1.4.3 Atmospheric Evolution

• What were the primary gases released from volcanic eruptions in the early Earth's atmosphere?

  Water vapor, carbon dioxide
• What were the key characteristics of the early Earth's atmosphere?

  High greenhouse gases
• What does the ozone layer protect Earth from?

  Harmful UV radiation
• What is the chemical equation for photosynthesis?

  $CO₂ +$$H₂O → C₆H₁₂O₆ +$$O₂$
• In the early atmosphere, nitrogen (N₂) made up 5%
• Photosynthesis reduced the levels of carbon dioxide and increased the levels of oxygen
• What percentage of carbon dioxide (CO₂) is in the present atmosphere?

  0.04%
• How is ozone (O₃) formed in the upper atmosphere?

  Oxygen reacts with sunlight
• Nitrogen (N₂) in the early atmosphere made up 5%.
• Nitrogen (N₂) in the early atmosphere made up 5%.
• What greenhouse gas made up 15% of the early atmosphere?

  Carbon dioxide
• Nitrogen (N₂) in the present atmosphere makes up 78%.
• The early Earth's atmosphere lacked free oxygen
• What percentage of the early Earth's atmosphere was methane?

  3%
• What does the ozone layer protect the Earth from?

  UV radiation
• What is the approximate percentage of nitrogen in the present atmosphere?

  78%
• Arrange the following processes in the order they occurred in the early Earth's atmospheric transformation:

  1️⃣ Early algae and plants absorb CO₂ and H₂O

  2️⃣ Photosynthesis produces glucose and oxygen

  3️⃣ Oxygen reacts with iron in the oceans

  4️⃣ Oxygen accumulates in the atmosphere

  5️⃣ Ozone layer forms
• What two substances did early algae and plants absorb from the atmosphere during photosynthesis?

  CO2 and H2O
• What layer formed due to the build-up of oxygen in the atmosphere?

  Ozone layer
• What percentage of nitrogen was present in the early Earth's atmosphere?

  5%
• The early Earth's atmosphere contained free oxygen.

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


  True
• Match the atmospheric component with its percentage in the early Earth and present atmospheres:

  Nitrogen ↔️ 5% in early, 78% in present

  Oxygen ↔️ 0% in early, 21% in present

  Carbon Dioxide ↔️ 15% in early, 0.04% in present

  Water Vapor ↔️ 80% in early, 1-4% in present
• How did the reduction of carbon dioxide in the early atmosphere affect Earth's climate?

  It cooled the planet
• Steps in the transformation of Earth's early atmosphere

  1️⃣ Photosynthesis by early algae and plants

  2️⃣ Oxygen build-up in the oceans

  3️⃣ Formation of the ozone layer
• Oxygen (O₂) in the present atmosphere makes up 21%
• Match the key process with its effect on the atmosphere:

  Photosynthesis ↔️ Reduces CO₂, increases O₂

  Oxygen build-up ↔️ Forms the ozone layer
• Water vapor (H₂O) in the present atmosphere varies between 1-4%.
• What gas reacted with sunlight to form the ozone layer?

  Oxygen
• Water vapor in the early atmosphere made up 80%.
• What was the initial driver of the early Earth's atmosphere?

  Volcanic activity
• The early Earth's atmosphere was 80% water vapor.

  True
• Oxygen in the early Earth's atmosphere initially reacted with iron in the oceans.

  True
• Match the atmospheric component with its approximate percentage in the early Earth's atmosphere:

  Water Vapor (H₂O) ↔️ 80%

  Carbon Dioxide (CO₂) ↔️ 15%

  Methane (CH₄) ↔️ 3%

  Ammonia (NH₃) ↔️ 2%
• The concentration of water vapor in the present atmosphere varies between 1% and 4%
• The oxygen build-up in the atmosphere eventually led to the formation of the ozone layer
• Photosynthesis reduced the levels of carbon dioxide and increased oxygen in the early atmosphere.


  True
• The ozone layer allowed for the evolution of more complex life forms on Earth.


  True
• Steps in the transformation of the early Earth's atmosphere:

  1️⃣ Early algae and plants absorb CO2 and H2O

  2️⃣ Photosynthesis converts CO2 and H2O into glucose and O2

  3️⃣ Oxygen levels increase in the atmosphere

  4️⃣ The ozone layer forms

  5️⃣ Life evolves due to UV protection
• What percentage of oxygen is present in the modern Earth's atmosphere?

  21%