Transcript The Ocean Floor

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!