Sea Floor Spreading

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Sea Floor Spreading

• The Theory

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Sea Floor Spreading

• By 1969 geologists knew that the earth's crust
  moved.
• Evidence came from under-sea ridges.

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Evidence of Sea Floor Spreading

• 1. In rift valley, liquid lava
• erupts through cracks in
• thin crust.
• 2. Lava solidifies into new
• sea-floor rock on both
• sides of the ridge.

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Evidence of Sea Floor Spreading

• 3. The rate of spreading is
• 1 to 10 cm/year.
• 4. Age of rocks increases
• equally on both sides as
• distance from rift
• increases.

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Evidence of Sea Floor Spreading

• 5. Oldest sea-floor rocks are
• only 1/10 as old as oldest
• land rocks.
• 6. Sediments get deeper as
• distance increases.

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Evidence of Sea Floor Spreading

• 7. Temperature decreases
• with distance.
• 8. Magnetized iron in rocks
• shows equal bands on both
• sides of rift of reversed
• polarity. (Polar Wandering)

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Magnetic Polar Wanderings

• Today the north pole is the magnetic south pole!

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Evidence of Magnetic Polar Wanderings

• 1. Bands of rocks containing
• magnetized iron that show
• reversed polarity.

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Evidence of Magnetic Polar Wanderings

• 2. The position of the "north"
• pole has moved from the
• Pacific ocean to its
• present location.

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Difference in Sea floor Spreadingand Continental
Drift

• 1. The theory of C.D. says that
• continents move slowly
• along the earth's surface.

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Difference in Sea floor Spreadingand Continental
Drift

• 2. S.F. spreading and
• magnetic polar wanderings
• tell how C.D. works.

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Difference in Sea floor Spreadingand Continental
Drift

• 3. Plate tectonics adds that
• these continents have
• moved because they are
• passengers on rigid plates
• of rocks that move on the
• surface of the earth