earth's atmosphere

• earth was formed approximately 4.6 billion years ago

  thats ages ago (no shit), so scientists make educated guesses about the composition of the earth's atmosphere. there is not enough evidence
• where the atmosphere came from

  one theory is that the early atmosphere came from intense volcanic activity, which released gases making the atmosphere very similar to present day venus or mars

  • large amount of carbon dioxide
  • little or no oxygen
  • small amounts of other gases (ammonia, methane)
• volcanic activity also released water vapour, which condensed to form the oceans as the earth cooled.

  nitrogen was probably also released, and was able to build up because it is unreactive
• modern day atmosphere

  for the last approximately 200million years, earth's atmosphere has remained relatively stable

  A) nitrogen

  B) oxygen

  C) water

  
• how oxygen increased

  plants make their own food by photosynthesis

  6CO2(g) + 6H2O(l) → C6H12O6(aq) + 6O2(g)

  carbon dioxide + water ---> glucose + oxygen

  scientists think approximately 2.7 billion years ago algae first evolved.

  > oxygen began to exist in the atmosphere

  the photosynthesis by primitive plants and algae allowed oxygen to build up in the atmosphere, until eventually it was high enough to allow animals to evolve
• decrease in carbon dioxide - formation of sedimentary rocks

  carbon dioxide is a very soluble gas

  it dissolves easily in water

  as the oceans formed, carbon dioxide dissolved in the water to form soluble carbonate compounds

  > amount of carbon dioxide in the atmosphere decreased

  carbonate compunds were then precipitated as sedimentary rocks

  eg: limestone
• decrease in carbon dioxide - organisms

  carbon dioxide was also asborbed from the oceans by algae and plants to use for photosynthesis

  many of these organisms and the simple organisms in the food chain (which they supported) were turned into fossil fuels which all contain carbon
• decrease in carbon dioxide - organisms

  coal

  coal was formed from trees, these trees were in dense forests, in low lying wetland areas

  flooding caused the wood from these trees to be buried in a way that prevented oxidation (allowing preservation)

  compression and heating over millions of years turned this wood into coal
• decrease in carbon dioxide - organsims

  crude oil and natural gas

  formed from simple, tiny plants and animals living in oceans and lakes

  these small organisms died and their remains were buried under sediments

  > lack of oxygen prevented oxidation from occuring (allowing for preservation)

  over millions of years heat and pressure turned them into crude oil and natural gas

  natural gas is often found on top of crude oil, trapped under sedimentary rock
• greenhouse effect

  it is a naturally occuring process needed to keep earth warm enough to aintain life, but human activities have made it worse

  greenhouse gases:

  • water
  • methane
  • carbon dioxide

  greenhouse gases

  • absorb heat radiated from earth
  • release energy in all directions (keeping earth warm)
• greenhouse effect

  1. electromagnetic radiation at most wavelengths passes through earth's atmosphere
  2. the earth absorbs most of the radiation ---> warms up
  3. earth radiates energy as infrared radiation
  4. some of the infrared goes back into space
  5. some is absorbed by greenhouse gases
  6. lower atmosphere warms up

  
• human activities are increasing the amount of greenhouse gases in the atmosphere:

  • farming cattle releases methane
  • farming rice in paddy fields releases methane
  • burning fossil fuels in vehicles and power stations releases carbon dioxide
  • deforestation releases carbon dioxide and reduces the amount of carbon dioxide absorbed by photosynthesis
• media and global warming

  When evaluating the quality of evidence on an issue like global warming, you should consider:

  • who did the research and whether they are trustworthy, skilled and experienced
  • who funded the research, because that might cause some bias
  • what methods were used to collect and analyse the data, because that might cause uncertainties in the evidence base
  • which organisation is reporting or publishing the evidence
• climate vs weather

  climate: average temperature and cycles of weather over long periods of time

  different to weather
• climate change

  earth's climate has been constantly changing including periods of heat and ice ages

  until 200 years ago these were caused by natural changes and changes in the amount of energy the earth recieves from the sun
• global warming

  global warming: the rise in the average temperature of the earth's surface and is caused now by human activities
• the strongest peice of evidence is the corrolation between the amount of carbon dioxide in the atmosphere (which correlates with human activity) and the global temperatures
• effects of global warming

  • glaciers and polar ice melting
  • sea levels rising
  • changes in pattern of rainfall, producing floods or droughts
  • habitats changing
• carbon footprint: the total amount of carbon dioxide (and other greenhouse gases) over a the full life cycle of a product, service or event
• combustion of hydrocarbon fuels

  most fuels contain hydrogen and or carbon and are hydrocarbons

  when hydrogen atoms are present in a fuel, they oxidise and form water, which is not a pollutant

  when there is sufficient amounts of oxygen, fuels burn and produce carbon dioxide, if there isn't sufficient oxygen they burn and produce carbon monoxide
• complete combustion

  happens when there is a good supply of oxygen

  the maximum amount of energy is released

  carbon dioxide and water are produced

  fuel + oxygen ---> carbon dioxide + water

  incomplete combustion

  happens when there isn't enough oxygen

  less energy is released

  carbon monoxide and water are produced

  fuel + oxygen ---> carbon monoxide + water
• problems with incomplete combustion

  • carbon monoxide binds to the haemaglobin in your red blood cells, preventing them from carrying oxygen
  • it is colourless and has no smell ---> hard to detect
  • particulate carbon irritates lining of the lungs which can worsen asthma and can cause cancer
  • particulate carbon also causes global dimming which may reduce rainfall
• sources of atmospheric pollutants

  carbon dioxide (CO2)

  source: complete combution of any fuel containing carbon

  carbon monoxide (CO)

  source: incomplete combustion of any fuel containing carbon

  particulate carbon, soot (C)

  source: incomplete combustion of any fuel containing carbon

  unburned hydrocarbons

  source: molecules of hydrocarbon fuel which have not been oxidised at all

  sulfur dioxide (SO2)

  source: combustion of any fuel containing sulfur impurities

  nitrogen oxides (NOx)

  source: oxidation of atmospheric nitrogen inside cars, lorrys ect
• sulfur dioxide

  produced when fuels containing sulfur are oxidised

  sulfur dioxide is then FURTHER oxidised in the atmosphere to make sulfur trioxide

  sulfur trioxide dissolves in water in the atmosphere to produce acid rain (H2SO4)

  acid rain:

  • harms and kills plants (especially those that live in aquatic environments)
  • damages manmade things like limestone statues and buildings
• nitrogen oxides

  nitrogen is not present in fuels, but high pressures and temperatures (like in a car engine) causes oxygen and nitrogen to react together and create nitrogen oxides

  we use NOx because there are many nitrogen oxides, and this groups them together

  nitrogen oxides:

  • causes acid rain
  • react with other pollutants in the atmosphere to make photochemical smog
  • smog has major health effects including asthma attacks and even death