Plate Tectonics

On Friday for the first part of class we took a quiz on the material we've been learning the past couple days and then we watched a movie! The movie started off with info about Alfred Wegener (Ms. Meyer said we should remember him for the test) who proposed the theory of continental drift in the early 1900's which became the basis for the modern day theory of plate tectonics. Wegener discovered that the our modern continents used to fit together into a super continent that he called pangea. In the 1950's oceanographers began using sonar to discover the layout of the ocean crust. With the sonar they discovered that the ocean floor was very rugged and covered with ridges and trenches. The oceanographers discovered that volcanic and seismic (earthquake) activity outlined the continents, which helped support the theory of plate tectonics that says earth's crust is constantly moving. The lithosphere is made up of nine plates that are all outlined by ridges and trenches in the oceans. Where the plates meet is where volcanic and seismic activity is most prevalent. There are three types of plate boundaries, the first is a divergent boundary. A divergent boundary can be found in the ocean and on land where the plates are moving apart. Ocean trenches are created by this type of boundary. The second type of boundary is a convergent boundary. This is a zone where the plates are colliding. The result of this collision is the build up of mountains. The last type of boundary is a transformed plate boundaries. In this type the plates are neither seperating are colliding, but instead are just moving past eachother. This action results in build up stress which can create earthquakes. An example of a transformed boundary is the San Andreas fault in California. Happy Halloween everyone!