C13 - The Earth's atmosphere

• How long ago do scientists think the Earth was formed?

  About 4.6 billion years ago
• What was the Earth like during its first billion years?

  It was a hot, turbulent place
• What covered the Earth's surface during its early years?

  Volcanoes belching fire and gases
• What evidence do scientists use to reconstruct the early atmosphere?

  Gas bubbles trapped in ancient rocks
• What gases are suggested to have formed the early atmosphere?

  Carbon dioxide, water vapour, nitrogen
• How did water form the first oceans on Earth?

  Water vapour condensed and fell as rain
• What is one theory about the source of water on Earth?

  Comets brought water to Earth
• What was the composition of the atmosphere as Earth stabilized?

  Mainly carbon dioxide with some water vapour
• Which planets have atmospheres similar to early Earth?

  Mars and Venus
• What happened to the atmosphere after life first appeared on Earth?

  The atmosphere remained stable
• When do scientists believe life began on Earth?

  About 3.4 billion years ago
• How did algae contribute to the atmosphere's oxygen levels?

  They produced oxygen through photosynthesis
• What was the significance of increasing oxygen levels in Earth's atmosphere?

  Allowed for the evolution of animal life
• What is the chemical equation for photosynthesis?

  6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
• How did carbon dioxide levels decrease in the atmosphere?

  Through photosynthesis by plants and algae
• What percentage of today's atmosphere is nitrogen?

  About 80%
• What percentage of today's atmosphere is oxygen?

  About 20%
• What happens to carbon dioxide in the oceans?

  It dissolves and forms carbonate compounds
• How did fossil fuels form from ancient organisms?

  From remains buried under sediment over time
• What is the chemical formula for calcium carbonate?

  CaCO₃
• What gases did volcanoes produce in the early atmosphere?

  Nitrogen, methane, and ammonia
• Why did nitrogen levels remain high in the atmosphere?

  Nitrogen is a very unreactive gas
• What are the main greenhouse gases in the Earth's atmosphere?

  Carbon dioxide, methane, and water vapour
• How do greenhouse gases warm the Earth?

  They absorb infrared radiation from the surface
• What has caused the increase in carbon dioxide levels recently?

  Burning fossil fuels for energy
• What happens to carbon when fossil fuels are burned?

  It is released as carbon dioxide
• What is the chemical equation for the combustion of propane?

  C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
• How does deforestation affect carbon dioxide levels?

  It reduces carbon dioxide absorption by trees
• What evidence do scientists use to study past atmospheric conditions?

  Ice cores drilled from Greenland's ice sheet
• What do ice cores reveal about atmospheric gases?

  Composition of gases over time
• How long ago were carbon dioxide levels higher than today?

  Over the last 440,000 years
• What happens to carbon dioxide solubility as temperature rises?

  It becomes less soluble in water.
• Why are oceans less effective as CO₂ sinks when temperature rises?

  Higher temperatures reduce CO₂ solubility.
• What do most scientists agree has started?

  A trend in global warming.
• What is the basis for scientists' views on global warming?

  Evidence presented in scientific journals.
• What do some scientists argue about observed temperature rises?

  They are due to natural variations.
• What is one source of evidence for climate change?

  Ice cores from Greenland's ice sheet.
• How do scientists analyze trapped air in ice cores?

  To find changes in gas composition over time.
• How long have current levels of carbon dioxide been higher?

  Higher than any time in the last 440,000 years.
• What does Figure 3 show regarding temperature and CO₂ concentration?

  Changes over the past 150,000 years.