Lothear Wegener was the first person to theorize the idea of plate tectonics. The theory of plate tectonics is a combination of the ideas that explain the continental drift and the spreading of the sea floor. Plate tectonics became a well accepted theory by geologists. Although Wegener had suggested that the continental plates plowed through the ocean floor, actually the continents and the ocean floor from the plates float on the underlying rock called asthenosphere.
In 1911, Wegener was looking through some scientific papers in the library in Marlburg Bermany University Library. One of the papers listed several fossils that were identical and found on opposite sides of the Atlantic Ocean. In one of his books he wrote, "A conviction of the fundamental soundness of the idea took root in my mind." Wegener began to notice the undeniable evidence before him like the puzzle-like fit of the South American and Africa Coastlines. He also discovered that some fossils found in other places indicated that an extremely different climate from the climate found today. Some other facts he collected and presented in his book, The Origin of Continents and Oceans are:
In the early Paleozoic, Gondwanaland was considered a supercontinent. It was located in the South Pacific and stretched possibly from the equator to the South Pole.
Laurentia was located on the opposite side of the globe. It later became North America. To the east Baltica, which is now a major part of Europe was located.
The Acadian and Taconic Orogenies
Around 500 million years ago, Larurentia and Baltica crashed into one another. During the lower Ordovicean period, the Southern most islands of Baltica collided with what is now New York state. This event caused theTaconic Orogeny which formed the Taconic mountains west of the Hudson River.
The Acadian Orogeny
The Acadian Orogeny occurred continually through out the Devonian and Mississipian. As Laurentia and Baltica crashed together, the ocean between them was obliterated. This orogeny fomed a mountain range that extended through Nova Scotia and to Greenland. In the mean time Gondwanaland was moving across the South Pole.
The Appalachian Orogeny
Gondwanaland was moving North, Laurentia and Baltica combined and became known as Laurussia. The three continents began to combine . During this time another smaller continent collided with Baltica's eastern margins. This act uplifted the Ural mountains. It is believed that the land masses were joined by the Permian period and lasted for most of the Mesozoic era.
The following is a picture of Pangea 135 million years ago. The continents
are separating and moving away from one another.
The Grenville Orogeny occured when an oceanic plate was subducted beneath the North Amercan plate which halted the drifting of the continent. There was little tectonic activity in the Grenville supercontinent. This caused the underlying sediment to rebound and become dome-shaped. Around 660 million years ago, the notheastern U.S. became covered by a shallow sea maned the Iapetus Ocean. Due to the crumbling of the Grenville supercontinent, 110 million years later an arc of volcanic islands formed off the coast of Ancient North America. These islands are considered to be Japan in the modern day. The islands also caused the next mountain-building event, the Taconic Orogeny.
In the beginning there was a cloud of material that slowly condensed into a central ball. This is the Sun. It contained a spinning plate of material. That material clumped together into the planets that swept up the flying material. The heavier peices gravitated towards the inner regions and the lighter to the outer regions. There is a distance from the sun that is too unstable for inknown reasons to support a planet, so that the original material only clumps up to a certain extent before breaking up once again.
Planets, as they attract material, get larger and larger, producing more and more gravity which exerts pressure on the inner regions which lead to the liquefaction of the material there.
Up to this time, the planet doesn't rotate and therefore, as is the case with the moon, exposes one side constantly to the sun. This is because the atoms making up the core are randonly placed. As liquefaction occurs, they are able tomove and line themselves up. When that happens all atoms rotate similarly and momentum begins to build up producing rotation of the earth.
Before complete liquefaction the sun's attraction produces a bulge on the side of teh earth facing it. When water begins to condense and to fill up the oceans produce the land mass. As complete liquefaction occures, the land mass finds itself to be floating on the liquid and begins to drift, but it encounters forces that limit free movement, most likely those would evelove from currents under the crust. These currents produce cracks in the crust through which the magma is allowed to flow. This produces counter forces to those which propel Pangea, resulting in the breakup of Pangea and the current statis of the continents.
http://home.earthlink.net/~dlblanc/tectonic/pangea.html
http://www.ucmp.berkeley.edu/history/wegener.html
http://volcano.und.nodak.edu/vwdocs/vwlessons/plate_tectonics/introduction.html
http://www.whfreeman.com/college/Earth Science/textbooks/tectonics
http://mydl.soe.umich.edu/mygeology/theory.html
http://earthview.sdsu.edu/trees/tecqest.html
This web page was created by:
Belinda Bailey, Stephanie Chambers and Angie Rogers