Sea-Floor Spreading

1
Sea-Floor Spreading

• Chapter 9, Section 4
• The Mid-Ocean Ridge
• Longest mountain chain in the world
• It is almost entirely under water, but some areas
  do peak out of the ocean.
• Example Iceland

2
Sea-Floor Spreading

• As new rock emerges from the rift valley, older
  rock is pushed towards the edge of the ocean.
• http//www.wwnorton.com/college/geo/egeo/animation
  s/ch2.htm

3
Evidence for S.F.S.

• Molten Material
• Pictures of molten material rising from the
  mid-ocean ridge have been taken.
• The molten material cools very quickly due to the
  contact with cold ocean water.
• http//www.wwnorton.com/college/geo/egeo/animation
  s/ch2.htm

4
Evidence for S.F.S.

• Magnetic Stripes in the ocean floor
• Earths magnetic poles (caused by the inner core
  spinning) have reversed themselves in the past.
• If they reverse again, our compasses will point
  south. http//www.wwnorton.com/college/geo/egeo/an
  imations/ch2.htm

5
Evidence for S.F.S.

• Drilling Samples
• Scientist drilled the sea-floor to get rock
  samples.
• The older rocks were found far from the mid-ocean
  ridge.
• The younger rocks were found near the mid-ocean
  ridge.

6
Subduction at Deep-Ocean Trenches

• Subduction means to sink below.
• This allows the ocean floor to sink back into the
  mantlea recycling of sorts.
• http//www.wwnorton.com/college/geo/egeo/animation
  s/ch2.htm

7
Subduction and Earths Oceans

• The Pacific Ocean is SHRINKING!!!
• More oceanic crust is subducted than is being
  produced, because there are more trenches.
• The Atlantic Ocean is GROWING!!!
• More oceanic crust is being produced than
  subducted because there are fewer trenches.