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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: So und N avigation A nd R anging - PowerPoint PPT Presentation
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The Ocean FloorThe Ocean Floor
I. New TechnologyI. New Technology
New technology = new information.
New information = new ideas & theories
http://www.audiblox2000.com/images/brain_scratching_head.gif
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 TechnologyI. New Technology
http://www.lowrance.com/images/Tutorials/Sonar/sonar2.gif
I. New TechnologyI. New Technology
II. Ocean Floor Topography
It was assumed the ocean floor was flat.
It wasn’t: huge underwater mountain ridges and valleys
Mid-Ocean Ridgesunderwater mountains that are thousands of
miles long.
Located in the center of the oceans
Volcanoes and earthquakes are very common along the ridges.
II. Ocean Floor Topography
http://www.log.furg.br/WEBens/ocean/wormuth/marineprovinces/natlanticseafloor.gif
Deep-Sea Trencheshuge underwater valleys up to 7 miles deep.
Found along the edges of many oceans.
Earthquakes are very common near deep-sea trenches.
II. Ocean Floor Topography
III. The Oceanic Crust
Scientists took samples of rocks from the ocean floor.
Age of the oceanic crustCloser to mid-ocean ridges = younger.
Further from a ridge the older the rocks.
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
III. The Oceanic Crust
IV. Another New Technology
Magnetometer- measures small changes in magnetic fields.
First used in the oceans during the 1950’s.
A new type of self-propelled 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 self-propelled magnetometer.
http://oceanexplorer.noaa.gov/explorations/02fire/background/rovs_auvs/abe_220.jpg
V. The Earth’s Magnetic Field
paleomagnetismthe study of Earth’s magnetic field throughout
history.
Magnetic ReversalsEvery 10,000 years or so:
The north & south magnetic poles switch places.
http://anthro.palomar.edu/time/images/magnetic_north_pole.gif
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
V. The Earth’s Magnetic Field
Image from: http://www.indiana.edu/~geol116/week7/magstrip.jpg
A-Ha!
New crust is created at oceanic ridges!
V. The Earth’s Magnetic Field
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.
Crust pulls apart
Magma rises up and fills the gap left when the crust pulled apart
The magma hardens, creating new oceanic crust
VI. Seafloor Spreading
Eureka!!Eureka!!Seafloor spreading explains HOW the
continents move.
Solves one problem people originally brought up about Alfred Wegener’s theory of continental drift!
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