cycle/process of seafloor spreading?
112608
Thats the theory of lithospheric evolution that holds that the ocean floors are spreading outward from vast underwater ridges. \nFirst proposed in the early 1960s by the American geologist Harry H. Hess, its major tenets gave great support to the theory of continental drift and provided a conceptual base for the development of plate tectonics.\n\nBUT...\n\nAlfred Wegner came up with continental drift! \n\nA geological theory that the relative positions of the continents on the earth's surface have changed considerably through geologic time. Though first proposed by American geologist Frank Bursley Taylor in a lecture in 1908, the first DETAILED theory of continental drift was put forth by German meteorologist and geophysicist Alfred Wegener in 1912.
603115
volcanos\ntectonic plates movements
123973
Giant rock plates pushing against each other suddenly slip causing the earth to move, sending out ripples like in a pond.\n\nChildren can recreate the action of a fault slipping with their hands.  Place both hands together, palm-to-palm.  Push the palms together.  While pushing the palms together, slide one hand forward away from the body while sliding the other hand back toward the body.  At first, nothing will happen.  As force is added to the forward-backward movement, the hands will suddenly slip, much as the earth does during an earthquake.
797755
It happens in the brittle part of the crust, which is not usually deeper than 20 km.\n\nHere's the jist:\n\nIt all comes down to stress and strain. It is not 'the plates rubbing together' as many people say; or at least that's a very simplistic view.\n\nPlate tectonics causes stress on the continents and oceans, all over the surface of the earth. In some places, the stress is very small (usually within the plates). Elsewhere, the stress is high, usually where the plates meet each other. Since each plate moves, when two come in contact, the stress each other. They can push on each other and cause compressional stress, they can pull with extensional stress, and they can slide past or shear each other with tensional stress.\n\nFaulting, causing earthquakes, comes from the fact that this stress is building up all the time, but rocks and continents are strong materials. Just like hitting a rock with a small hammer, you do put stress on it, but a small amount. It would take a sledgehammer to put enough strain (effects and accumulation of stress) to build up and cause breakage. In the earth, the area around an active fault builds up strain from the stress of plate tectonics. Most faults become locked, because of this strength, and thus can not release their strain. Away from the fault, the stress produces very small and slow movement of the rock masses as a whole. Eventually, the strain is too much and the rest of the plate has moved too far and the fault releases the strain build-up all at once in a big stress release called an earthquake. This is called the elastic rebound theory, and it explains most (but not all) movements.\n\nThis is why an earthquake's size is relative to the fault size. The bigger the fault, the bigger the strain build up, and the bigger the release in an earthquake. Subduction zones and collision zones, where large portions of plates actually can rub together as a whole, have the really big earthquakes, like the 2004 Sumatra earthquake. In other plate boundaries, the entire plate boundary does not act together, so the faults become spread out and many faults take up the strain from the tectonic stress, like with the San Andreas Fault in California (it only takes up ~3/4 of the stress between the plates).\n\nEarthquakes are really tricky things; there is still so much we need to learn. As of now, there is no way to predict them, but we can say where the danger is highest and about how long between events.
108402
Oceanic crust is formed by volcanism at the mid-ocean ridges, also called spreading centers. Magma upwells from within the asthenosphere or mantle. It often does not erupt onto the sea floor but rises through complex cracks and fissures where it encounters cooler rock and sea water. Other areas actively erupt and lava flows in sheets typically less than 10 meters thick. For example, at the Juan de Fuca Ridge, the process creates about 6 meters of new crust in 100 years. Oceanic crust consists of basalt, often referred to as MORB (mid-ocean ridge basalt).
24692
The best answer from the above choices: \nSlow moving convection currents within the molten aesthenosphere supply new material to the spreading centers in the earth's ocean floors and other places. These currents are thought to provide force to cause the motion of the oceanic plates, either directly, or indirectly through the mid ocean ridge building process. \n\nSubduction is only one part of the process of plate tectonics, that does provide some driving force by pulling the subducting plate downward. \n\nGravity has a role as well, as without gravity, the mid-ocean ridges would not have the weight to provide force with which to push the plates apart at the spreading centers, and the subducting plates would not have the force to pull plates. \n\nThe earth's magnetic field may have the least to do with plate tectonics, possibly no role at all.
964505
The earth's hard surface (commonly called the crust) can be composed of oceanic crust or continental crust.  The two types of crust can form to create plates.  (Refer to plate tectonic theory)\n\nThe creation of the earth's crust can be a result of many processes such as: volcanism (Hawaii/Mt.St. Helens), Rift Zones (Mid-Atlantic Spreading Center), or combinations of the two.\n\nThe boundaries of these plates can convergent (come together), divergent (move apart), or transverse one another (slide past one another). \n\nOne of the most famous boundary between plates is the transverse or strike/slip fault that commonly creates earthquakes in California. The two famous faults are the San Andreas and Hayward faults.  \n\nEarthquakes are simply a build up of forces on these plate boundaries and eventually break.  The "break" is the earthquake  that we feel, the aftershocks can continue after the initial break, but are usually less intense or less strong (see Richter Scale)\n\nTsunamis are the result of deep earthquakes on/or near the ocean floor.  The movement of the fault will move massive amounts of the oceans water table is shifted. This forms a wave that will generate out in all directions.  When the tsunami travels thousands of miles thru the ocean and comes into contact with land it produces large scale waves (anywhere from 20-300+ feet) in height.
967662
It all comes down to stress and strain. It is not 'the plates rubbing together' as many people say; or at least that's a very simplistic view.\n\nPlate tectonics causes stress on the continents and oceans, all over the surface of the earth. In some places, the stress is very small (usually within the plates). Elsewhere, the stress is high, usually where the plates meet each other. Since each plate moves, when two come in contact, the stress each other. They can push on each other and cause compressional stress, they can pull with extensional stress, and they can slide past or shear each other with tensional stress.\n\nFaulting, causing earthquakes, comes from the fact that this stress is building up all the time, but rocks and continents are strong materials. Just like hitting a rock with a small hammer, you do put stress on it, but a small amount. It would take a sledgehammer to put enough strain (effects and accumulation of stress) to build up and cause breakage. In the earth, the area around an active fault builds up strain from the stress of plate tectonics. Most faults become locked, because of this strength, and thus can not release their strain. Away from the fault, the stress produces very small and slow movement of the rock masses as a whole. Eventually, the strain is too much and the rest of the plate has moved too far and the fault releases the strain build-up all at once in a big stress release called an earthquake. This is called the elastic rebound theory, and it explains most (but not all) movements.\n\nThis is why an earthquake's size is relative to the fault size. The bigger the fault, the bigger the strain build up, and the bigger the release in an earthquake. Subduction zones and collision zones, where large portions of plates actually can rub together as a whole, have the really big earthquakes, like the 2004 Sumatra earthquake. In other plate boundaries, the entire plate boundary does not act together, so the faults become spread out and many faults take up the strain from the tectonic stress, like with the San Andreas Fault in California (it only takes up ~3/4 of the stress between the plates).\n\nEarthquakes are really tricky things; there is still so much we need to learn. As of now, there is no way to predict them, but we can say where the danger is highest and about how long between events.
640247
The plates consist of an outer layer of the Earth, the lithosphere, which is cool enough to behave as a more or less rigid shell. Occasionally the hot asthenosphere of the Earth finds a weak place in the lithosphere to rise buoyantly as a plume, or hotspot. \n\nOnly lithosphere has the strength and the brittle behavior to fracture in an earthquake. \n\nThe map below locates earthquakes around the globe. They are not evenly distributed; the boundaries between the plates grind against each other, producing most earthquakes. So the lines of earthquakes help define the plates: \n\n\nIn cross section, the Earth releases its internal heat by convecting, or boiling much like a pot of pudding on the stove. Hot asthenospheric mantle rises to the surface and spreads laterally, transporting oceans and continents as on a slow conveyor belt. The speed of this motion is a few centimeters per year, about as fast as your fingernails grow. The new lithosphere, created at the ocean spreading centers, cools as it ages and eventually becomes dense enough to sink back into the mantle. The subducted crust releases water to form volcanic island chains above, and after a few hundred million years will be heated and recycled back to the spreading centers.
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The rock cycle is the continuous movement of rock from one type to another. These processes occur over long amounts of time. All rock started out as igneous. From there, rock can then become sedimentary, metamorphic, or igneous again in any order.\n\nIgneous --> Sedimentary:\nIgneous rocks break down through weathering processes. The broken down rock becomes sediments which are deposited by wind or water. Layers of sediment build up on top of each other. Pressure, along with dissolved minerals, help to "glue" the rock together.\n\nSedimentary --> Metamorphic ("change form"):\nIf the pressure is great & enough heat is applied, metamorphism can occur. This causes the rock to become more compact & dense. If too much heat is applied then the rock will melt. See below.\n\nMetamorphic --> Igneous:\nIf heat is applied to the point of melting, the rock will go though the igneous phase again.\n\n:)
281207
A spreading center. The mid-Atlantic Ridge is the most well known example of a spreading center.\n\n*Edit*\nConvergent boundaries (subduction zones) have accretion wedges, and so are also accreting plate boundaries.
1124898
It is a complex process, so I will try to hit on the most important factors. \n\nIn past years oil exploration was done based on the observation of oil seeps at the surface. In many areas oil seeps out of the ground naturally, so these were likely places to drill. As geologic understanding grew, geologists realized that certain structures were likely to contain oil. The first geologist going into Saudi Arabia identified drilling sites from the deck of the ship before he even landed. He could see the structures that were likely to contain oil. As the easy finds have been drilled, the process has gotten much more scientifically rigorous. \n\nOften oil exploration starts with an exercise called basin modeling. Geologists look at ancient basins and use available evidence to determine \n1) if there is adequate source rock of sufficient organic content and of the proper organic content to generate oil\n2) if the burial and subsidence history of the basin was such that at some time in the past the source rock was forced to a depth where the temperature and pressure were ideal for petroleum generation \n3) the oil expelled from the source rock had a migration path that allowed it to escape from the source rock\n4) there were traps created by structure (anticlines, synclines, fault blocks, etc) or stratigraphy (variations in rock composition) that existed at the same time as the migration took place \n5) there was a seal on the trap that prevented escape of the oil or gas over the long period of time that the oil resided there\n6) the past heat gradient of the basin was such that the temperature of the source rock reached the ideal temperature range and did not get too hot or stay too cold. \n\nAs you can guess, a good understanding of a basin's geologic history is necessary, including it's deposition, burial, subsidence, uplift, and faulting history. Misunderstanding or incomplete evidence of any one of these factors results in more risk of failure. \n\nThe efficiency of the kitchen (the area where the organic material in the source rock is being 'cooked' into oil) can be evaluated with several different kinds of data. Certain organic compounds known as vitrinite can be examined and can give visual evidence of the maximum temperature they have reached. These samples are taken from well cuttings so the approximate depth of the sample is known. Bottom hole temperatures of existing wells are commonly measured and plotted on maps, as well as the temperature gradient coming up through the well. Apatite fission track analysis is another method for determining the thermal history of a sample and can tell the story of the burial history. \n\nIf there is adequate organic material of the proper makeup and if it can be predicted that it reached a temperature of more than 140 degrees F, then it was likely to generate oil. While it was between 140 F and 320 F it would have been generating oil, and beyond about 200 F, it would have started generating natural gas. If it stayed in the high end of that range long enough, the oil would have changed to natural gas. Beyond about 390 F both oil and natural gas will break down and change to graphite. Understanding this thermal history will lead to predictions about the existence and the potential quantity of oil and gas in a basin. \n\nPressure is also a factor in this process. When the hydrostatic or lithostatic pressure reaches a certain point, oil will begin cracking to form natural gas. Quite often this change can generate what is called overpressure in the reservoir, where the reservoir pressure actually is higher than lithostatic pressure and it can be dangerous for drilling if not anticipated.\n\nOne of the most fascinating parts of this basin modeling process is that different oil reservoirs can be identified by a geochemical signature that can be traced back to the original source rock. Often when working in a basin there is more than one source rock, and more than one possible mig
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G: The rock cycle.  See source.
809527
I think its called 'subduction', where one tectonic plate goes under another. It occurs at 'subduction zones', such as on the west coast of the United States. The reason it occurs is that one plate is expanding and the edges need to go somewhere (under another plate). For example, the Atlantic plate is expanding from the center because there is a north-to-south line of underwater volcanoes, spewing out magma and forcing the 2 halves of the plate apart to the west and east.
8512
Magnetic striping on the sea floor was used as an early proof of plate tectonics, as it showed the sea floor was spreading away from a central axis.\n\nThe following is taken from http://volcano.und.nodak.edu/vwdocs/vwlessons/plate_tectonics/part9.html\n\nIn the late 1950's, scientists mapped the present-day magnetic field generated by rocks on the floor of the Pacific Ocean. The volcanic rocks which make up the sea floor have magnetization because, as they cool, magnetic minerals within the rock align to the Earth's magnetic field. The intensity of the magnetic field they measured was very different from the intensity they had calculated. Thus, the scientists detected magnetic anomalies, or differences in the magnetic field from place to place. They found positive and negative magnetic anomalies. Positive magnetic anomalies are places where the magnetic field is stronger than expected. Positive magnetic anomalies are induced when the rock cools and solidifies with the Earth's north magnetic pole in the northern geographic hemisphere. The Earth's magnetic field is enhanced by the magnetic field of the rock. Negative magnetic anomalies are magnetic anomalies that are weaker than expected. Negative magnetic anomalies are induced when the rock cools and solidifies with the Earth's north magnetic pole in the southern geographic hemisphere. The resultant magnetic field is less than expected because the Earth's magnetic field is reduced by the magnetic field of the rock.\n\n     When mapped, the anomalies produce a zebra-striped pattern of parallel positive and negative bands. The pattern was centered along, and symmetrical to, the mid-ocean ridge.\n\n    A hypothesis was presented in 1963 by Fred Vine and Drummond Matthews to explain this pattern. They proposed that lava erupted at different times along the rift at the crest of the mid-ocean ridges preserved different magnetic anomalies.\n\nVine and Matthews proposed that lava erupted on the sea floor on both sides of the rift, solidified, and moved away before more lava was erupted. If the Earth's magnetic field had reversed (changed from one geographic pole to the other) between the two eruptions, the lava flows would preserve a set of parallel bands with different magnetic properties. The ability of Vine and Matthews' hypothesis to explain the observed pattern of ocean floor magnetic anomalies provided strong support for sea floor spreading.
839321
The mechanisms of tectonic plate movement is quite complex, but in its simplest terms, tectonic plates float on molten magma of the earth's interior. Convection currents within the molten magma behave similarly to convection currents in a pan of water being heated on the stove. Water on the bottom of the pan is heated and begins to rise because it is slightly less dense than the cooler water on the top. The cooler is slightly more dense and begins to sink. As this water is heated, it begins to rise, thus a convection movement or convection current is created in the water in the pan. \n\nMagma is far more dense than water and is much hotter, but it is still a fluid. Magma near the core is hotter than the magma beneath the crust. Hotter magma moves up, cooler magma moves down, very very very slowly, but none the less, it moves. The crust, a.k.a. tectonic plates float on the magma. Float some pieces of Styrofoam on the water in the pan. What happens? The foam moves around by the convection forces in the water.  Tectonic plates do the same thing. Its just not as fast.\n\nHope this helps.
1102973
Not at all. \n\nThe most convincing evidence that led to the acceptance of plate tectonic theory are stripes of magnetized rock that are arranged parallel the mid-ocean ridges and continue all the way to the edges of the ocean basins. These stripes grow progressively older in age as they approach the edges of the oceans, and correspond to past reversals of the earth's magnetic field. Each stripe formed during a period of Earth's history while the magnetic field orientation was steady, and as the field reversed, a new stripe with opposite orientation was formed. Here is a diagram that represents this:\nhttp://www.ucmp.berkeley.edu/geology/tecmech.html\n\nOther types of evidence that changed the paradigm from the old continental drift to plate tectonics was the discovery of mid-ocean ridges, which are volcanic chains larger than the Himalayas that stretch along the center parts of each ocean basin. These are active volcanic zones that are constantly forming new oceanic crust. \n\nPlate tectonics is an especially well proven and robust concept. Evidence of past plate movement is found in all parts of geology, from deposits of oil in both Africa and Brazil that came from the same source, to widespread rocks deposits on different continents that match in composition and character. Biological evidence in the form of fossils adds to the story, and plate tectonics is an important complement to the Theory of Evolution because it explains why some related organisms have had the opportunity to evolve differently in isolation. \n\nAs mentioned, the relatively new science of geodesy, prompted by satellite technology, can now measure the movement of continents precisely, and also can measure the changes in elevation of mountains as they rise. \n\nIf you would like to examine the changes in the earth's continental plates as a result of plate tectonics over time, here is a set of maps that show the movement of the earth's plates in the past and projected into the future:\nhttp://www.scotese.com/