7th grade ch. 1 sec. 4 sea-floor spreading
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Ch. 1 Sec. 4
Sea-Floor Spreading
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mid-ocean ridgemid-ocean ridge• winds beneath Earth’s oceans
• mapped using sonar= device that bounces sound waves off underwater objects & records echoes
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The mid-ocean ridge (shown in red) winds its way between
the continents much like the seam on a baseball.
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Harry Hess’ idea-
Ocean floors move like conveyor belts- carrying continents with them
Movement begins at mid-ocean ridge
Molten material rises from mantle & erupts
Molten material spreads out- pushing older rock to both sides of the ridge
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sea-floor spreadingsea-floor spreading
• new material continually being added to ocean floor
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evidence for
sea-floor spreading
1.molten
material
2.magnetic
stripes
3.drilling samples
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1. Evidence from molten material
The submersible Alvin photographed pillow lava along the mid-ocean ridge.
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2. Evidence from magnetic
stripes
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• The Glomar Challenger was the first research vessel specifically designed in the late 1960s for the purpose of drilling into and taking core samples from the deep ocean floor.
3. Evidence from drilling samples3. Evidence from drilling samples
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deep-ocean trenchdeep-ocean trench
• deep, underwater canyon
• forms where oceanic crust bends
• subduction takes place here
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subductionsubduction• process where oceanic crust sinks down
beneath trench into mantle
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Because of sea-floor spreading, the
distance between Europe and North
America is increasing by a few
centimeters per year.
Growing an Ocean
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Ocean crust is returned to the mantle
through subduction
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1. oceanic lithosphere is created @ mid ocean ridge
2. moves across ocean basin for 175 mill. yrs.
3. returns to mantle in Earth's subduction zones
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mid-ocean ridgemid-ocean ridge
• winds beneath Earth’s oceans
• mapped using sonar= device that bounces sound waves off underwater objects & records echoes
![Page 23: 7th grade Ch. 1 Sec. 4 Sea-Floor Spreading](https://reader033.vdocuments.site/reader033/viewer/2022051514/54925aa6b479591d2c8b4891/html5/thumbnails/23.jpg)
sea-floor spreadingsea-floor spreading
• theory proposed by Harry Hess
• new material is continually being added to ocean floor
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deep-ocean trenchdeep-ocean trench
• deep, underwater canyon
• forms where oceanic crust bends
• subduction takes place here
![Page 25: 7th grade Ch. 1 Sec. 4 Sea-Floor Spreading](https://reader033.vdocuments.site/reader033/viewer/2022051514/54925aa6b479591d2c8b4891/html5/thumbnails/25.jpg)
Evidence for sea-floor spreading
1. molten material2. magnetic
stripes3. drilling samples
![Page 26: 7th grade Ch. 1 Sec. 4 Sea-Floor Spreading](https://reader033.vdocuments.site/reader033/viewer/2022051514/54925aa6b479591d2c8b4891/html5/thumbnails/26.jpg)
subductionsubduction• process by which oceanic crust sinks down beneath trench mantle
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Harry Hess
What scientist helped to discover the process of sea-
floor spreading?
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mid-ocean ridges
Along what feature of the ocean floor does sea-floor
spreading begin?
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Evidence from
The submersible Alvin photographed pillow lava along the mid-ocean ridge.
molten material
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• The Glomar Challenger was the first research vessel specifically designed in the late 1960s for the purpose of drilling into and taking core samples from the deep ocean floor.
Evidence fromEvidence from drilling samplesdrilling samples
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Evidence from
magnetic stripes