9: Chemistry of the atmosphere

• How long ago did the Earth form?

  Approximately 4.6 billion years ago
• Why are scientists uncertain about the early atmosphere's composition?

  Not enough evidence has been discovered
• What is one theory about the origin of the early atmosphere?

  It came from intense volcanic activity
• How did volcanic activity contribute to the early atmosphere?

  It released gases similar to Mars and Venus
• What gases were abundant in the early atmospheres of Mars and Venus?

  A large amount of carbon dioxide
• What other gases were present in the early atmosphere besides carbon dioxide?

  Little or no oxygen, ammonia, and methane
• What happened to the water vapor released by volcanic activity?

  It condensed to form the oceans
• What gas was probably released by volcanoes that built up in the atmosphere?

  Nitrogen
• How long have the proportions of gases in the modern atmosphere been stable?

  For approximately 200 million years
• What is the most abundant gas in the modern atmosphere?

  • Nitrogen
• What are the main components of the modern atmosphere?

  • Nitrogen
  • Oxygen
  • Argon
  • Carbon dioxide
  • Trace gases
• What process do plants use to make their own food?

  Photosynthesis
• What are the reactants in the photosynthesis equation?

  Carbon dioxide and water
• What is produced as a by-product of photosynthesis?

  Oxygen
• Write the balanced chemical equation for photosynthesis.

  6CO2(g) + 6H2O(l) → C6H12O6(aq) + 6O2(g)
• Approximately how long ago did algae first evolve?

  2.7 billion years ago
• What role did photosynthesis by primitive plants and algae play in the atmosphere?

  It released oxygen into the atmosphere
• How did the increase of oxygen in the atmosphere affect animal evolution?

  It enabled animals to evolve
• What is the equation for photosynthesis?

  • Reactants: Carbon dioxide and water
  • Products: Glucose and oxygen
  • Balanced equation: 6CO2(g) + 6H2O(l) → C6H12O6(aq) + 6O2(g)
• What is the significance of algae in the history of oxygen on Earth?

  • Algae evolved approximately 2.7 billion years ago
  • They began releasing oxygen into the atmosphere
  • This oxygen accumulation allowed for animal evolution
• What is carbon dioxide's state in water?

  It is a very soluble gas.
• How does carbon dioxide decrease in the atmosphere?

  It dissolves in water to form carbonate compounds.
• What type of rocks are formed from carbonate compounds?

  Sedimentary rocks, such as limestone.
• What role do photosynthetic organisms play in carbon dioxide levels?

  They absorb carbon dioxide from the oceans.
• What are fossil fuels formed from?

  Organisms like algae and plants.
• How is coal formed from trees?

  Wood is buried to prevent oxidation.
• What process transforms wood into coal over millions of years?

  Compression and heating.
• What are the origins of crude oil and natural gas?

  From simple plants and tiny animals.
• What happens to small organisms after they die in water bodies?

  Their remains sink and get buried under sediments.
• Why does the lack of oxygen matter in the formation of fossil fuels?

  It prevents oxidation from occurring.
• How do heat and pressure contribute to fossil fuel formation?

  They transform remains into crude oil and natural gas.
• Where is natural gas typically found in relation to crude oil?

  On top of crude oil, under sedimentary rock.
• What are two reasons for the decrease of carbon dioxide in the atmosphere over time?

  • Carbon dioxide dissolves in water forming carbonate compounds.
  • Photosynthetic organisms absorb carbon dioxide from oceans.
• Why is the mean temperature of -18°C significant for life on Earth?

  It is too cold to support life as we know it
• What are three greenhouse gases present in the atmosphere?

  • Water vapour
  • Carbon dioxide
  • Methane
• How do greenhouse gases affect heat radiated from the Earth?

  They absorb heat and release energy in all directions
• What is the process called that describes how greenhouse gases keep the Earth warm?

  The greenhouse effect
• What happens to electromagnetic radiation at most wavelengths when it reaches the Earth's atmosphere?

  It passes through the atmosphere
• What does the Earth do after absorbing most of the radiation?

  It warms up
• How does the Earth radiate energy after warming up?

  As infrared radiation