1. The Atmosphere Chapter 18

2. The atmosphere supports life  Living things occupy only a relative thin layer of the Earth’s crust. –The ocean and the atmosphere  The small fraction of the Earth’s environment that supports life is known as the biosphere.

3. Subdividing the Atmosphere

4. The atmosphere  The atmosphere consists of a mixture of gases extending about 100km above the earth surface.  The interactions that occur in the upper layers of the atmosphere are mostly influenced by the high-energy radiation from the sun. The chemistry of the troposphere, however, is significantly affected by human activity on earth.

5. The atmosphere and radiation  High-energy, ultraviolet radiation from the sun is damaging to living organisms.  Ozone (O 3 ) gas can absorb some radiation and can act as a protective filter.  In the stratosphere, within a band 10-30km above the earth’s surface, is the ozone layer.  This is where ozone occurs at concentrations significantly higher than in the lower regions of the atmosphere.

6. Ozone  In the ozone layer, high-energy UV radiation causes the strong double bond of diatomic oxygen molecules (O 2 ) to break to form highly reactive oxygen atoms: Some of these then combine with other oxygen molecules to form ozone. 2O22O2 O + O UV Radiation 3O33O3 2 O + O 2

7. Ozone  Ozone molecules can also absorb ultraviolet radiation, decomposing to oxygen molecules and oxygen atoms.  Overall, without human activity, the rate of formation of ozone is about the same as its rate of depletion, so the concentration of ozone in the stratosphere remains constant. 3 (g) O 3 (g) UV Radiation O 2 (g) + O(g)

8. The atmosphere and climate  The Earth has maintained its average temperature over time because of the balance between the radiation received from the sun and that reflected back into space.  Radiation of shorter wavelengths can pass through the atmosphere from the sun, such as visible light and UV.  The earth radiates back lower energy, longer wavelength radiation, such as infrared.

9.  Gases in the troposphere, such as carbon dioxide, water vapour and methane, absorb some of the reflected infrared radiation before it can reach space and radiates it back to earth as heat.  This is known as the greenhouse effect. The atmosphere and climate

11. Your Turn  Page 316  Question 1, 3 and 4

12. The atmosphere and essential gases.

13. Oxygen and Carbon Dioxide  Oxygen makes up 21% of the atmosphere and is required for respiration.  Respiration involves glucose and oxygen being broken down into carbon dioxide, water and energy.  Respiration is the major energy-producing process of most living things: C 6 H 12 O 6 (aq) + 6O 2 (g) → 6CO 2 (g) + 6H 2 O(l) + energy

14. Oxygen and Carbon Dioxide  Carbon dioxide makes up only 0.035% of the atmosphere, but provides all food sources on earth.  Photosynthesis is where plants combine carbon dioxide and water in the presence of chlorophyll and sunlight to produce glucose and oxygen. C 6 H 12 O 6 (aq) + 6O 2 (g) 6CO 2 (g) + 6H 2 O(l) Sunlight Chlorophyll

15. Carbon-Oxygen Cycle How is Carbon and Oxygen Cycled??

16. Carbon-Oxygen Cycle  Both carbon dioxide and oxygen are cycled in the processes of photosynthesis and respiration.  Carbon dioxide is also returned to the atmosphere when an organism’s wastes are decomposed.  Volcanic action and combustion of fossil fuels, add carbon dioxide to the atmosphere  The production of coal, oil and natural gas over a period of several million years. This process removes carbon from the cycle.

17. Nitrogen  Nitrogen is essential in DNA and proteins.  78% of the atmosphere is nitrogen but most living creatures cannot use it in this form.  We depend on a few species of microorganisms that can break the strong triple covalent bond within the nitrogen molecule to form simple nitrogen-containing ions such as ammonium or nitrate ions.  Plants can then use these molecules to make more complex nitrogen containing compounds which us (as animals) can then consume.

18. Nitrogen  The conversion of atmospheric nitrogen into soluble nitrogen compounds that can be used by plants is called nitrogen fixation.

19. Your Turn  Page 320  Questions 5 - 8