C9 Revision - Chemistry of the Atmosphere

  • Created by: Benny52
  • Created on: 22-10-18 12:22

The Evolution of the Atmosphere

Phase 1 - Volcanoes gave out gases (Nitrogen, Water Vapour, Methane, Ammonia)

  • 1st billion yrs of Earth's history - Explosive. Surface covered in volcanoes
  • Mostly CO2, with virtually no oxygen - like atmospheres of Venus & Mars today.

Phase 2 - Oceans, Algae and Green plants absorbed CO2 

  • When water vapour condensed, it formed oceans. Lots of CO2 removed - dissolved in oceans. Dissolved CO2 went through series of reactions to form carbonate precipitates - formed sediments on seabed.
  • Green plants and algae evolved & absorbed some of CO2 - photosynthesis. Later, marine animals evolved. Their shells & skeletons contained carbonates from oceans.
  • Some of carbon these organisms took in become locked in rocks and fossil fuels after organisms died.
    • When plants, plankton and marine animals die, they fall to seabed and get buried by layers of sediment. Over millions of years, they become compressed - form sedimentary rocks, oil & gas - trapping carbon within them anh helping keep CO2 levels in atmosphere reduced. Fossil fuels made by this process.
    • Crude oil & natural gas formed by depositis of plankton. These fossil fuels form reservoirs under seabed when they get trapped in rocks
    • Coal - sedimentary rock made from thick plant deposits. Limestone - sedimentary rock mostly made of calcium carbonate deposits from shells and skeletons of marine organisms.
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The Evolution of the Atmosphere 2

Phase 3 - Green plants and Algae produced O2 - Photosynthesis - when plants use light to convert CO2 & water to sugars: Carbon dioxide (6CO2) + Water (6H2O) --> Glucose (C6H12O6) + Oxygen (6O2)

  • Algae evolved 1st - about 2.7bn years ago. Over next bn years, green plants evolved.
  • As O2 levels increased, more complex life (animals) could evolve.
  • 200mn yrs ago, atmosphere reached composition similar to today's - approx 80% nitrogen, 20% oxygen and other gases (each less than 1%) - mainly CO2, noble gases and water vapour.
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Greenhouse Gases and Climate Change

  • Greenhouses gases (e.g. CO2, CH4 & water vapour) act like insulating layer in atmosphere - factor that allows Earth to be warm enough - support life.
  • Greenhouse gases dont absorb short wavelength radiation from sun - absorb long wavelength reflected back off Earth. Re-radiate it in all directions - including back towards Earth. Long wavelength radiation - thermal radiation - warming of surface of Earth - Greenhouse effect
  • Human activities which affect amount of greenhouse gases in atmosphere:Average temp. of Earth's surface increasing - Scientists - extra CO2 from human activity - Climate ChangeEarth's climate - complex - so many variables - hard to make simplified model - lead to speculation (mainly media) where stories are biased or not all info is given. Evidence for climate change - peer reviewed - reliabe
    • Deforestation: fewer trees - less CO2 removed from atmosphere - photosynthesis
    • Burning fossil fuels: Carbon 'locked up' in fuels released as CO2
    • Agriculture: More farm animals - more methane through digestive processes
    • Creating waste: more landfills + agricultural waste - more CO2 & methane from decomposition of waste.
  • Consequences of climate change:
    • Polar ice caps melting - rise in sea levels - increased flooding in coastal areas and coastal erosion.
    • Changes in rainfall patterns - regions have too much/little water. Along with temp., may affect ability of certain regions to produce food.
    • Frequency + severity of storms - increase
    • Changes in temp & amount of water available in habitat - affect wild species distribution 
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Carbon Footprints

  • Measure of amount of CO2 and other greenhouse gases over full life cycle of something.
  • Measuring - hard - many factors. Rough calculation give good idea of worst emitters.
  • Can reduce carbon footprint:
    • Renewable enegry sources/nuclear energy instead of fossil fuels
    • Using more efficient processes - save energy & cut waste
    • Government tax companies/individuals based on greenhouse gases emissions - fuel-efficient options used. Can also put cap on emissions of greenhouse gases companies make - sell licences for emissions up to that cap.
    • Technology that captures CO2 from burning fossil fuels before released - stored deep underground in cracks in rock - old oil wells.
  • Hard to reduce - lot of work to be done on alternative technologies
  • Lot of governments worried making changes will impact economic growth of communities - bad for people's well-being - important for developing countries.
  • Not everyone's on board - international agreements hard to reduce emissions. Most countries don't want to sacrifce economic development if they think others won't do the same.
  • Individuals in developed countries need to make changes lifestyles. Hard to get people to make changes if they don't want to and if there isn't enough education provided as to why changes are necessary and how to make them
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Air Pollution

  • Fossil fuels contain hydrocarbons. During cumbostion, H & C oxidised - CO2 and water vapour released into atmosphere
  • Plenty of O2, all fuel burns - complete combustion. Not enough O2, some fuel doesn't burn - incomplete combustion. Solid particles (particulates) of soot - carbon - and unburnt fuel released & CO  + CO2 produced.
  • Particulates:
    • If inhaled, can get stuck in lungs & cause damage - lead to respiratory problems
    • Bad for environment. They or clouds they help produce reflect sunlight back into space. Less light reaches Earth - global dimming.
  • Carbon Monoxide:
    • Dangerous - stops blood from carrying oxygen round body. Binds to haemoglobin in blood that carries O2 - less O2 transported - lack of oxygen - fainting, coma, death
    • No smell, colour - hard to detect - more dangerous.
  • SO2 released - combustion of fossil fuels that contain sulfur impurities - sulfer oxidised
  • N oxides created from reaction between nitrogen & oxygen in air, caused by heat of burning - happenes in internal combustion engines of cars.
  • When these gases mix with clouds, they form dilute sulfuric/nitric acid - falls as acid rain - kills plants and damages buildings and statues. Makes metal corrode.
  • SO2 and nitrogen oxides - respiratory problems if breathed in. Bad for health.
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