Unit 3 topic 1

• Plate boundaries


  Global pattern of plate boundaries (world map knowledge is useful), different types of plate boundaries, why they occur and the processes that operate there
• Subduction


  Process where one plate is forced under another plate
• Seafloor spreading


  Process where new crust is formed at mid-ocean ridges

  
• Landforms formed at plate boundaries


  • Describe and explain the landforms formed at plate boundaries
• The Earth formed due to collisions between clouds of dust and gas

  4.6 billion years ago
• The earliest life is believed to have formed

  4 billion years ago
• Photosynthesis started


  3.5 billion years ago
• Multicellular life is believed to have formed

  1.5 billion years ago
• The systematic study of the Earth began

  300 years ago
• Geoid

  The Earth is not a perfect sphere, it bulges slightly around the equator and is flatter at the poles
• Centrifugal forces

  Forces generated by the Earth's rotation that fling the semi-molten material outwards
• Types of crust


  • Oceanic
  • Continental

  
• Oceanic crust


  • 5-10km thick, younger (65 million years old), denser, made of basaltic rocks (SIMA)

  
• Continental crust


  • Up to 70km thick, older (up to 1.8 billion years old), less dense, made of granite rocks (SIAL)

  
• Intrusive rocks


  Magma cools, crystallises and solidifies below the surface, forming coarse-grained igneous rocks like granite

  
• Extrusive rocks


  Magma cools, crystallises and solidifies with air or sea, forming fine-grained igneous rocks like basalt
• Mantle


  The thickest layer of the Earth, 2900km thick, made up of mainly lighter elements - silicate rocks, in a thick liquid state - molten and semi-molten
• Asthenosphere


  A softer plastic-like layer in the upper mantle, can move very slowly, carrying the lithosphere
• Lithosphere


  The upper section of the mantle and the crust, 80-90km thick, divided into seven very large plates and several smaller plates

  
• Core


  The hottest layer of the Earth, 5000°C, made of iron and nickel, 4 times as dense as the crust
• Outer core


  Semi-liquid, mainly iron, 2250km thick
• Inner core


  Solid ball made up of iron & nickel, 1900km thick
• Earth's magnetic field


  Thought to be created by the spinning of the liquid outer core
• Seismic waves


  Waves that travel through liquid and solids at different speeds, used to study the Earth's interior

  
• Primordial heat


  Heat energy left over from the formation of the Earth 4.6 billion years ago
• Radioactivity


  Natural radioactive decay of uranium, thorium and potassium provides a continuous but slowly diminishing heat supply within the Earth
• Convection currents


  Currents generated by the heat within the asthenosphere, which help move the plates
• Pangaea


  The single supercontinent that existed 300 million years ago, which later split into Laurasia and Gondwanaland
• Wegener's evidence for plate tectonics


  • Shape of continents
  • Glacial evidence
  • Rock evidence
  • Climatological evidence
  • Biological evidence

  
• Wegener's theory could not explain how the continents moved, so it gained little support initially

  
• Sea floor spreading


  The process where new crust is formed at mid-ocean ridges

  
• Paleomagnetism


  The regular pattern of magnetic striping discovered on either side of mid-ocean ridges, which suggests new rocks are added equally to each side

  
• Ocean trenches


  Huge depressions in the ocean floor where oceanic crust is subducted (sliding) under continental crust

  
• Hotspots


  Stationary points in the Earth's mantle where magma rises to the surface, causing volcanic activity

  
• Convection currents in the mantle, caused by high temperatures at the core, help move the tectonic plates
• Oceanic plate


  Forced into the mantle, melts under pressure, consumed
• Continental crust


  Not consumed
• Landforms at subduction zones


  • Accretionary prism
  • Volcanic arc
  • Ocean trench
  • Oceanic crust
  • Asthenosphere
  • Lithosphere
  • Subduction zone
  • Rising diapirs
  • Magma chamber
  • Moho discontinuity
  • Continental crust
  • Solid uppermost mantle

  
• Convection currents


  Hot rocks rise towards crust, cool and sink, creating current
• Satellites use lasers and GPS to measure and track plate movements as small as a few mm