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NAME: __________________________________________ CLASS PERIOD: 2 3 4 5 6 SEA FLOOR SPREADING Sea-floor ____________ is a process that continually adds new material to the ocean floor. It is the process by which new oceanic lithosphere forms as magma rises toward the surface and solidifies. Spreading Process 1. Starts at the __________________ 2. Molten material rises from the _____________ and erupts. 3. The molten material then ____________________ 4. Pushes ___________ rock to both sides of the ridge. 5. The molten material ___________ 6. Forms a strip of solid rock in the center of the ridge. 7. More molten material splits apart the strip of solid rock. 8. _______________ it aside. 9. The process starts over again. Evidence of Sea Floor Spreading 1. Magnetic _____________: Throughout Earth’s history, the north and south magnetic poles have changed places many times. When the poles change places, the __________ of Earth’s magnetic poles changes ____________ rock at mid-ocean ridges contains tiny mineral grains of ________. These minerals align with Earth’s magnetic field. When molten rock cools, the minerals solidify in place and record information about the polarity of the Earth during a certain period of time. If the magnetic field changes, the grains will align in the ___________ direction. 2. Mid-Ocean Ridge: The longest chain of ______________ in the world Discovered using a __________ which is a device that bounces sound waves off underwater objects, and then records the echoes of these sound waves. Curves along the sea floor, extending into _______ of the Earth’s oceans. If seafloor spreading DID NOT occur, the ocean floor would be ___________. NAME: __________________________________________ CLASS PERIOD: 2 3 4 5 6 3. Rocks shaped like ________ that can only form if molten material hardens quickly after erupting under water have been found in the central valley of the mid-ocean ridge. 4. Scientists took samples of rocks for testing. Rocks ________ away from the ridge were older than the ones __________ to the ridge. If seafloor spreading DID NOT occur, all of the oceanic crust would be the __________________ _______________. Does the ocean floor just continue to get bigger and bigger? NO! The ocean floor sinks beneath deep underwater canyons called deep-ocean ___________________ Where there are trenches, _______________________ takes place. Subduction is the process by which the ocean floor _______________________beneath a deep-ocean trench and back into the mantle. Fun Facts These processes cause the ocean floor to be renewed about every ____________________ years. The __________________________ Ocean is shrinking – the trenches are swallowing more ocean crust than the mid-ocean ridge is producing. The _______________________ Ocean is expanding – in most places the oceanic crust is attached to the continental crust. Which two boundary types balance each other? A _______________________ boundary, which ________________ new crust, and a ___________________ boundary, which ___________________crust.