UNIT 4 ATMOSPHERE

• Producer


  Make their own food by photosynthesis using carbon dioxide
• Greenhouse gas


  Gases that absorb infra-red radiation that is reflected off the Earth
• Climate


  Long-term patterns of weather
• Potable water


  Water that is drinkable
• Earth formed 4.6billion years ago so there is limited evidence about the composition of its early atmosphere (there is no primary evidence from this time)
• One theory about the early atmosphere: volcanoes released gases (including water vapour that condensed to form the oceans); the most abundant gas was carbon dioxide and there was little or no oxygen (just like Mars and Venus today)
• Volcanoes also produced nitrogen which gradually built up and there may have also been small amounts of ammonia and methane
• CO2 levels decreased because: CO2 dissolved in the oceans (forming carbonates); plants and algae evolved and took in CO2 by photosynthesis; CO2 was used in the formation of sedimentary rocks and fossil fuels
• O2 levels increased when plants and algae evolved and released O2 by photosynthesis – when oxygen levels were high enough, animals were able to evolve
• All living things respire, which releases CO2 into the atmosphere
• Decay of dead plants and animals returns carbon to the atmosphere (as decomposers respire) and mineral ions to the soil
• Greenhouse gases (carbon dioxide, methane and water vapour) allow short-wavelength radiation to pass from the sun to Earth, but absorb the long-wavelength radiation that is emitted from the Earth's surface
• Burning fossil fuels adds carbon dioxide to the atmosphere – there is a correlation between this and the rise in Earth's temperature
• Scientists cannot be certain about the future of our climate because they have to make predictions about future greenhouse gas emissions and because the many complex changes on Earth can affect climate
• The consequences of global warming are: sea-levels rising, loss of habitats, changes to weather extremes, changes in the amount, timing and distribution of rainfall, temperature and water stress for humans and wildlife, changes in species distribution, changes in the food-producing capacity of some regions
• Steps to reduce climate change are: using energy resources more efficiently, using renewable resources, reducing waste by recycling, stopping deforestation, regenerating forests, developing carbon dioxide capture and storage techniques
• Acid rain damages plants and buildings and harms living organisms in ponds, rivers and lakes
• Water is found in 3 states on Earth: solid state (in ice sheets and glaciers), liquid state (lakes, rivers, oceans and aquifers) and the gas state (water vapour in the atmosphere)
• Water is important for life because: it acts as a solvent for chemical reactions in cells; it helps transport dissolved compounds into and out of cells; water is either a reactant or a product in biochemical changes e.g. respiration, photosynthesis and digestion; rivers, lakes and seas provide habitats
• Freshwater (from the rain) must be filtered (to remove solid matter( and sterilised (to kill bacteria) using ozone, chlorine or UV light before drinking
• Salty water must be desalinised by distillation or by reverse osmosis (this requires large amounts of energy)
• Waste water must be treated by: screening (grit removal); sedimentation (forming sludge that we use anaerobic bacteria to clean, and can then be used as a fuel); useful bacteria feed on any harmful organic matter in the water; the useful bacteria are left to settle (form sediment); the water is filtered and sometimes sterilised before being released back into rivers
• Carbon monoxide (CO)


  Toxic gas, formed from the incomplete combustion of fossil fuels, combines to haemoglobin in our red blood cells so less oxygen can be carried (causes heart strain at low doses and death at high doses)
• Sulfur dioxide (SO2)


  Formed when fuels containing sulfur impurities are burnt, leads to respiratory problems and acid rain
• Oxides of nitrogen (NOx)


  Formed when oxygen and nitrogen from the air react (due to high temperatures), causes respiratory problems and acid rain
• Soot (C)


  From diesel engines, goes into people's lungs and can lead to heart disease and lung cancer