Plate Tectonics

• Distinct boundaries of the Earth's crust
• Explains how slow motions within Earth's mantle move large segments of the crust
• Results in a gradual drifting of the continents
• Forms mountains and other large-scale geological features
• Cooling system for the planet
  • Heat from inside --> outside
• There are ~12 tectonic plates on Earth
• Plates are moved by convection of the mantle
• Four basic interactions between plates at their boundaries
  • Pull apart (rift zone)
  • One plate burrows under another (subduction zone)
  • Slide alongside each other (fault zone)
  • Jam together
• Constantly renews Earth's crust and erases cratering events

Rift and Subduction Zones

• Rift zones
  • Plates pull apart from each other
  • Most found in the oceans
• Subduction zones
  • Two plates come together, one is forced beneath another
  • Thinner oceanic plates can be readily thrust down into upper mantle
  • Often marked by ocean trenches

Fault Zones

• Crustal plates sliding parallel to each other
• Marked by cracks or faults
• Motion builds up stresses in the crust and released in sudden, violent slippages
  • This generates earthquakes
  • The longer the interval between earthquakes, the greater the stress and more energy released when the surface finally moves

Geology Earth