane trap heat in the atmosphere and warm the planet.

1. Chapter 3, Section 2

2. Learning Objectives Describe the composition and layers of the Earth’s atmosphere. Explain three mechanisms of heat transfer in Earth’s atmosphere. Explain the greenhouse effect.

3. The Atmosphere Atmosphere – the mixture of gases that surrounds the Earth Contains mostly nitrogen, oxygen, carbon dioxide These gases are constantly added and removed Animals and humans breath in and out Plants produce food Volcanoes erupt Cars

5. Composition of the Atmosphere Nitrogen = 78% Volcano eruptions Dead plants and animals decay Oxygen = 21% Plants Other Gases = 1% Argon Carbon Dioxide Methane Water Vapor

6. Composition of the Atmosphere Atmosphere also contains atmospheric dust Mainly soil Salt Ash from fires Volcanic ash Particulate matter from combustion Skin Hair Bits of clothing Pollen Bacteria and viruses aerosols

7. Air Pressure Earth’s atmosphere is pulled toward Earth’s surface by gravity This makes the atmosphere denser near Earth’s surface Almost the entire mass of Earth’s atmospheric gases is located with 30 km of the surface. The air is less dense at higher altitudes. This makes breathing more difficult.

9. Layers of the Atmosphere The atmosphere is divided into four layers based on temperature changes that occur at different distances above the Earth’s surface. Troposphere Stratosphere Mesosphere Thermosphere

11. The Troposphere Closest to Earth’s surface 18 km above Earth’s surface Almost all weather occurs here Densest atmospheric layer Temperature decreases as altitude increases

12. The Stratosphere From 18 km to about 50 km Temperature rises as altitude increases in stratosphere Ozone in the stratosphere absorbs the sun’s ultraviolet (UV) energy and warms the air Ozone, O 3 , is made up of three oxygen atoms Almost all ozone in the atmosphere is located in the ozone layer of the stratosphere Ozone reduces the amount of UV radiation that reaches Earth.

13. The Mesosphere From 50 km to 80 km above Earth’s surface The coldest layer of the atmosphere Temperatures as low as -93°C.

14. The Thermosphere The layer farthest from the Earth’s surface Nitrogen and oxygen absorb solar radiation The absorption causes atoms to be electrically charged. These ions radiate energy as light. Temperatures above 2,000°C If we could travel here, it would not feel hot to us Air particles that strike one another transfer heat The air in the thermosphere is so thin that air particles rarely collide so they rarely transfer heat.

19. Three Types of Heat Transfer Radiation – Transfer of energy across space Conduction – Flow of heat from a warmer object to a colder object when placed in direct contact Convection – The transfer of heat by air currents

20. Conduction, Convection, Radiation

21. Heating of the Atmosphere Solar energy reaches Earth as electromagnetic radiation. Electromagnetic radiation includes visible light, infrared radiation, and ultraviolet light. Almost half of the solar energy that enters the atmosphere passes through and reaches Earth’s surface The rest is absorbed in the atmosphere by clouds, gases and dust or it is reflected by the Earth’s surface.

22. Movement of Energy in the Atmosphere Weather is caused by air that is constantly moving upward, downward or sideways Currents of less dense air, warmed by the Earth’s surface, rise into the atmosphere. Currents of denser, cold air sink toward the ground. As currents of air rise into the atmosphere they cool off Eventually, the air current becomes more dense than the air around it and sinks. Convection current – Continual process of warm air rising and cool air sinking. A circular motion.

25. The Greenhouse Effect A greenhouse is a building where plants are grown. Solar radiation enters the building and heats up the inside faster than heat can escape.

26. Greenhouse Gases Greenhouse Gases – The gases in our atmosphere that trap and radiate heat None of the greenhouse gases have a high concentration in the Earth’s atmosphere The most abundant greenhouse gases are Water vapor (varies because of natural processes) Carbon dioxide (varies because of industry) Methane (varies because of industry) Nitrous oxide

27. The Greenhouse Effect The gases in Earth’s atmosphere act like the glass in a greenhouse. Sunlight penetrates the Earth’s atmosphere and heats the surface of the Earth. The Earth’s surface radiates heat back to the atmosphere where only some of the heat escapes into space. The rest of the heat is absorbed by the greenhouse gases, which warms the air. Heat is then radiated back toward the surface of the Earth. Without the greenhouse effect Earth would be too cold to live.