Restless Earth

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The Structure of the Earth


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  • Split into tectonic plates (7 major plates)
  • Thinnest layer
  • 2 types - Oceanic and Continental


  • Found under oceans, approx 5-10 km thick
  • Made up of things like basalt
  • Relatively young, oldest only around 180 million years old
  • Dense so sinks into mantle when it meets with continental
  • Constantly forms at constructive boundaries, destroyed at destructive boundaries


  • Found under land, approx 25-100km thick
  • Very old, 3-4 billion years old
  • Not very dense so doesn't sink into mantle
  • New crust not formed in this type but not destroyed either


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Mantle & Core


  • Made up of magma (soft molten rock)
  • Can be up to 5000 degrees celcius
  • Approx 3800 degrees celcius

Outer Core

  • Only liquid layer
  • Roughly 1,400 miles thick
  • Mainly iron and nickel

Inner Core

  • Very hot - can be up to 5500 degrees celcius
  • Solid
  • Very dense
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Tectonic Plates

Why do plates move?

- Due to convection currents

Convection currents - how do they work?/what do they do?

1. Magma rises towrds the crust

2. Magma reaches the crust but doesn't break through

3. Friction occurs between magma and the crust causing the plates to slowly move

4. Magma cools down and sinks, then warms up again.

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Plate Boundaries/Margins


  • Plates pull apart - convection currents
  • Creates gap, allows magma fron mantle to rise through
  • As more magma rises it builds up to create new crust
  • New crust builds up to create volcano
  • As magma rises there can be gentle earthquakes


  • Mid Atlantic Ridge
  • Eurasian and North American plates
  • Volcano also formed small island (Iceland)
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Plate Boundaries/Margins


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Plate Boundaries/Margins


  • Plates move past each other - convection currents - creates friction
  • May move at different speeds causing pressure and friction to build up
  • Eventually pressure releases causing earthquake
  • Volcanoes not created at these boundaries


  • San Andreas Fault, California
  • North American and Pacific plates
  • NA moves 1cm/year, P moves 6cm/year
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Plate Boundaries/Margins


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Plate Boundaries/Margins


  • Oceanic and Continental plates collide
  • Oceanic plate denser, subducts under Continental
  • Sinks into mantle, melting into magma as it does this
  • As plate sinks, so does seawater - magma formed less dense than mantle
  • Eventually rises up through continental plate & explodes at surface as volcano
  • Trapped seawater becomes steam - extremely explosive volcano
  • Not much lava, lots of ash, steam and gas
  • Earthquakes due to friction when plate sinks
  • As C plate moves towards O plate land on plate edge crumpled, fold mountains formed


  • The Andes
  • Fold mountains
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Plate Boundaries/Margins


  • 2 Continental plates meet
  • Same density - neither subducted into mantle
  • Plates continue to push together, pressure builds up
  • Eventually release causing plates to crumple into each other
  • Land between pushes up - fold mountains formed
  • No volcanoes formed
  • Earthquakes created due to friction when plates push together


  • Himalayas
  • Fold mountains
  • Indo-Australian and Eurarsian plate colliding
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Plate Boundaries/Margins


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Plate Boundaries/Margins


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