Plate Tectonics

• There are two types of crusts on earth which are?

  Continental and oceanic
• Which type of crust is thicker and less dense?

  Continental crust
• How thick is the continental crust?

  20 - 70 km
• What is the continental crust mainly composed of?

  Granite
• Which type of crust is the most dense and less thick?

  Oceanic crust
• How thick is the oceanic crust?

  5 - 10 km
• What is the oceanic crust composed of?

  Basalt
• What are the ages of the different types of crusts?

  • Continental crust: Up to 4 billion years old
  • Oceanic crust: Up to 200 million years old
• Name the two layers within the upper mantle:

  Lithosphere

  Asthenosphere
• How are the upper and lower mantles different to one another?

  • The lower mantle is hotter and denser 
  • the lower mantle is solid
  • the upper mantles (asthenosphere) is semi-molten magma
• What is the asthenosphere?

  • The asthenosphere is a Semi-molten layer that constantly moves due to convection currents.
  • Movements are powered by heat from the core
  • The asthenosphere moves below the lithosphere causing plate tectonics to move
• The lithosphere consists of the crust and rigid upper section of the mantle
• The lithosphere is broken up into 7 major plates, which move around the Earth's surface
• What are the 4 main layers of the earth

  A) crust

  B) mantle

  C) outer core

  D) inner core

  
• The inner core is a solid ball made up of iron and nickel
• How hot is the inner core?

  Approximately 5200 degrees Celsius
• Why is the inner core so hot (5,200 degrees Celsius)?

  1. Radioactive decay (elements like uranium give off heat when they decay)
  2. Pressure
• The inner core is responsible for Earth's internal energy, and it spreads throughout the mantle
• The outer core is semi-molten and is made out of iron + nickel
• How hot is the outer core?

  Approximately 4500 - 5500 degrees Celsius
• Why do plates move due to the convection currents in the asthenosphere?

  the convection currents push and pull the plates in different directions; making them move
• Explain the cause of convection currents simply?

  Temperature differences in the magma create circular movements
• What does this diagram show?

  Convection currents in the mantle

  
• Name 2 pieces of evidence for the plate tectonic theory.

  1. Seafloor spreading
  2. Distribution of earthquakes and volcanoes
• What are the main 4 theories for what forces the tectonic plates to move?

  1. Ridge Push (gravitational sliding)
  2. Convection Currents
  3. Slab Pull (subduction zones)
  4. Mantle Drag (convection)
• Explain how Convection Currents work:

  1. Earth's mantel heats the inner part of the asthenosphere making it less dense and slowly rise
  2. As it rises to the top it cools down and becomes more dense making it slowly sink
  3. This creates circular movements of semi - molten rock which are the "convection currents"
• Shortly explain how "Slab pull" causes tectonic plates to move:

  Oceanic plates sink into subduction zones causing the sea floor to spread or rifts to form
• In detail explain how Slab pull causes tectonic plates to move:?

  1. At destructive margins, the new oceanic lithosphere is forced under the continental plate
  2. As the plates sinks, gravity pulls the plate down into the mantle
  3. This pulls slabs of plate apart
  4. Which causes the sea floor to spread or rifts to form (plate movement)
• In one word explain how "Mantle drag" causes plate tectonics to move:

  Convection
• In detail explain how "Mantle drag" causes plate tectonics to move:?

  the very slow creep-motion of convection currents in the mantle and asthenosphere drags the overlying solid lithosphere along like a conveyor belt
• Explain how "ridge push" moves plate tectonics:

  Gravitational sliding
• In detail explain how ridge push moves plate tectonics:?

  1. At constructive plate boundaries magma rises to the surface to form new oceanic crust which is very hot.
  2. The heat from the new crust heats up other surrounding rocks causing these rocks to expand and rise above the surface of the surrounding crust forming a slope
  3. The new crust then cools and becomes denser
  4. Gravity then causes the denser rock to move downslope away from the plate margin
  5. This puts pressure on the tectonics causing them to move apart <--__-->
• Fill in Blank:

  A) Mantle Drag

  
• Fill in Blanks:

  A) Slab Pull

  B) Subducting Slab

  
• Fill in Blank:

  A) Ridge Push

  
• Sea floor spreading:

  • Palaeomagnetism provides evidence that the sea floor has gradually moved apart at a mid-ocean ridge
  • Lava cools and solidifies with the minerals lining up with the magnetic field
  • The direction of the minerals on either side is a mirror image

  
• Slab pull can only occur at destructive plate boundaries
• Ridge Push can only occur at constructive plate margins
• What are mid ocean ridges?

  Underwater mountain ranges caused by the sea floor spreading apart
• What piece of evidence for the theory of plate tectonics did Alfred Wegner find?

  Fossil evidence and Pangea