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!