earths atmosphere

• the first billion years of earth's history were pretty explosive - the surface was covered in volcanoes which erupted and released lots of gases. WE think this was how the early atmosphere was formed
• the early atmosphere was probably mostly carbon dioxide with virtually no oxygen. This is quite like the atmosphere of Mars and Venus today
• volcanic activity also released nitrogen which built up in the atmosphere over time as well as water vapour and small amounts of methane and ammonia
• when the water vapour in the atmosphere condensed it formed the oceans
• lots of carbon dioxide was removed from the early atmosphere as it formed the oxygen
• lots of carbon dioxide was removed from the early atmosphere as it dissolved in the oceans. This dissolved carbon dioxide then went through a series of reactions to form carbonate precipitates that formed sediments on the seabed
• green plants and algae evolved and absorbed some of the carbon dioxide so that they could carry out photosynthesis, later marine animals evolved. Their shells and skeletons contained carbonates from the oceans
• some of the carbon these organisms took in from the atmosphere and oceans became locked up in rocks and fossil fuels after the organisms died
• when plants plankton and marine animals die they fall to the seabed and get buried by layers of sediment. Over millions of years they become compressed and form sedimentary rocks, oil and gas - trapped the carbon within them and helping to keep carbon dioxide levels in the atmosphere reduced
• things like coal, crude oil and natural gas that are made by this process are called fossil fuels
• crude oil and natural gas are formed from deposits of plankton. These fossil fuels for reservoirs under the seabed when they get trapped in rocks
• coal is a sedimentary rock. Its mostly made of calcium carbonate deposits from the shells and skeletons of marine organisms
• As well as absorbing the carbon dioxide in the atmosphere green plants and algae produced oxygen by photosynthesis
• algae evolved first - about 2.7 billion years ago then over the next billion years or so green plants also evolved
• eventually 200 million years ago the atmosphere reached a composition similar to what it is like today 80% nitrogen and 20% oxygen and small amounts of other gases (each only makes up less than 1% of the earths atmoshere)
• green house gases like carbon dioxide, methane and water vapour act like an insulating layer in the earths atmosphere - this amongst other factors allows the Earth to be warm enough to support life
• All particles absorb certain frequencies of radiation. Greenhouse gases don't absorb the incoming short wavelength radiation from the sun - but they do absorb the long wavelength radiation that gets reflected back off the earth. Then they re-radiate it in all directions - including back towards the earth. The long wave radiation is thermal radiation so it results in warming of the surface of the earth this is the green house gas effect
• some forms of human activity affect the amount of greenhouse gases in the atmosphere what are they

  • deforestation - fewer trees means less carbon dioxide is removed from the atmosphere via photosynthesis
  • burning fossil fuels - carbon that was locked up in these fuels is released as carbon dioxide
  • agriculture - more farm animals produce more methane through their digestive processes
  • creating waste - more landfill sites and more waste from agriculture means more carbon dioxide and methane released by decomposition
• the earth's temperature varies naturally but recently the average temperature of the earth's surface has been increasing. Most scientists agree that the extra carbon dioxide from human activity is causing this increase and that this will lead to climate change
• evidence for this has been peer-viewed so you know that the information out there is reliable
• dangerous consequences of climate change

  • an increase in global temperature could lead to polar ice caps melting - causing a rise in sea levels, increased flooding in costal areas and coastal erosion
  • changes in rainfall patterns may cause some regions to get too much or too little water. This, along with changes in temperature may affect the ability of certain regions to produce food
  • the frequency and severity of storms may also increase
  • changes in temperature and the amount of water available in a habitat may affect wild species leading to differences in their distribution
• Carbon dioxide is a very soluble gas. It dissolves readily in water. As the oceans formed, carbon dioxide dissolved to form soluble carbonate compounds so its amount in the atmosphere decreased. Carbonate compounds were then precipitated as sedimentary rocks, eg limestone.
• Describe two reasons why the amount of carbon dioxide in the atmosphere decreased over time.

  Carbon dioxide dissolved in the oceans, and primitive plants used it for photosynthesis.