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Seafloor Spreading

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by

Adrienne Ash

on 9 April 2014

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Transcript of Seafloor Spreading

How do the continents move?
Sediment Thickness
Scientists found very little sediment on the ocean floor. The thinnest (least) sediment was found around the mid-ocean ridges, and the thickest sediment was found near the edges of some continents.
Ocean Floor Mapping
Scientists used sonar to map the ocean floor, and discovered a series of mid-ocean ridges all around the world.
Seafloor Spreading
The process by which new crust is added to the ocean floor at the mid-ocean ridges.

http://earthguide.ucsd.edu/eoc/teachers/t_tectonics/p_seafloorspreading.html
Magnetometry Data
The data scientists found when taking magnetometry readings of the ocean floor showed a pattern of stripes that alternated between normal (pointing north) and reversed (pointing south) magnetic polarity.
Age of the Oceanic Lithosphere
By using radiometric dating to determine the age of core samples taken from the ocean crust, scientists were able to determine that the oceanic lithosphere is youngest on the mid-ocean ridges, and gets older as you move away from the ridges. They also found that the oldest ocean rock is only about 200 million years old, as opposed to the oldest continental rock, which is about 4 billion years old.
Harry Hess
The geologist who put all of the data together and developed the idea of seafloor spreading, which answered the question Alfred Wegener could not - how do the continents move?
A rock from a banded iron formation in northern Quebec, Canada. This sample measures a few inches across. At 3.75 billion years of age, it is one of the oldest rocks on Earth. "These rocks, with meteorites, are the only time travel machines into the early history of our planet," said University of Chicago geoscientist Nicolas Dauphas. (Credit: Photo by Dan Dry)
Radiometric Dating
http://www.pbs.org/wgbh/evolution/library/03/3/quicktime/l_033_01.html
http://www.pbs.org/wgbh/nova/earth/when-our-magnetic-field-flips.html
Magnetic Pole Reversals
Mid-Atlantic Ridge
Alfred Wegener:
not so crazy after all!

Core Samples
Oldest Continental Rock
Harry Hess published his idea in a report called "History of Ocean Basins".
http://scilib.ucsd.edu/sio/hist_oceanogr/hess-history-of-ocean-basins.pdf
Full transcript