What is air

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Across
  1. 2. a gas that makes up about 21 percent of Earth’s atmosphere and what humans breathe
  2. 5. the mixture of gases surrounding Earth
  3. 6. a greenhouse gas found in Earth’s atmosphere
  4. 8. a variable gas in the atmosphere; a greenhouse gas
  5. 9. a process used by plants and algae to make sugar
  6. 12. radiant energy that heats
  7. 14. it is a type of permanent gas
Down
  1. 1. a gas in the atmosphere for which the amount stays constant
  2. 3. an atmospheric gas whose amount changes based on the environment
  3. 4. a form of oxygen that forms a thin layer in the stratosphere
  4. 7. a gas that absorbs and radiates energy in the atmosphere, trapping thermal energy
  5. 8. the amount of matter in an object or sample
  6. 10. the gaseous state of water
  7. 11. the layer of gases surrounding Earth
  8. 13. a colorless, odorless gas that makes up about 78 percent of Earth’s atmosphere