The Mid-Atlantic Ridge

By Amy GarrisonG355May, 2009

The platePlate Tectonics - quick review:The theory that the Earths surface is broken into a number of thick plates that are slowly and continuously movingThis 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 Earths 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 sea-floor spreading:Ocean floor magnetism and magnetic reversalsDid you know that about every half million, years the Earths magnetic polarity reverses ??So does the magnetization of the ocean floor.

Magnetic ReversalsMolten lava emerges from volcanoSolidifies to a rock ~ usually (black) basaltBasalt 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 ridgeSimilar magnetic strips were also observed in all other oceans.

Lab

Information credits:http://www.google.com/search?hl=en&defl=en&q=define:plate+tectonics&ei=cb4QSsqgIKL6tQPV17znCw&sa=X&oi=glossary_definition&ct=titlehttp://en.wikipedia.org/wiki/Mid-Atlantic_Ridgehttp://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=/images%3Fq%3Dimage%2B%2Bof%2B%2BAlfred%2BWegener&hl=en&usg=__5izJRZ-nvCQrrYYUvrcw4lpYf0g=&ei=t8AQSsTPBYOKtAO3ibj3Ag&sa=X&oi=image_result&resnum=4&ct=image

Photo credits:http://whc.unesco.org/en/activities/504/http://www.iki.rssi.ru/mirrors/stern/earthmag/Figures/wegener.gifhttp://en.wikipedia.org/wiki/Mid-Atlantic_Ridgehttp://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_definition&ct=titlehttp://www.mysciencebox.org/seafloorhttp://www.google.com/imgres?imgurl=http://www.a3bs.com/imagelibrary/U19550/electricity-and-magnetism/U19550_pair-of-bar-magnets-80-mm.jpg&imgrefurl=http://www.a3bs.com/shop/u.s.a./electricity-and-magnetism/magnetism,pg_83_671_623_0.html&h=438&w=400&sz=26&tbnid=5_erY2DpNAoZdM::&tbnh=127&tbnw=116&prev=/images%3Fq%3Dimages%2Bof%2Bmagnets&hl=en&usg=__KVEICqH0EQSLrBnBhyUfANR44v8=&ei=IuQRSueBJI78swOn2MjyDQ&sa=X&oi=image_result&resnum=4&ct=imagehttp://www.google.com/imgres?imgurl=http://www.platetectonics.com/oceanfloors/images/Africa-South_America_4.jpg&imgrefurl=http://www.platetectonics.com/oceanfloors/africa.asp&h=260&w=245&sz=17&tbnid=2nSSaPr8WOzrDM::&tbnh=112&tbnw=106&prev=/images%3Fq%3Dimages%http://www.windows.ucar.edu/teacher_resources/magnetism/mid_atlantic_ridge_10_inch.jpg

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