How is sea floor spreading different from continental drift?
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Sea floor spreading is the driving force behind continental drift as it forces the crust apart.  The hot mantle rises to the surface weakening the crust until it splits and moves apart to allow the new material to form.  This rifting creates new oceanic basaltic crust rather than granitic continental crust so the continents stay roughly the same. \n\nHowever, rifting does occur within continents and eventually will split a continent, as is happening in the Red Sea today, the East African Rift being a failed offshoot of that rift system.\n\nAll this happens slowly at a rate of about 11cm a centuary and if you want to see an active spreading ridge take a trip to Iceland where the Mid Atlantic ridge is on surface.  Don't worry it is perfectly safe and you won't end up on the wrong side.
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Some are moving away from each other (i.e. their separation is increasing), such as Africa and South America. Some are moving closer together, like North America and Asia. Some places continents or pieces of continents are moving past each other, like in the Pacific Northwest, or in the Afar Triangle in Somalia. Some places are expanding, like Iceland. \n\nThere are lots of ways to measure this, but the first clue that something was going on came from looking at the shapes of coastlines. Look at the coastlines of western Africa and eastern South America. They look like they could fit together, like a puzzle. The rocks match each other on both continents too, as if the two continents were once fit together. \n\nHowever, the big clue that something was going on came from magnetic stripes on the sea floor. As new basalt forms in the middle of the Atlantic, and some other oceans, it pushes out from the central mid-ocean ridge, and cools. When it cools, it sets, taking on a magnetization aligned with the magnetic field of the earth at that moment. However, the earth's magnetic field flips every few thousand years (just like the Sun's does, every 11.5 years or so). This creates a record of magnetic stripes on the sea floor that alternate polarity. When the scientists Vine and Mathews saw this, they knew they had proved that plate tectonics existed, and that the continents were moving (sometimes away from each other, and sometimes towards each other or past each other)
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Divergent Boundaries...\n\nContinental/Continental: rift valleys i.e. East African Rift Valley\n\nOceanic/Oceanic: new crust is being formed on the ocean floor at oceanic ridges. The Mid-Atlantic Ridge is an example. The U.S. moves about 5cm away from Europe each year b/c of this.\n\nConvergent Boundaries...\n\nContinental/Continental: Both are of the same density & both are less dense than the molten material beneath so neither will be subducted. They form folded mountain chains such as the Appalachians of the U.S. & the Alps of Europe.\n\nContinental/Oceanic: Ocean crust is much denser & will be subducted under the continental. Friction from plate movement underneath the crust will cause melt & the crust will thin causing some volcanic mountains to appear.\n\nOceanic/Oceanic: One of the oceanic crusts will be subducted & a trench will be created. Volcanic island arcs are associated w/ this type of boundary.
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The basic idea is that the earth's land mass was unified hundreds of millions of years ago, but has been gradually pulling apart since then.\nAnd large land masses are resting on huge plates. The plates bump against each other, and when one of them shifts,\nyou have an earthquake.\nThink of it like a jigsaw puzzle, but with continent-sized pieces.\n\nFor lots of pictures of plates, and faults, visit here:\nhttp://www.seismo.unr.edu/ftp/pub/louie/class/100/plate-tectonics.html
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It becomes rock on the surface of the ocean floor. It is eventually carried further & further away.\n\nSome older rock created by this process has already been "recycled" in the rock cycle; it became molten when it was subducted under continental plates.\n\nAn interesting fact is that as new rock is being created at the Mid Atlantic Ridge, the earth's magnetic field is being recorded right into the rocks. Any time there is a change in the direction of the earth's magnetic field it has been recorded.\n\n:)
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This is the Wilson Cycle, and it is driven by plate tectonics. \n\nContinents are composed of relatively light weight felsic igneous rocks such as granites and granodiorites. Ocean basins are composed of mafic igneous rocks like basalt and gabbro that are heavier than continental crust. Since the earth's mantle is plastic, these different masses of rock tend to 'float' at different levels. This is called isostacy.\n\nOceanic plate motion originates at the mid-ocean ridges, pushing oceanic plates outward towards the continents. This motion and force is far from being uniform from one ocean basin to another, and is not even consistent along the length of the mid-ocean spreading centers. \n\nWhere oceanic plates meet continental plates there is a convergent plate boundary and generally this leads to subduction of the oceanic plate. There is considerable force however, and the style of subduction does vary. Since the forces that are being applied, as well as the resistance of the continental plates all are varied, there are inequities that cause the continents to move in one direction. Eventually this motion results in a collision of continents called a supercontinent because continents will not subduct under one another. India and Asia, and the Himalayas are a great example of a continental convergent plate boundary. Eventually the convection forces that cause the supercontinent to form will begin rifting it apart again creating new smaller continents. \n\nHere is a model of the Wilson Cycle:\nhttp://csmres.jmu.edu/geollab/vageol/vahist/wilsonsimp.html
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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.
133507
The magnetic striping of the seafloor is similiar on both sides of an oceanic rift.  They match up like puzzle pieces.
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It was once thought that land on earth is stationary and that the continents had always been their current shape, even though they may have been covered by more water.\n\nMore recently however, it has been discovered that the continents were actually all one mass of land and at one point separated, floating apart on sheets of plate tectonics.  \n\nProof came quickly.  It is now easy to see the east coast of South America fitting into west Africa for instance.  Bones of related land-dwelling creatures were also found on the coastlines of the two distant continents.
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Oceanic crust is generally thinner since it is closer to the mantle, more dense since it is composed of mainly mafic basaltic rocks (have more ferromagnesians in them, i.e. iron) , and younger than continental crust since it is in a constant state of change near subduction zones and gets reformed sooner and more often then continental crust.
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According to Wicipedia, Oceanic trenches are typically 3 to 4 kilometers deeper than the surrounding sea floor. The average overall depth of the ocean is 4 kilometers. And the Deepest part of the the ocean is the Marianas Trench in the Pacific which reaches depths of 11,000 meters.  \n\nAccording to SJWamback, Ocean trenches such as the Marianas Trench are the places where giant slabs of ocean floor actually sink back toward the mantle of the earth and melt. These trenches and subduction zones are a portion of the process of Plate Tectonics which moves Earth's continents and sea floors and recycles the entire crust of the Earth throughout its history.   Deep Eh?   \n\nSuzi from Buffalo
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Magma, or molten rock located beneath the earth's surface, cools upon reaching the surface to form the crust. This crust is moved away from the location of upwelling by thermal convection currents in the semi-plastic mantle. The crust is then resorbed back into the mantle upon meeting another, less dense (more buoyant) crust. \n\nThere are two types of crust: oceanic and continental. Each are made from different minerals, resulting in oceanic crust being 'heavier' (denser) and thus sinking below the 'lighter' (less dense) continental crust at convergent boundaries. The earth's crust is in a state of constant motion (or, in some places, no motion, but a building up of energy) called plate tectonics. \n\nSee the wikipedia link below for more details. Hope that helped.
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Well believe it or not it is the composition of the two. \ncontinental crust is "typically" silicic, meaning it is composed largely of silica rich minerals, oceanic crust is more commonly "mafic" meaning it is composed of minerals with abundant Iron and Magnesium.  This oceanic crust is heavier.\nBecause of this the continental crusts are "floating" higher than the oceanic crusts.  When the two converge (i.e. along the west coast of south america for example) typically the lower oceanic crust is subducted beneath the continental crust..\nCool huh
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These are all related to the crusts. \n\nA divergent boundary occurs when two Earth tectonic plates move away from each other, causing a depression or a range. \n\nSubduction occurs underwater when seawater tectonic plates converge into continental plates. Since seawater tectonic plates are more dense than continental plates, it 'subduct's and goes under. \n\nThere's more than 3 types of magma, depending on its temperature, density, and composition.\n\nAs you know, the plate tectonics theory says that the Earth's crust is moving constantly. By applying the observations of divergent boundaries through time (ex, Great Rift Valley created over centuries), that will -support- and -clarify- the plate tectonics theory. So, divergent boundaries being observed serves as evidence and support for the theory.\n\nSubduction occurs in sea-floor spreading, which explains why crusts closer to the mid-atlantic ridge are "warmer" and "younger", while the ones further away, and most likely closer to a subduction zone is colder. This shows that the Earth's crust is once again moving, once again indicating that the theory is true. \n\nMagma is formed when divergent boundaries move away from each other, and is replaced by new crusts formed by magma. The cycle of sea-floor spreading undergoing subduction, sinking under the continental crust, melting into magma, then re-forming  at the Mid-Atlantic ridge.
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The reponse is related to plate tectonics. The earth crust is composed of a larger number of plates that float, very slowly of course, over the liquid interior. Continents therefore move relative to each other. When two plates meet, generally one moves under the other and it is here that we find mountains and volcanoes.\n\nWhat relation with oceans? Well, between some of the plates there is an upwelling of new magma, new crust. This is for instance the case in the middle of the Atlantic Ocean. The new crust needs room and pushes the plates on the left and right away: the Americas are moving to the west, while Europe and Africa are moving to the east. \n\nOceans (ah, at last!) are watermasses in which such upwelling of fresh crust takes place. An ocean therefore is partly in two or more different plates. On the other hand, seas are bodies of water that are on one continental plate only, or on two plates were no new crust is formed.\n\nHere is a pictures of the different continental plates:\n http://en.wikipedia.org/wiki/Image:Plates_tect2_en.svg
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your question is a little confused , but here goes...\n\nthe lithospere is the name for the outer/upper layer of the earths surface. It has 2 compositional layers, the CRUST, the upper solid layer, and the MANTLE, the lower molten layer. They are separated by the MOHO DISCONTINUITY. the moho discontinuity diffracts earthquake waves, which is why it is believed that the mantle is composed of molten rocks (other waves, such as sound and light waves are diffracted when crossing the boundary between a solid/liquid or liquid /gas, so it is believed there is a change of state at the moho). The Moho occurs at a depth of about 200-300 km beneath the earths surface.\n\nMost plates do have oceanic and continental lithosphere, the difference is only that oceanic is under the sea, and continental is on land, if you consider that the deepest ocean, and the highest mountain are both roughly 3 miles deep/high, and the lithosphere is about 300 miles deep , you will see that defining  a plate as oceanic or continental has little impact on its overall composition or behaviour.\n\nIn short the crust is the upper, the mantle is the lower , the moho is the boundary\n\n\n**\n\nin answer to bertrum ( see below) the North Sea is hardly an ocean, continents usually have a 'continental shelf' around them, which is considered geologically to be part of the continent, and beyond which the true ocean starts, the North Sea covers  part of the continental shelf of the European Plate
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Continent is a geographical term and not a geological term (plate-tectonic).\n\nMajor geographical boundries of lands separating one from the other form a continent and thus a continent is a big peace of land separated through geographical differenciation from others.