Magnetic Striping

• Earth has a geographic North & South, and magnetic North & South
• Geographic North & South does not change
• Magnetic North & South can shift, and they have reversed multiple times
• Normal polarity

  Magnetic North points roughly towards geographic North, and Magnetic South points towards geographic South
• Reverse polarity

  Magnetic North points roughly towards geographic South, and magnetic South points roughly towards geographic North
• Magnetic striping is the zebra-like pattern where there are strips of normal polarity rocks alternating alongside strips of reverse polarity rocks on the seafloor
• The zebra-like pattern is symmetrical on both sides of the mid-ocean ridge
• Occurrence

  • Basaltic rocks from oceanic crust are volcanic rocks formed from iron-rich lava
  • They contain magnetic materials
  • When iron-rich lava erupts, it cools and solidifies
  • It’s magnetic materials points towards earth’s magnetic North/South, recording the evidence of earth’s polarity at that time
• Evidence to support plate tectonic theory

  Zebra-like pattern is symmetrical on either side of mid-ocean ridges, showing that it is not random/isolated occurrence
• Evidence to support plate tectonic theory

  • Oceanic plate move away from each other
  • Iron-rich lava erupts from the centre of the ridge
  • Lava cools, solidifies, and form new oceanic crust
  • Crust is pushed from both directions away from the ridge when new lava erupts and solidifies as plates move apart
  • When earth’s polarity reverses, the rocks record the reversals
  • Overtime, as more lava moves away from the ridge due to plate divergence, a symmetrical zebra-like pattern forms