1.4 Tectonic plates

• Alfred Wegener


  Suggested that all of the continents were once joined together in one supercontinent, called Pangaea, and that over millions of years they drifted apart
• Tectonic plates


  • The surface of the Earth is divided into a number of tectonic plates
  • These plates are constantly moving due to convection currents in the mantle
  • The movement of the plates causes the continents to move
• Evidence for continental drift


  • Fit of the edges of continents, e.g. the west coast of Africa and the east coast of South America
  • Similar rocks of the same age found on different continents
  • Similar plant and animal fossils found on opposite sides of huge oceans
• Wegener's theory did not include any attempt to explain how the continents moved and it was dismissed by more renowned scientists of the time</b>
• Convection currents in the mantle were proposed by some scientists as an explanation for plate movement as far back as the 1930s and this was generally accepted as being correct by the 1950s
• Wegener's theory of continental drift was refined and became known as plate tectonics
• Plate boundaries


  1. Conservative boundary: Plates move in opposite directions (side by side), overcome friction and move suddenly (earthquakes)

  2. Destructive boundary: Plates move towards each other, the denser plate sinks and melts, the less dense plate rises (forming mountains)

  3. Constructive boundary: As two plates move apart, magma rises into the gap and cools to form new igneous rocks
• Increase in deforestation and rise in the combustion of fossil fuels


  Increased levels of the gas carbon dioxide
• Increased levels of carbon dioxide

  Traps heat, leading to an increase in the average global temperature (global warming)
• Global warming is changing the climate, e.g. warmer summers in some parts of the world leading to droughts, and increased rainfall in other parts leading to flooding
• Personally, we can reduce the impact of global warming by using renewable sources of energy, reducing energy consumption at home, and using public transport
• Industry can reduce the impact of global warming through a process called carbon capture, which catches and stores carbon dioxide emissions
• Fractional distillation


  A process used to separate gases based on their different boiling points, similar to separating crude oil into fractions
• Tests to identify gases


  • Oxygen: Place in the presence of a glowing splint (relights the glowing splint)
  • Hydrogen: Place in the presence of a lit splint (makes a squeaky pop)
  • Carbon dioxide: Bubble the gas through limewater (limewater turns milky)
• Combustion of fossil fuels containing sulfur impurities


  Produces sulfur dioxide, which forms a solution of sulfuric acid when it comes into contact with water (acid rain)
• Acid rain has a pH of about 2 to 4 and can damage buildings, kill fish, and damage forests and vegetation
• Personally, we can reduce the effects of acid rain by using renewable sources of energy and neutralising affected soil and lakes
• Industrially, the effects of acid rain can be reduced through a process called sulfur scrubbing, where slaked lime (calcium hydroxide) is sprayed onto the smoke before it leaves the chimneys