earths 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, 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
• How long has the Earth been evolving?

  About 4.6 billion years
• Why is the evolution of the atmosphere considered a theory?

  It is supported by evidence but not definitive
• What was the early atmosphere mostly composed of?

  Mostly carbon dioxide
• What happened as water vapor condensed in the early atmosphere?

  It formed oceans that dissolved CO2
• What did dissolved carbon dioxide in oceans form?

  Carbon precipitates and 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 photosynthesis affect atmospheric gases?

  It decreased CO2 and increased O2 levels
• What happens to algae and plants when they die?

  They become buried and form sediments
• What do sedimentary rocks and fossil fuels trap?

  Carbon from dead organisms
• What is crude oil mainly formed from?

  Dead plankton
• What is coal made from?

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

  Calcium carbonate from marine organisms
• What are the major changes in Earth's atmosphere over billions of years?

  • First billion years: Volcanic activity produced CO2
  • Formation of oceans from condensed water vapor
  • Algae and plants evolved, reducing CO2 and increasing O2
  • Burial of organic matter formed sedimentary rocks and fossil fuels
• What is the current major composition of the 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 frame for the evolution of the atmosphere?

  Over the past 4.6 billion years
• What is the relationship between photosynthesis and the evolution of complex life?

  Increased oxygen levels allowed complex life to evolve