Evolution of the Atmosphere

• What is the composition of the Earth's atmosphere?

  About 80% nitrogen and 20% oxygen
• What gases make up less than one percent of the Earth's atmosphere?

  Carbon dioxide, water vapor, and noble gases
• What role did volcanic activity play in the early atmosphere?

  It created a carbon dioxide-rich atmosphere
• How did algae and plants affect atmospheric composition?

  They reduced CO2 and increased oxygen levels
• What is the current theory about the evolution of the atmosphere based on?

  Evidence from the past 4.6 billion years
• What was the state of the Earth during the first billion years?

  The Earth was dry with intense volcanic activity
• What gases were produced by volcanic activity in the early atmosphere?

  Carbon dioxide, water vapor, and nitrogen
• What happened to carbon dioxide as water vapor condensed?

  It dissolved in the oceans and formed sediments
• When did algae begin to appear in Earth's history?

  About 2.7 billion years ago
• What process do algae and green plants use to produce oxygen?

  Photosynthesis
• How did the evolution of algae and plants impact life on Earth?

  Allowed more complex life like animals to evolve
• What happens to algae and green plants when they die?

  They become buried and form sedimentary rock
• What types of fossil fuels are formed from dead plankton?

  Crude oil and natural gas
• What is coal primarily made from?

  Thick deposits of dead plant material
• What is limestone mostly composed of?

  Calcium carbonate from marine organisms
• What are the key stages in the evolution of the Earth's atmosphere?

  • Intense volcanic activity produced CO2 and other gases
  • Water vapor condensed to form oceans
  • Algae and plants evolved, reducing CO2 and increasing oxygen
  • Sedimentary rocks and fossil fuels formed from dead organisms
• What is the current composition of the Earth's atmosphere?

  Mostly oxygen and nitrogen
• What is the significance of sedimentary rock and fossil fuels in relation to the atmosphere?

  They trap carbon and prevent it from re-entering
• What is the time span of Earth's history mentioned in the material?

  4.6 billion years
• Why is the theory of atmospheric evolution still considered a theory?

  Because it is based on evidence, not certainty