Gases of the Atmosphere

• State the proportions of the gases in Earth's atmosphere.

  Approximately 80% Nitrogen N2, 20% Oxygen O2 and small amounts of carbon dioxide CO2, water vapour H2O and Nobel gases.
• Why is the evidence for the Earth's early atmosphere limited?

  Because of the timescale of 4.6 billion years.
• How were gases and water vapour formed during the first 1 billion years of Earth's existence?

  Intense volcanic activity
• Name the gases formed during the first billion years of Earth's existence.

  Carbon dioxide, water vapour, methane (CH4), ammonia (NH3) and nitrogen (N2).
• How were oceans formed from the water vapour in the early atmosphere?

  Water vapour condensed as Earth cooled.
• Name two planets that have atmospheric compositions today that are similar to that of the Earth's during the 1 billion years of Earth's existence.

  Mars and Venus.
• Why did Nitrogen build up in our atmosphere?

  Because it is inert.
• After the first 1 billion years of Earth's existence the proportion of CO2 began declining, explain why.

  CO2 dissolved in the oceans where it reacts and forms carbonate precipitates. The precipitates formed sediment. Most of the CO2 is still locked up in these sediments as rock
• About 2.7 billion years ago the amount of CO2 decreased at the same rate that O2 increased, explain why.

  Algae and plants carried out photosynthesis turning CO2 into O2.
• Give the word equation for photosynthesis.

  Carbon dioxide + water --> oxygen + glucose
• Write a balanced symbol equation for photosynthesis.

  6CO2 + 6H2O --> C6H12O6 + 6O2
• When did animals evolve?

  Long after algae and plants, when the O2 levels were high enough for them to exist.
• State the 3 ways in which CO2 levels decreased in our atmosphere and list them in order of when they happened.

  1. Dissolved in oceans to form carbonate precipitates.

  2. Photosynthesis.

  3. Formed fossil fuels
• Explain how CO2 became locked up in limestone.

  CO2 dissolved in the oceans where it reacts and forms carbonate precipitates. The precipitates formed sediment. Over millions of years layers of sediment were compacted under high pressure to form rock.
• Explain how CO2 became locked up in coal.

  Plants turn CO2 into glucose in photosynthesis. They get buried in sediment and after millions of years of high heat and pressure turn into coal.
• Explain how CO2 became locked up in natural gas and oil.

  Plants turn CO2 into glucose in photosynthesis. They get consumed by animals. The animals get buried under sediment and after millions of years of high temperature and pressure turn into natural gas and oil.
• Why is it important for our atmosphere to contain greenhouse gases?

  To maintain temperatures high enough to support life.
• Name 3 greenhouse gases.

  Water vapour, carbon dioxide and methane.
• Explain the greenhouse effect.

  Greenhouse gases allow short wavelength infrared radiation to pass through the atmosphere to the Earth’s surface but absorb the outgoing long wavelength radiation from the Earth's surface causing an increase in temperature.
• What human activity could be contributing to increased CO2 in the atmosphere?

  Combustion of fossil fuels and deforestation.
• What human activities could be contributing to increased CH4 in the atmosphere?

  More cattle farming and decomposition of waste in landfill sites.
• Why is there doubt about human driven climate change in the scientific community?

  Because global climate change is a complex system that cannot be easily modelled.
• What problems are caused by the difficulties in modelling climate change?

  It leads to simplified models, speculation, opinions in media that are based on only parts of the evidence and may be biased.
• What presently is the major cause of climate change on Earth?

  Increased average global temperatures.
• What is carbon footprint?

  Total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event.
• How can carbon footprint be reduced? Reducing emissions of carbon dioxide and methane.
• What actions can be taken to reduce carbon footprint?

  Increased use of renewable energy supplies, energy conservation, carbon capture and storage, carbon taxes, carbon off-setting.
• Why is it difficult to reduce global carbon footprint?

  Scientific disagreement over causes and consequences of global climate change, lack of public information and education, lack of lifestyle changes, poor economies in some countries, incomplete international co-operation.
• What is the name of the reaction in which carbon dioxide is formed from fossil fuels?

  Combustion.
• State the gases formed from our use of fossil fuels?

  Carbon dioxide, water vapour, carbon monoxide, sulfur dioxide, oxides of nitrogen
• Why is sulfur dioxide formed if fossil fuels are hydrocarbons?

  Fossil fuels often contain sulfur impurities
• What is meant by the word impurity?

  A substance that's mixed with another that prevents it being pure.
• Which gases are pollutants formed from using fossil fuels?

  Unburned hydrocarbons, carbon dioxide, carbon monoxide, sulfur dioxide, oxides of nitrogen.
• Give the molecular formulae of carbon monoxide.

  CO.
• Give the molecular formulae of sulfur dioxide.

  SO2.
• What are oxides of nitrogen?

  Nitrogen chemically bonded to oxygen. There are several types e.g. NO, NO2, N2O4
• Name a solid pollutant that comes from using fossil fuels.

  Carbon particulates (soot).
• Describe how carbon monoxide and carbon particulates are formed.

  During incomplete combustion of fossil fuels.
• What causes incomplete combustion?

  When there is insufficient oxygen for complete combustion.
• Describe how sulfur dioxide is formed as a pollutant.

  Sulfur in fossil fuels reacts with oxygen from the air at high temperatures to form sulfur dioxide.