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The Ocean Floor I. New Technology New technology = new information. New information = new ideas & theories http://www.audiblox2000.com/images/brain_scratching_head.gif I. New Technology Echo-Sounding: SoNAR: Sound Navigation And Ranging Became common on warships during World War II Used by scientists to make maps of the ocean floor. I. New Technology http://www.lowrance.com/images/Tutorials/Sonar/sonar2.gif II. Ocean Floor Topography It was assumed the ocean floor was flat. It wasn’t: huge underwater mountain ridges and valleys II. Ocean Floor Topography Mid-Ocean Ridges underwater mountains that are thousands of miles long. Located in the center of the oceans Volcanoes and earthquakes are very common along the ridges. http://www.log.furg.br/WEBens/ocean/wormuth/marineprovinces/natlanticseafloor.gif II. Ocean Floor Topography Deep-Sea Trenches huge underwater valleys up to 7 miles deep. Found along the edges of many oceans. Earthquakes are very common near deep-sea trenches. III. The Oceanic Crust Scientists took samples of rocks from the ocean floor. Age of the oceanic crust Closer to mid-ocean ridges = younger. Further from a ridge the older the rocks. III. The Oceanic Crust Age of the oceanic crust vs. age of continental crust Oldest Oceanic Rocks: 180 million years old Oldest Continental Rocks: 3,800 million years old IV. Another New Technology Magnetometer- measures small changes in magnetic fields. First used in the oceans during the 1950’s. A new type of selfpropelled magnetometer. http://oceanexplorer.noaa.gov/explorations/02fire/background/rovs_auvs/abe_220.jpg IV. Another New Technology Magnetometers measured the magnetic field of the ocean floor. A new type of selfpropelled magnetometer. http://oceanexplorer.noaa.gov/explorations/02fire/background/rovs_auvs/abe_220.jpg V. The Earth’s Magnetic Field paleomagnetism the study of Earth’s magnetic field throughout history. Magnetic Reversals Every 10,000 years or so: The north & south magnetic poles switch places. http://anthro.palomar.edu/time/images/magnetic_north_pole.gif V. The Earth’s Magnetic Field What the magnetometers found: Symmetric magnetic stripes around ridges! The stripes had normal and reversed magnetic fields. Each stripe was formed when the magnetic pole shifted. V. The Earth’s Magnetic Field Image from: http://www.indiana.edu/~geol116/week7/magstrip.jpg V. The Earth’s Magnetic Field A-Ha! New crust is created at oceanic ridges! VI. Seafloor Spreading Harry Hess (1906 – 1969) He proposed the theory of seafloor spreading. Seafloor Spreading New crust is being created at the mid-ocean ridges. Old crust is destroyed at the oceanic trenches. VI. Seafloor Spreading Crust pulls apart Magma rises up and fills the gap left when the crust pulled apart The magma hardens, creating new oceanic crust Eureka!! Seafloor spreading explains HOW the continents move. Solves one problem people originally brought up about Alfred Wegener’s theory of continental drift!