seafloor spreading theory

• Sea floor spreading theory

  New crust is being created at mid-ocean ridges, destroyed at deep-sea trenches
• Harold Hess


  • 1906-1969
  • Professor of geology at Princeton Uni, USA
  • Became interested in geology of oceans while serving as US Navy in WWII
  • Proposed theory in 1962
• Sonar or echo sounding


  Used to map North Pacific Ocean floor
• Magma


  • Hotter and less dense is then forced up to the ocean floor, cooling off when touches water
  • When hardens, a new ocean floor is added to Earth's crust
• Sea floor spreading


  Magma rises and cools then pushes the new sea floor away from the ridge
• Mid ocean ridge


  • Or ocean mountain ranges
  • Seafloor mountain system formed by plate tectonic
  • Where seafloor spreading takes place along a divergent (away) plate boundary

  
• Plate boundaries


  • Subduction - Oceanic and continental lithosphere is recycled into Earth's mantle and convergent (collide) boundaries
  • Ocean trenches - Long, narrow depressions on the seafloor, deepest parts of the ocean created by subduction

  
• Molten materials


  • Rock pillows or pillow-shaped rocks
  • Indicates that molten material erupted repeatedly from mid-ocean ridge cracks and cooled quickly
• Magnetic stripes


  • Ocean floor rock patterns of magnetizing stripes record reversals in Earth's magnetic field
  • Shifting of north and south poles
• Drilling samples


  • Older rocks are found away from the ridge
  • Youngest rocks are found in the heart of the ridge
• Tectonic plates theory


  • Unifying theory of geology
  • Plates move relative to each other by sliding on top of the non-solid asthenosphere
  • Plates are earth's lithosphere (solid outer shell) broken into big, rigid pieces
  • Explains earth's surface movement, current and past, that created mountain ranges and deep oceans