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The Mid-Atlantic Ridge
By Amy Garrison
G355
May, 2009
The plate
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Plate Tectonics - quick review:
The theory that the Earth’s surface is broken into a number of thick plates
that are slowly and continuously moving
This contributes to Continental Drift
The plate tectonics theory was first proposed by Alfred
Wegener, a German meteorologist, in 1912
~ It is the concept that the Earth’s crust is composed of
rigid plates that move over a less rigid interior.
There are 3 different kinds of boundaries where
2 plates come together: Divergent – which is
what the mid-atlantic ridge is, Convergent and
Transform.
A divergent boundary is where two different plates
are moving in opposite directions - away from each
other. New crust is created as the old crust
moves away, similar to a conveyor belt.
• In the case of the mid-Atlantic ridge, a mountain range was
formed from this process.
• It is located along the floor of the Atlantic Ocean and is the
longest mountain range in the world.
• It separates the Eurasian Plate from the North American Plate
in the North Atlantic, and the African Plate from the South
American Plate in the South Atlantic.
• It extends from a junction with the Mid-Arctic Ridge, northeast of
Greenland southward, to the Bouvet Triple Junction in the South
Atlantic.
• These plates are still moving
apart, so the Atlantic is growing
at the ridge at a rate of about
2.5cm per year, in an east-west
direction.
• While the Mid-Atlantic Ridge is mostly an
underwater feature, there are portions of it
that have enough elevation to extend above
sea level.
• Some of the islands that have been created
and are part of this ridge are
Iceland, the Azores,
Bermuda, and Saint
Peter and Paul Rocks.
A fissure running along the Mid-Atlantic
Ridge in Iceland
• An important discovery that has to do with seafloor spreading:
• Ocean floor magnetism and magnetic reversals
• Did you know that about every half million, years
the Earth’s magnetic polarity reverses ??
• So does the magnetization of the ocean floor.
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Magnetic Reversals
Molten lava emerges from volcano
Solidifies to a rock ~ usually (black) basalt
Basalt is faintly magnetic, like iron.
Its magnetization is in the direction of the local
magnetic force at the time when it cools down.
• Instruments can measure the magnetization of
basalt.
• Suggested that times existed when the magnetization had the
opposite direction from today's.
• In the end it was determined that in the distant past, the
magnetic polarity of the Earth was sometimes reversed.
• Magnetization in the ocean was orderly, arranged in long
strips.
• Strips on the Atlantic ocean floor, in particular, all seemed
parallel to the "mid-Atlantic ridge."
• Not only were the magnetic strips lined-up with the central
ridge,
• Their structure and distribution seemed remarkably
symmetric on both sides
• As "plates" on each side are pulled away,
• Lava emerges from the middle, solidifies and "records" the
prevailing magnetic field.
• The newly formed basalt sticks to the plates and is also pulled
away
• Every half million years, on the average, the Earth's magnetic
polarity reverses, and so does the magnetization of the ocean
floor.
• Each strip represents an epoch of one or the other magnetic
polarity, and the symmetry is also explained.
• The sea-floor is a giant tape recorder, with twin tapes
emerging from the mid-Atlantic ridge
• Similar magnetic strips were also observed in all other
oceans.
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Lab
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Information credits:
http://www.google.com/search?hl=en&defl=en&q=define:plate+tectonics&ei=cb4QSsqgIKL6tQPV17znCw&sa=X&oi=glossary_definitio
n&ct=title
http://en.wikipedia.org/wiki/Mid-Atlantic_Ridge
http://www.google.com/imgres?imgurl=http://www.iki.rssi.ru/mirrors/stern/earthmag/Figures/wegener.gif&imgrefurl=http://www.iki
.rssi.ru/mirrors/stern/earthmag/reversal.htm&h=304&w=216&sz=29&tbnid=eWzDjXMBhF5MvM::&tbnh=116&tbnw=82&prev=/image
s%3Fq%3Dimage%2B%2Bof%2B%2BAlfred%2BWegener&hl=en&usg=__5izJRZnvCQrrYYUvrcw4lpYf0g=&ei=t8AQSsTPBYOKtAO3ibj3Ag&sa=X&oi=image_result&resnum=4&ct=image
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Photo credits:
http://whc.unesco.org/en/activities/504/
http://www.iki.rssi.ru/mirrors/stern/earthmag/Figures/wegener.gif
http://en.wikipedia.org/wiki/Mid-Atlantic_Ridge
http://www.epm.geophys.ethz.ch/~cfinlay/Images/core_cut.jpg
http://www.nature.nps.gov/geology/usgsnps/pltec/vigil595x266lab.jpg
http://www.google.com/search?hl=en&defl=en&q=define:plate+tectonics&ei=cb4QSsqgIKL6tQPV17znCw&sa=X&oi=glossary_definitio
n&ct=title
http://www.mysciencebox.org/seafloor
http://www.google.com/imgres?imgurl=http://www.a3bs.com/imagelibrary/U19550/electricity-and-magnetism/U19550_pair-of-barmagnets-80-mm.jpg&imgrefurl=http://www.a3bs.com/shop/u.s.a./electricity-andmagnetism/magnetism,pg_83_671_623_0.html&h=438&w=400&sz=26&tbnid=5_erY2DpNAoZdM::&tbnh=127&tbnw=116&prev=/ima
ges%3Fq%3Dimages%2Bof%2Bmagnets&hl=en&usg=__KVEICqH0EQSLrBnBhyUfANR44v8=&ei=IuQRSueBJI78swOn2MjyDQ&sa=X&oi=i
mage_result&resnum=4&ct=image
http://www.google.com/imgres?imgurl=http://www.platetectonics.com/oceanfloors/images/AfricaSouth_America_4.jpg&imgrefurl=http://www.platetectonics.com/oceanfloors/africa.asp&h=260&w=245&sz=17&tbnid=2nSSaPr8WOzr
DM::&tbnh=112&tbnw=106&prev=/images%3Fq%3Dimages%
http://www.windows.ucar.edu/teacher_resources/magnetism/mid_atlantic_ridge_10_inch.jpg