Download Sea Floor Spreading

Sea Floor Spreading
Chapter 9.4
https://www.youtube.com/watch?v=GyMLlL
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Wegener could not explain how the
continents moved but . . .
• Harry Hess could!
• He called his idea
Sea Floor Spreading
After World War II:
• Scientists began to experiment with new
tools.
• One that measures Sound Waves
Echo - Sounding
• Sound waves were
sent to the bottom of
the ocean floor.
• The longer it took
the deeper the water.
Because of this Scientists Discovered:
• Underwater Mountains, Volcanoes & Valleys
Mid-Atlantic Ridge
• The World’s Largest Mountain Range
• And it is UNDERWATER!
Mid-Atlantic Ridge in Iceland???
(Pingvellir, Iceland)
Iceland is on different plates that
are moving away from each other
(diverging)
This is happening all over the Ridge . . .
How it works
• Magma is forced upward & the sea floor
spreads apart.
• Magma cools & sinks as it flows away forming
a high ridge.
• The magma then turns to solid crust forming
new ocean floor.
Proof of Sea Floor Spreading
• Rock samples were taken:
– Youngest rock near the ridge
– Oldest rock was found towards the shore.
More Proof – Magnetic Clues
• -Magnetite is magnetic.
• -Magnetic minerals are attracted to Earth’s
magnetic field.
• When magma containing these minerals cools,
it freezes the magnetic mineral grains
• so they point in the direction of the Earth’s
magnetic field.
Over time, Earth’s
magnetic field
changes (reverses
direction).
-As a result, the
direction the minerals
point changes with it.
Paleomagnetism
• These changes result in magnetic striping along
the ocean floor.
• Each beige and red stripe indicates a change in
Earth’s Magnetic field.