Continental drift
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Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.Seafloor spreading helps explain continental drift in the theory of plate tectonics. 
http://www.mlhi.org/science/period6/Sea.htm We didn’t know exactly what the ocean floor looked like until the development of sonar. Define sonar and explain how it was used to map the ocean floor. Sonar, which stands for SOund Navigation And Ranging, works by measuring the time it takes for sound to travel to a reflecting surface and back. Check out the following webpage for an explanation of how it works. http://earthguide.ucsd.edu/earthguide/diagrams/sonar/sonar.html Sonar revealed a 40,000 mile long chain of underwater mountain ranges called mid-ocean ridges. Name three of the longer mid-ocean ridges found around the world (see http://images-mediawiki-sites.thefullwiki.org/09/1/2/9/15028053949789413.gif). Mid-Atlantic, Central Indian, and Pacific Antarctic (any others could work here, too) There are several pieces of evidence that sea floor spreading is occurring. One piece of evidence is the age of the ocean crust (see http://geology.about.com/od/platetectonicmaps/ss/World-Seafloor-Ages.htm). Describe where the youngest ocean crust is found and explain why it is found there. The youngest crust is found at the mid-ocean ridges (generally in the middle of the ocean basins). This is where magma is rising through rifts, or cracks, in Earth’s crust. When the magma cools it forms new sea floor rock. What type of igneous rock forms when magma cools at mid-ocean ridges? Basalt Another piece of evidence for sea floor spreading is found in the magnetic record of the rocks on the ocean floor. The sea floor rocks show alternating bands of normal and reverse polarity with a mirror image of the pattern on the other side of the mid-ocean ridge (see http://www.pbs.org/saf/1207/features/Platetech6.htm). This pattern could only be generated if spreading was occurring at the mid-ocean ridge. Define normal and reverse polarity. Normal polarity: Time when the compass needle points to the magnetic north pole. Reversed polarity: Time when a magnetic needle points to the south pole. http://www.ge-at.iastate.edu/glossary-of-geologic-terms/ A third piece of evidence for sea floor spreading is how the thickness of ocean sediment changes as you move away from the mid-ocean ridge. What happens to the thickness of ocean sediment as you move away from a mid-ocean ridge and explain why this is the case? The thickness of the ocean sediment increases as you move away from the mid-ocean ridge because the rock is getting older and the sediment has been settling for a longer time the farther away from the ridge you are. In addition to mid-ocean ridges, sonar also revealed many ocean trenches around the world. These trenches, or deep depressions, are the deepest parts of the ocean basins and are formed at subduction zones. Define subduction zone and explain why it occurs. A subduction zone is where a denser tectonic plate goes under another, less dense, tectonic plate. This occurs at a convergent boundary. 
http://www.geo.cornell.edu/hawaii/220/PRI/images/subduction2.jpg Continental drift and sea floor spreading eventually gained enough evidence and support to become theories. These theories led to the theory of plate tectonics. Define the theory of plate tectonics. Plate tectonics is the theory that Earth's outer shell is divided into several plates that glide over the mantle, the rocky inner layer above the core. The plates act like a hard and rigid shell compared to Earth's mantle. This strong outer layer is called the lithosphere. 
http://www.livescience.com/37706-what-is-plate-tectonics.html There are between 15 to 20 tectonic plates. These plates move in different directions and different speeds on the Earth’s surface. The tectonic plates are made up of lithosphere. Define lithosphere. Directory: cms -> lib01 -> VA01000173 -> Centricity -> Domain lib01 -> At the Old Haunted House By: Helen Ketteman Illustrated: Nate Wragg Synopsis Domain -> You Gotta Know These Programming Languages C++ lib01 -> Howard High School / Information Technology 2014-2015 course syllabus program concentration lib01 -> NS3-M1U1C1 The Importance of Sea Power (Exam) Domain -> Course Guide Domain -> Locate the seven continents and the five Oceans Continents (a) Download 0.82 Mb. Share with your friends:
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