The Mid-Atlantic Ridge

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• The Mid-Atlantic Ridge
• By Amy Garrison
• G355
• May, 2009

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The plate

• Plate Tectonics - quick review
• The theory that the Earths surface is broken
  into a number of thick plates that are slowly and
  continuously moving
• This contributes to Continental Drift

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The plate tectonics theory was first proposed by
Alfred Wegener, a German meteorologist, in
1912 It is the concept that the Earths crust
is composed of rigid plates that move over a
less rigid interior.
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There are 3 different kinds of boundaries where
2 plates come together Divergent which is
what the mid-atlantic ridge is, Convergent and
Transform.
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A divergent boundary is where two different
plates are moving in opposite directions -
away from each other. New crust is
created as the old crust moves away,
similar to a conveyor belt.
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• In the case of the mid-Atlantic ridge, a
  mountain range was formed from this
  process.
• It is located along the floor of the
  Atlantic Ocean and is the longest mountain
  range in the world.
• It separates the Eurasian Plate from the
  North American Plate in the North Atlantic,
  and the African Plate from the South American
  Plate in the South Atlantic.
• It extends from a junction with the Mid-Arctic
  Ridge, northeast of Greenland southward, to the
  Bouvet Triple Junction in the South Atlantic.
• These plates are still moving apart, so the
  Atlantic is growing at the ridge at a rate of
  about 2.5cm per year, in an east-west direction.

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• While the Mid-Atlantic Ridge is mostly an
  underwater feature, there are portions of it that
  have enough elevation to extend above sea level.
  
• Some of the islands that have been created and
  are part of this ridge are Iceland, the Azores,
  Bermuda, and Saint Peter and Paul Rocks.

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A fissure running along the Mid-Atlantic Ridge
in Iceland
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• An important discovery that has to do with
  sea-floor spreading
• Ocean floor magnetism and magnetic reversals
• Did you know that about every half million, years
  the Earths magnetic polarity reverses ??
• So does the magnetization of the ocean floor.

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• Magnetic Reversals
• Molten lava emerges from volcano
• Solidifies to a rock usually (black) basalt
• Basalt is faintly magnetic, like iron.
• Its magnetization is in the direction of the
  local magnetic force at the time when it cools
  down.    
• Instruments can measure the magnetization of
  basalt.

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• Suggested that times existed when the
  magnetization had the opposite direction from
  today's.
• In the end it was determined that in the distant
  past, the magnetic polarity of the Earth was
  sometimes reversed.
• Magnetization in the ocean was orderly, arranged
  in long strips.
• Strips on the Atlantic ocean floor, in
  particular, all seemed parallel to the
  "mid-Atlantic ridge." 
• Not only were the magnetic strips lined-up with
  the central ridge,
• Their structure and distribution seemed
  remarkably symmetric on both sides

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• As "plates" on each side are pulled away,
• Lava emerges from the middle, solidifies and
  "records" the prevailing magnetic field.
• The newly formed basalt sticks to the plates and
  is also pulled away
• Every half million years, on the average, the
  Earth's magnetic polarity reverses, and so does
  the magnetization of the ocean floor.
• Each strip represents an epoch of one or the
  other magnetic polarity, and the symmetry is also
  explained.
• The sea-floor is a giant tape recorder, with twin
  tapes emerging from the mid-Atlantic ridge
• Similar magnetic strips were also observed in all
  other oceans.

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• Lab
• Information credits
• http//www.google.com/search?hlendeflenqdefin
  eplatetectonicseicb4QSsqgIKL6tQPV17znCwsaXo
  iglossary_definitioncttitle
• http//en.wikipedia.org/wiki/Mid-Atlantic_Ridge
• http//www.google.com/imgres?imgurlhttp//www.iki
  .rssi.ru/mirrors/stern/earthmag/Figures/wegener.gi
  fimgrefurlhttp//www.iki.rssi.ru/mirrors/stern/e
  arthmag/reversal.htmh304w216sz29tbnideWzDj
  XMBhF5MvMtbnh116tbnw82prev/images3Fq3Dim
  age2B2Bof2B2BAlfred2BWegenerhlenusg__5izJ
  RZ-nvCQrrYYUvrcw4lpYf0geit8AQSsTPBYOKtAO3ibj3Ag
  saXoiimage_resultresnum4ctimage
• Photo credits
• http//whc.unesco.org/en/activities/504/
• http//www.iki.rssi.ru/mirrors/stern/earthmag/Figu
  res/wegener.gif
• http//en.wikipedia.org/wiki/Mid-Atlantic_Ridge
• http//www.epm.geophys.ethz.ch/cfinlay/Images/cor
  e_cut.jpg
• http//www.nature.nps.gov/geology/usgsnps/pltec/vi
  gil595x266lab.jpg
• http//www.google.com/search?hlendeflenqdefin
  eplatetectonicseicb4QSsqgIKL6tQPV17znCwsaXo
  iglossary_definitioncttitle
• http//www.mysciencebox.org/seafloor
• http//www.google.com/imgres?imgurlhttp//www.a3b
  s.com/imagelibrary/U19550/electricity-and-magnetis
  m/U19550_pair-of-bar-magnets-80-mm.jpgimgrefurlh
  ttp//www.a3bs.com/shop/u.s.a./electricity-and-mag
  netism/magnetism,pg_83_671_623_0.htmlh438w400
  sz26tbnid5_erY2DpNAoZdMtbnh127tbnw116pre
  v/images3Fq3Dimages2Bof2Bmagnetshlenusg__
  KVEICqH0EQSLrBnBhyUfANR44v8eiIuQRSueBJI78swOn2M
  jyDQsaXoiimage_resultresnum4ctimage
• http//www.google.com/imgres?imgurlhttp//www.pla
  tetectonics.com/oceanfloors/images/Africa-South_Am
  erica_4.jpgimgrefurlhttp//www.platetectonics.co
  m/oceanfloors/africa.asph260w245sz17tbnid2
  nSSaPr8WOzrDMtbnh112tbnw106prev/images3Fq
  3Dimages
• http//www.windows.ucar.edu/teacher_resources/magn
  etism/mid_atlantic_ridge_10_inch.jpg