2. I. Earth’s Past Atmospheres: 1.) Volcanoes and lava covered earth which gave off NH 3, CH 4, which enters earth’s first atmosphere. 3.) The suns rays broke down the first atmosphere into more simple substances over a long time. 4.) Earth cools down and stops giving off as much NH 3, and CH 4. A. Changing of earth’s first atmosphere: 2.) Earth’s surface was bombarded with Comets and meteoroids, bringing H 2 0 to our planet. This water then evaporated and entered earth’s atmosphere. 1.) Earth’s current atmosphere was very different compared to what it had in the past. 2.) Many events had to take place to get an atmosphere like we have today.

3. B. Changing of earth’s second atmosphere: 1. The second atmosphere has N 2, H 2, CO 2, & H 2 0. 2. H 2 gets pushed to the outer parts of our solar system by the solar wind after it escapes earth’s gravitational pull. 3. Earth cools to the point that most of the H 2 0 can turn into liquid. This liquid begins to cover the earth’s surface. 4. This allows for the beginnings of life. Bacteria use CO 2 and sun light to make food. As a waste product O 2 is given off and enters the atmosphere. 5. After millions of years our current atmosphere of N 2, O 2, CO 2 & H 2 O forms.

4. II. Earth’s Present Atmosphere: A. Divisions of Earth: 1. Lithosphere -Solid portion of the earth. 2. Hydrosphere -Water portion of the earth. 3. Atmosphere -Gas portion of the earth. B. Composition of the Earth’s Atmosphere: 1. 78 % Nitrogen 2. 21 % Oxygen 3. 1 % - 4 % Trace Elements

5. 4.) Trace Elements- the smallest portion of our atmosphere 1-4 %. Many Gases. 5.) Examples of trace elements are: H 2 O (Solid, Liquid or Gas), CO 2, He, O 3, Methane, Dust and Salt etc.. B. Composition of the Earth’s Atmosphere Cont.:

6. III Structure of the Earth’s Atmosphere: A. Troposphere: 1.) Layer closest to the ground. 2.) Nicknamed the “Weather Sphere”. 3.) Most dense layer of the atmosphere. ( 75 % of the atmosphere) 4.) As you get higher in this layer temperature decreases. 1.) Made up of five layers. 2.) Temperature & Air Pressure changes help scientists distinguish the difference between each layer.

7. B. Stratosphere: 1.) 2nd layer of earth’s atmosphere. 2.) The ozone layer is part of this layer. 3.) Temperature increases, as you get higher due to the ozone absorbing UV Radiation. 4.) The highest large passenger air crafts will fly.

8. C. Mesosphere: 1.) 3rd layer of the atmosphere. 2.) Most meteors burn up by the time they leave this layer. 3.) As you get higher in this layer temperature decreases.

9. D. Thermosphere: 1.) 4th layer of the atmosphere. 2.) T.V. & Radio satellites revolve around earth in this layer. 3.) The Ionosphere is a very important part of the Thermosphere. a.) Ionosphere- area inside the thermosphere where, from the suns rays, change gases into ions. b.) Radio waves bounce off of these ions. c.) Aurora Borealis occur there when energy strike these ions, which creates awesome light shows

10. E. Exosphere: 1.) Outer most layer of the earth’s atmosphere. 2.) The space shuttle orbits earth in this layer on most space missions. 3.) No clear boundary between this layer and space. 4.) Sometimes considered part of the thermosphere.

11. IV. Earth’s Ozone Layer: 1. Ozone is a form of oxygen. 2. One atom of oxygen is O, one molecule of breathing oxygen is O 2, and one molecule of ozone is O 3. B. Effects of Ozone: 1. Ozone absorbs most of the ultra violet radiation that enters the earth. 2. Too much exposure to UV radiation can damage most living things. 3. In mammals it WILL! cause CANCER! A. Ozone: 4. About 800,000 to 1,000,000 Americans develop skin cancer every year. 5. About 10,000 Americans die every year from skin cancer.

12. C. Thinning of the Ozone Layer: 1. The ozone layer is thinning and in some areas does not even exist. 2. The biggest hole is over Antarctica. 3. Chlorofluorocarbons or CFC’s are being blamed for thinning most of the ozone layer. 4. CFC’s are made up of 3 Chlorine atoms, 1 Fluorine atom, and 1 Carbon atom. 5. CFC’s are found in refrigerating systems, aerosol cans, and Styrofoam packaging.

13. D. Effect of CFC’s: 1. One chlorine atom, from a CFC molecule, reacts with one of the oxygen atoms, from an ozone molecule. 2. That splits up the ozone molecule into a chlorine oxygen compound and a breathing oxygen molecule. 3. A free oxygen atom can break the bonds of the chlorine oxygen compound. This forms a single chlorine atom and a breathing oxygen molecule. 4. The chlorine atom then will attack another ozone molecule, which will start the process all over again.