Main features of plate tectonics are:
- The Earth's surface is covered by a series of crustal plates.
- The ocean floors are continually moving, spreading from the center, sinking at the edges, and being regenerated.
- Convection currents beneath the plates move the crustal plates in different directions.
- The source of heat driving the convection currents is radio activity deep in the Earth's mantle.
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Where plates crash together are called convergent boundaries. The plates only move a few centimeters each year so collisions are slow and can last millions of years. This crash has caused a huge mountain to form at the continental plate and the oceanic plate has pushed deeper into the Earth. A water trench has formed at it's base. All the folding and bending makes rock in both plates break and slip causing earthquakes. Some of the rock at the base of the continental plate melts and rises up through it and erupts as a volcano.
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Where the plates of the crust are coming apart are called divergent boundaries. When the Earth's surface pulls apart, it usually comes apart in parallel faults and tilts outward. When the plates separate, the block that form in the middle usually drops into the soft asthenosphere. Its forms a valley called a rift. Magma then seeps up and fills the cracks forming a new crust. Earthquakes occur along the faults and volcanoes form where the magma comes to the surface. An example of a divergent boundary that crosses land is the Rio Grande Rift in New Mexico. An example of one that crosses over the ocean is the Mid-Atlantic ridge.
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Transform boundaries are caused when plates slide past each other. Since there is no tearing of the crust when they pass each other, they aren't as impressive as divergent or convergent boundaries. These kind of formation are found where a stream bed have split in half and the two halves have moved in opposite directions. The most famous boundary of this type is the San Andreas Fault. California that is to the west of the fault is moving north. These sliding motions cause lots of earthquakes and there have been many along the San Andreas fault.
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John Tuzo Wilson was a Canadian geophysicist. Wilson knew Harry Hess when he was a young lecturer back in the 1930's. He developed a concept crucial to the plate tectonics theory. He thought the Hawaiian and other volcanic island chains formed due to movement of a plate over a stationary hot spot in the mantle of the Earth. Another of Wilson's important contributions to the development of the plate tectonics theory was that there must be a third type of plate boundary to connect the oceanic ridges and trenches that can end abruptly and and transform into major faults that slip horizontally. A well known example of this type of fault is the San Andreas Fault Zone. Since they transform the Earth's crust horizontally, they don't change or destroy it.
Continental Drift to Plate Tectonics
How did that happen?
How did that happen?
Scientists as early as 1596 thought that the continents drifted apart. They believed that they were torn away by earthquakes and floods. Alfred Wegener studied many aspects of the continental drift theory. He gathered information from different authors and studies and put it all together . He would make speeches on his theory . January 6, 1912 he gave a speech to the German Geological Society. He told of the "puzzle like fit" of the continents; of the fossils plants and animals were found on different continents then what they could have survived on; also mountain ranges that have similar rock formations that fit together on opposite shores. His ideas weren't taken seriously. Wegener wasn't the first to suggest Continental drift but was the first to present evidence from several fields.
After technology advancement and the suggestion of continental drift, geologists would look to try and prove if the theories were true. With the development of advance technology, looking at rock formations in the ocean and being able to take samples of the ages of rock, they were able to find that the earth's land was a moving object. They were able to find out about Seafloor Spreading. They were also able to study glacial marks. Scientific theories could take years and maybe even decades to get acceptance among scientists. Being able to study how the continents move, to how the seafloor recreates itself, and to understand how earthquakes happen provide crutial information today that prove scientific the plate tectonics theory.
After technology advancement and the suggestion of continental drift, geologists would look to try and prove if the theories were true. With the development of advance technology, looking at rock formations in the ocean and being able to take samples of the ages of rock, they were able to find that the earth's land was a moving object. They were able to find out about Seafloor Spreading. They were also able to study glacial marks. Scientific theories could take years and maybe even decades to get acceptance among scientists. Being able to study how the continents move, to how the seafloor recreates itself, and to understand how earthquakes happen provide crutial information today that prove scientific the plate tectonics theory.