9.1 The composition and evolution of the Earth's atmosphere

• Over billions of years, the Earth's atmosphere evolved due to processes like volcanic activity, photosynthesis, and the formation of the ozone layer
• What is the current percentage of oxygen in the Earth's atmosphere?

  21%
• Match the gas with its initial and current composition in the atmosphere:

  Nitrogen ↔️ 80% initially, 78% currently

  Carbon dioxide ↔️ 20% initially, 0.04% currently

  Oxygen ↔️ Trace amounts initially, 21% currently
• Which gas released by volcanic activity contributes to the greenhouse effect?

  Carbon dioxide
• Order the following processes involved in the introduction of oxygen into the Earth's atmosphere:

  1️⃣ Evolution of cyanobacteria

  2️⃣ Photosynthesis

  3️⃣ Great Oxidation Event
• In photosynthesis, cyanobacteria convert carbon dioxide and water into oxygen and glucose
• Sequence the key processes involved in oxygen production and accumulation.

  1️⃣ Photosynthesis by cyanobacteria

  2️⃣ Conversion of CO₂ and H₂O into O₂ and glucose

  3️⃣ Great Oxidation Event
• Over billions of years, the Earth's atmosphere evolved due to processes like volcanic activity and the formation of the ozone layer.
• Match the gas with its effect on the atmosphere:

  Carbon dioxide ↔️ Greenhouse effect

  Sulfur dioxide ↔️ Reflects sunlight

  Water vapor ↔️ Cloud formation
• Arrange the gases from their highest to lowest current atmospheric composition percentage.

  1️⃣ Nitrogen (N₂)

  2️⃣ Oxygen (O₂)

  3️⃣ Carbon dioxide (CO₂)
• Volcanic activity initially created a CO₂-rich atmosphere, but the cooling effect of sulfur dioxide helped balance greenhouse warming.
• What was the primary composition of the Earth's initial atmosphere?

  Nitrogen and carbon dioxide
• Photosynthesis reduced carbon dioxide levels and increased oxygen levels in the atmosphere.

  True
• As photosynthetic organisms evolved, they absorbed vast amounts of carbon dioxide and released oxygen
• Volcanic activity releases gases that have both warming and cooling effects on the atmosphere.


  True
• Oxygen production began with the evolution of cyanobacteria
• What type of organisms initiated oxygen production on Earth?

  Cyanobacteria
• The Great Oxidation Event occurred due to the accumulation of oxygen in the atmosphere.


  True
• What was the dominant gas in the Earth's initial atmosphere?

  Nitrogen
• The current oxygen level in the Earth's atmosphere is approximately 21%.


  True
• What is the primary cooling effect of sulfur dioxide in the atmosphere?

  Reflects sunlight
• The Great Oxidation Event led to a significant decrease in carbon dioxide levels in the Earth's atmosphere.


  True