The Atmosphere

1. The Atmosphere • The atmosphere is a layer of gases that surround the Earth. • These layers differ in temperature, in density, and in the relative amounts of the different gases that are present. • The two main gases in the atmosphere are nitrogen and oxygen. • Nitrogen makes up about 70% of the atmosphere, Oxygen about 20%, and the rest is a mixture of various other gases such as Carbon Dioxide, Methane, Hydrogen, Neon, etc.

2. The Atmosphere • Layers of the Atmosphere • troposphere • stratosphere • mesosphere • thermosphere

3. The Atmosphere • Troposphere:the lowest layer • Temperature drops as altitude increases • The troposphere is the densest layer • Almost all weather occurs in the troposphere.

4. The Atmosphere • stratosphere:between the troposphere and the mesosphere • temperature increases as altitude increases; • contains the ozone layer • The ozone layer shields living things on Earth’s surface from ultraviolet-radiation damage.

5. The Atmosphere • mesosphere:the coldest layer of the atmosphere, • temperature decreases as altitude increases • Temperatures in the mesosphere decrease to about -80º C.

6. The Atmosphere • thermosphere:the uppermost layer of the atmosphere • temperature increases as altitude increases • Temperatures average about 980 °C (1,796 °F) because the small amount of oxygen absorbs intense solar radiation.

7. The Atmosphere • The ionosphere: the lower thermosphere and upper mesosphere • When solar energy is absorbed, charged ions are formed. • Radio waves are reflected in the ionosphere. • Auroras take place in the ionosphere.

8. Changes in Earth’s Atmosphere • When Earth began to solidify, about 4.4 billion years ago, volcanic eruptions released a variety of gases. • The gases released by volcanoes did not include oxygen.

9. Changes in Earth’s Atmosphere • Photosynthetic bacteria contribute oxygen to the atmosphere. • Organisms evolved photosynthesis, a method of capturing energy from the sun. • Photosynthesis produces oxygen as a waste product. • Gradually the oxygen content increased to what it is today.

10. Changes in Earth’s Atmosphere • Animals produce carbon dioxide necessary for photosynthesis. • Oxygen breathing organisms evolved and released carbon dioxide as a waste product. • The oxygen-carbon dioxide cycle maintains a balance of atmospheric gases on Earth.

11. Changes in Earth’s Atmosphere • Human-made chemicals can deplete the ozone layer. • Ozone forms when the sun’s ultraviolet rays strike molecules of O2. • Ozone absorbs much of the sun’s ultraviolet radiation. • Without the ozone layer, ultraviolet radiation would damage living cells. • Chlorofluorocarbons, CFCs, are chemicals that destroy the ozone layer, but are now banned in most countries.

12. Changes in Earth’s Atmosphere • greenhouse effect:the warming of the surface and lower atmosphere of Earth that occurs when carbon dioxide, water vapor, and other gases in the air absorb and reradiate infrared radiation • Greenhouse gases trap the sun’s heat and keep Earth’s surface warm.

13. Changes in Earth’s Atmosphere • Too much carbon dioxide may cause global warming/climate change • If too much energy is absorbed by the atmosphere, global temperatures will rise. • Global warming could cause problems, such as rising ocean levels, because of melting polar icecaps, and droughts. • Combustion of coal, oil, and gas has added more carbon dioxide to the air.