Earth physics

• When a bell is struck, the sound is due to the metal vibrating
• Sound

  A wave
• Sound is the travelling disturbances (compressions and rarefactions) in air or another medium caused by a vibrating object
• A sound can only be heard if the disturbances arrive in our ears causing our ear drums to vibrate
• Periodic disturbances


  Travelling regular disturbances in a medium
• A vibrating source inside a medium produces a sound wave in the medium
• A wave transfers energy from one place to another without transferring matter
• Medium


  Sound can travel in all types of materials, solids, liquids or gases, not just air
• Dolphins and whales communicate inside the water by emitting sounds
• Sound travels faster in liquids and in solids

  Than in gases
• Earth's major tectonic plates

  • Continental plates
  • Oceanic plates
• Evidence of moving plates


  Sea floor spreading
• As from the 1960s new data began to support the idea of continental drift
• The data came primarily from the study of seafloors
• Maps of the ocean floor showed massive undersea mountain ranges, called oceanic ridges
• Oceanic ridges almost circled the entire Earth
• Molten rock (magma) rises from the mantle


  Creates oceanic ridges
• Magma


  Molten rock that is underground
• Lava


  Molten rock that breaks through the Earth's surface
• Theory of Plate Tectonics

  The entire surface of the Earth is a mosaic of plates, without gaps
• Plate boundaries


  Where tectonic plates interact
• Plates moving apart


  1. Formation of ridges

  2. Formation of rift valleys
• Earthquakes are common where plates move apart, but they are weak and shallow
• Plates sliding past each other

  1. Creates transform faults

  2. Rocks are pulverised

  3. Plates lock together

  4. Built-up stress causes rock to break
• Strong earthquakes are characteristic and common at transform fault boundaries
• Transform faults do not cause formation of special geological features like mountains or volcanoes
• Plates colliding


  1. Oceanic plate collides with continental plate

  2. Continental plate collides with continental plate

  3. Oceanic plate collides with oceanic plate
• Oceanic plate collides with continental plate

  Causes subduction and formation of fold mountain ranges
• Continental plate collides with continental plate


  Causes buckling and formation of fold mountains
• Oceanic plate collides with oceanic plate

  Causes subduction and formation of volcanic islands
• Subduction


  Denser oceanic plate dives down under the lighter plate and sinks into the mantle
• Subduction causes the destruction of crust
• Subduction

  When the denser oceanic plate dives down under the lighter plate and sinks into the mantle beneath, where it melts
• Subduction causes the destruction of crust
• Subducting plate sinks into the mantle

  Causes earthquakes and fold mountains
• Magma


  Liquid rock inside a volcano
• Lava


  Liquid rock that flows out of a volcano
• A deep ocean trench forms where an oceanic plate dives down under another plate
• Such trenches are the deepest parts of the oceans
• The Marianas Trench in the Pacific Ocean is the deepest trench, with measured depths of over 11 km below sea level