Geo

• Governments act rationally by


  Placing the interests of the people they serve first in order to maximise their welfare
• Rationality in classical economic theory is a flawed assumption as people usually don't act rationally
• Marginal utility


  The additional utility (satisfaction) gained from the consumption of an additional product
• Earth's core


  Can be divided into a liquid outer core and an iron-rich solid inner core. Temperatures here are extremely hot (5,500°C).
• The centre of the Earth is 6,400 km below the surface
• Components of the Earth's structure


  • Continental crust
  • Oceanic crust
  • Mantle
  • Outer core
  • Inner core
• Oceanic crust (sima)


  • Continuous around the Earth's surface, mostly made of basalt where silica (si) and magnesium (ma) are dominant
• Continental crust (sial)


  • Discontinuous around the Earth and less dense, comprising rocks such as granite where silica (si) and aluminium (al) dominate
• The Earth's crust is broken into several large sections called plates
• Plates


  • Each plate is about 100 km thick and is made up of the crust and the upper part of the mantle. The solid plates rest on a semi-liquid layer in the upper mantle and this enables them to move in relation to each other.
• Types of plate boundaries

  • Divergent
  • Convergent
  • Collision
  • Transform
• What causes the plates to move

  1. Heat spreads out and flows towards the surface forming convection (heat) cells

  2. Convection currents rise from deep in the mantle and move towards the surface

  3. They then spread below the crustal plates, cool and finally descend back down into the mantle
• Some 250 million years ago the continents of the world were joined together to form one enormous continent called Pangaea
• Evidence for continental drift

  • Identical rocks in South America and West Africa
  • Continents fit together like a jigsaw puzzle
  • Identical land-based fossils found in separated continents
  • Rocks on the ocean floor become steadily older the further they are from the middle of the ocean
• During the 1960s and 1970s further scientific evidence led to a greater understanding of convection currents and of the mechanisms involved in plate tectonics
• Patterns of earthquakes, volcanoes, mountain ranges and deep ocean trenches provided evidence of the precise location of the active plate boundaries

  
• Scientists are still developing their understanding of the theory of plate tectonics in the light of recent earthquakes and volcanic activity

  
• Divergent plate boundary


  Two plates are moving away from each other, new crust is being formed
• Features of a divergent plate boundary

  • Mid-Atlantic Ridge
  • Islands such as Iceland and the Azores
• What happens at a divergent plate boundary


  1. Rising convection current causes the crust to crack, allowing molten rock (magma) to pass through

  2. Magma escapes to the surface as lava erupted from underwater volcanoes, forming a mid-oceanic ridge

  3. New plate material forms at the mid-oceanic ridge, plates extend outwards and diverge
• Convergent plate boundary


  Two plates are moving towards one another, one plate dives down beneath the other plate to form a subduction zone
• Features of a convergent plate boundary

  • Peru-Chile deep-sea trench (subduction zone)
  • Andes (fold mountains)
• What happens at a convergent plate boundary

  1. Denser oceanic crust dives down beneath less dense continental crust

  2. Friction along the plate margin triggers earthquakes

  3. Oceanic crust melts and magma forces its way to the surface to form volcanoes

  4. Crumpling of sea-floor sediments creates fold mountains
• Collision plate boundary


  Two plates of continental crust converge, layers in the seabed crumple to form fold mountain ranges
• Example of a collision plate boundary


  • Himalayas
• Powerful earthquakes are triggered by the cracking of rocks at collision plate boundaries
• There are no volcanoes at collision plate boundaries due to the lack of subduction
• Transform plate boundary


  Two plates are sliding alongside each other, no subduction or creation of magma
• Example of a transform plate boundary


  • San Andreas Fault
• Earthquakes are very common at transform plate boundaries

  
• The 1906 San Francisco earthquake was caused by the San Andreas Fault suddenly lurching by 6 m

  
• Caribbean plate

  Much of the Caribbean region lies on the Caribbean plate, its boundaries are extremely active as it is being squeezed by converging plates on either side
• Boundaries of the Caribbean plate

  • Northern edge - transform boundary with North American plate
  • Western boundary - oceanic Cocos plate subducting beneath Caribbean plate
  • Southern boundary - part convergent, part transform
• The 2010 Haiti earthquake was caused by the transform boundary between the Caribbean plate and the North American plate
• Lesser Antilles volcanic arc

  Chain of mostly volcanic islands formed at the convergent boundary where the South American plate is subducting beneath the Caribbean plate
• Islands in the Lesser Antilles volcanic arc

  • Montserrat
  • Guadeloupe
  • Dominica
  • Martinique
  • St Lucia
• Many of the volcanoes in the Lesser Antilles have erupted violently in the past, such as Mt Pelee on Martinique in 1902 and Soufriere Hills on Montserrat in recent years
• Kingston, Jamaica has been struck by powerful earthquakes in the past, such as in 1692 and 1907
• Earthquake


  A sudden violent shaking of the ground, originating from a focus point within the crust and radiating outwards as seismic waves
• The point on the ground surface immediately above the earthquake focus is called the epicentre