Chapter 18

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Across
  1. 1. NASA can communicate with astronauts above the ionosphere because the ionosphere does not reflect this
  2. 4. The rate at which solar energy enters the earth's atmosphere is called the ______________ constant.
  3. 6. In the carbon cycle, carbon is moved from the atmosphere into plants by this process
  4. 7. A region extending thousands of kilometers into space that includes the exosphere and Van Allen belts is called this
  5. 9. Most plants in the world depend on ______________ nitrogen produced by soil and marine bacteria
Down
  1. 2. Most of the direct solar energy that enters the earth is absorbed by this
  2. 3. most of the Earth's weather happens here
  3. 5. Evolutionists believe that the first life forms to appear would have been poisoned by the presence of this
  4. 8. Ozone in the atmosphere is made up of _______ oxygen atoms