Geomagnetism

• which waves are labelled as P?

  P waves in the mantle
• which waves are labelled as S?

  S waves in the mantle
• which waves are labelled as K?

  P waves in the outer core
• which waves are labelled as I?

  P waves in the inner core
• which waves are labelled as J?

  S waves in the inner core
• which waves are labelled as c?

  reflection off outer core
• which waves are labelled as i?

  reflection off inner core
• which type of wave does the main P wave shadow zone contain?

  weak P arrivals with long travel times
• what do S waves reappear from the shadow zone as?

  transformed P waves
• how much of earth's mass does the crust account for?

  less than 0.5 %
• how much of earth's mass does the mantle account for?

  two thirds
• how much of earth's mass does the core account for?

  one third
• what is the earth's core mainly made of?

  iron
• what can be found in the outer core?

  higher proportions of lighter elements such as nickel, sulphur and oxygen
• what is the main evidence for the iron rich core?

  magnetism
• why is the iron core growing?

  as earth cools the molten iron in the outer core is freezing
• what are the three fields that provide evidence for the composition of earth's core?

  geochemistry, geomagnetism and geophysics
• what does the magnetic field strength vary with?

  latitude
• where is the magnetic field the strognest?

  the magnetic poles
• where is the magnetic field the weakest?

  the magnetic equator
• how long does the magnetic field reversal process take?

  400 years
• why does the magnetic field reverse?

  because of major changes in core convection pattern
• how is the geomagnetic field generated?

  convection currents in an electrically conducting metallic liquid in the outer core which acts as a self exciting dynamo
• what is a dynamo which proceeds a magnetic field around itself called?


  a self exciting dynamo
• why is permanent magnetism not possible on earth?

  earth's interior is too hot