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Sea Floor Spreading

Sea Floor Spreading. Unit 1, Section 3 Bill Nye the Science Guy: Sea Floor Spreading. - Sea-Floor Spreading. Mid-Ocean Ridges. Mid-Ocean Ridge – ocean water sinks through cracks in crust (vents).

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Sea Floor Spreading

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  1. Sea Floor Spreading Unit 1, Section 3 Bill Nye the Science Guy: Sea Floor Spreading

  2. - Sea-Floor Spreading Mid-Ocean Ridges • Mid-Ocean Ridge – ocean water sinks through cracks in crust (vents). • The water is heated by contact with hot material from the mantle, then spurts back into the ocean

  3. Mapping the Mid-Ocean Ridge • Mid-Ocean Ridge is the longest chain of mountains in the world • Ocean floor is mapped using sonar • Sonar – a device that bounces sound waves off underwater objects than records the echoes of the sound waves • The time it takes for the echo to arrive indicates the distance of the object

  4. Mapping the Mid-Ocean Ridge

  5. Sequencing Sea Floor Spreading Molten material rises from the mantle and erupts Molten material then spreads out, pushing older rock to both sides of the ridge As the material cools, it forms a strip of solid rock in the center Then, more molten material flows into the cracks The material splits apart and the solid rock is pushed aside

  6. - Sea-Floor Spreading What Is Sea-Floor Spreading? • Sea-Floor Spreading – process of continually adding new materials to the ocean floor • The sea floor spreads apart along both sides of the mid-ocean ridge as new crust is added • As a result, the ocean floor moves like a conveyor belt, carrying the continents along with it.

  7. - Sea-Floor Spreading Growing an Ocean • Because of sea-floor spreading, the distance between Europe and North America is increasing by a few centimeters per year.

  8. - Sea-Floor Spreading Evidence for Sea-Floor Spreading • Several types of evidence supported the theory of sea-floor spreading: • Eruptions of molten material • Magnetic strips in the rock of the ocean floor • Ages of the rocks themselves.

  9. Evidence from Molten Material • New material is erupting along the mid-oceanic ridge • A deep-sea diving crew found strange rocks shaped like pillows • Pillow shaped rocks can only form when molten material hardens quickly after erupting underwater • Presence of these rocks showed that molten material is continually erupting from cracks in the sea floor

  10. Pillow Lava • Underwater Pillow Lava • Starts at 1:12 • Underwater Volcano

  11. Evidence from Magnetic Strips • Earth behaves like a giant magnet • Earth’s magnetic poles have reversed themselves • Ocean floor lies in a pattern of magnetized strips • The strips hold a record of reversals in Earth’s magnetic field

  12. Earth’s Magnetic Field

  13. How can we tell the magnetic field have reversed? • Rock contains iron • As molten material cools, iron bits inside line up in the direction of the Earth’s poles • When rock hardens, the iron parts remain in place and act like a ‘ magnetic memory’ • This is just like setting a bunch of tiny compasses in cement

  14. Evidence from Drilling Samples • Samples have been taken from the sea floor by drilling • Scientist can determine the age of rocks in samples • Further away from ridge = Older rock • Closer to ridge = Younger rock

  15. Question • If new crust is continually being made at the Mid-Ocean ridge, why does the size of the Earth not increase?

  16. - Sea-Floor Spreading Subduction at Trenches • Deep-Ocean Trenches – ocean floor plunges into deep underwater canyons • A deep-ocean trench forms where the ocean floor sinks back into the mantle through the deep-ocean trenches.

  17. Sequencing Subduction Convection Currents under the lithosphere pushes new crust that forms at the Mid-Ocean Ridge, away from the ridge and towards the deep ocean trench New crusts is very hot but cools and become denser when it leaves the mantle Gravity pulls the older, denser oceanic crust down beneath the trench

  18. Subduction and Sea-floor Spreading • Subduction– process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle • Subduction and sea floor spreading can change the size and shape of the ocean • Ocean floor is renewed about every 200 years!

  19. Subduction Pacific Ocean Atlantic Ocean • Old & Shrinking • Deep-Ocean Trench is destroying more crust than the Mid-Ocean Ridge can produced • Destroyed > Produced • New & Growing • Has only a few trenches to destroy crust • More crust is being produced than can be destroyed • Destroyed < Produced • The ocean floor is attached to the continental crust, resulting in the movement of the continents

  20. Identify the feature at each #

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