Explain how magnectic bands provide evidence that tectonic plates are moving apart at mid-oceanic ridges.
133893
When liquid magma comes out of the earths crust at the mid-oceanic ridge, it cools rapidly forming crystals. These crystals have magnetic properties that align the crystal according to the earths magnetic field at the time they cooled, similar to how a compass needle points north, the magnetism in the crystal indicates which direction was north when the crystal was formed.\n\nHowever, the direction that is north today, was not always north in the past, in fact many times in geologic history, the north and south poles were reversed entirely. This is reflected in the "magnetic bands" found in rock on the ocean floor.\n\nSo, if you imagine the Atlantic Ocean between the U.S. and Europe, there is a mid-ocean ridge between the two. If the plates never moved, then the magma coming out of this ridge would just pile up, but instead, this is the "engine" that moves the plates away from one another. As you move from the mid-ocean ridge towards the continents, the crystals in the rock have different magnetic orientations that show these flip-flops of the earths magnetic field through geologic history. Because this material originated at the mid ocean ridge, but is now closer to the continents, it shows that the earths crust, the floor of the ocean, is moving AWAY from the mid-ocean ridge and TOWARDS the continents.\n\nThere are a lot of  diagrams that would probably help you understand this better. CHeck out a geology book, or look online.\nGood Luck!
61755
Yes this is true. We know that this happens because of our recent observation but also because crystal formation in rocks shows us that in the past it has switched... Ya strange pockets of magnetic wierdness appear from time to time too(geologially speaking so like over 100,000 years) It all happens really slowly on human time scales but it can (in theory) happen pretty quick. Like over 100's of years. There are plenty of folks watching and taking note. Fortunately, those scientists in the know — paleomagnetists, to be exact — have a ready answer. There is even a really great computer model that they run to test all the variables and options... If it happend over night we'd be in trouble for sure... but it doesn't.
9132
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.
151885
One piece of evidence is the symmetry of ocean floor spreading.\n\nAnother is the way some of the continents seem to fit together like a jigsaw puzzle (the east coast of South America and the west coast of Africa, for example). \n\nYou could argue that the pattern of the Hawaiian volcanoes is evidence that the Pacific plate has travelled in a northeastenly direction over the hot spot now feeding the active volcanoes of Mauna Loa, Kilauea, and Loihi (underwater). The farther you move away from the hot spot in the southeast corner of the Hawaiian islands, the older and smaller the islands get, until you get to Kure Atoll and the seamounts beyond.
447714
A mid ocean ridge is an area where new sea floor is created throught the divergent (speading) motion of the tectonmic plates in that area. At mid ocean ridges, fractures from the pulling allow small amounts of magma to squeeze in and push the plates that much more.\n\nIt comes down to density. The center of the ridge is high, because it it new (just formed) and hot. The edges are low because it is old and cold. There are two main theories on the cause: slab pull and ridge push.\n\nRidge push is the classic idea that the ridge is a high point of a convection current, pushing the plates aside and allowing new mantle material to rise up and fill the hole.\n\nSlab pull is the new idea that the subducting end of the plate, that is really old and dense, pulls on the entire plate as it subducts, and thus pulls apart itself in places, causing a hole which is then filled by rising material, forming the ridge.\n\nIt's kinda a chicken/egg thing, so we may never be able to rule one or the other out.
185339
In geology it's typically subduction; two tectonic plates are colliding with one diving under the other.
418456
1. Continental drift or plate tectonics.\n\n2. Horizontal fault line.
414747
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.
181901
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
620650
the pac-o due to frequent movement of plates at the bottom of the ocean.
587740
Convection, driven by the release of heat from the Earth's mantle.   Like a pot of vegetable soup on the stove.   The vegetables on the surface move around.   Some are subducted and others surface.
329018
There are several lines which scientist use to prove that evolution is occurring which are embryology, palaeontology, evidence from similar anatomy\nIn case of Palaeontology this is the study of remains of past living organisms. In this case the remains are dug and they show a change from the top going down the earth's crust In this study at the top of the earth's crust the remains of organisms found are complex but going down deeper simple remains of organisms are found this suggest that organism are changing from simple form into complex forms.\nAnother thing that is observed are the remains of certain organism which don't exist by the time and remains of organisms which were not in the inner parts suggest that new species are formed
23149
Plate tectonics is the answer to your questions about weathering and erosion, as well as thickness of the continental crust. Plate tectonics moves and lifts continental plates continuously, and faster than erosion can carry the sediments away. Mt. Everest is a good example of this, as pressure from the adjoining crustal plates is lifting the mountain at a rate of a few centimeters a year. \n\nAs this pressure against the continental plates builds they often fold and break, and this causes parts of the contintal plates to slide up over other parts of the plate, making them thicker that the oceanic plates. \n\nAt present the only way to find the top of the mantle is using seismology. Siesmologists measure the way that shock waves (sound waves) move through the earth when earthquakes happen. By studying the way these sound waves are deflected from different rocks they can tell about how deep the boundary is between the crust and the mantle. \n\nHere is one of the best websites that explains plate tectonics. It has animated illustrations that show moving plates and how they have changed over time:\nhttp://www.ucmp.berkeley.edu/geology/tectonics.html
319592
The answer is definitely B.\n\nWegener used that along w/ the fact that certain rock types found in Africa also matched rocks in South America. Also he used the fact that the continents looked as though they fit together like a jigsaw puzzle.\n\nWhile Wegener proposed the hypothesis of continental drift he did not actually prove it.\n\nActually, it wasn't until the late 60's that the theory of plate tectonics actually proved Wegener's hypothesis & it became widely accepted.
5267
Tectonics (and therefore earthquakes and volcanoes) is driven by the internal heat of the planet.\n\nEver since the Earth formed it has been cooling, so if anything tectonic activity is on a constant decline. The loss of heat is very slow though, so from the point of view of recorded human history there has been very little change.
412084
The continental plates do not actually 'drift' as you may think of an ice cube 'drifting' in water. Nor are the plates all connected together like one would view a jigsaw puzzle.\n\nThe first idea you have to realize is that the continental plates overlap each other. The 'outlines' you see that appear jigsaw-like are more often than not areas where two plates meet, and one plate is actually going under  the one next to it- this is called 'subduction'.\n\nWhich plate goes under which plate depends on the age and weight of the plates-- continental crust is lighter than oceanic plate, so more often than not it is the oceanic piece of the plate that will 'subduct'.\n\nThere are areas, however, where the plates do actually meet like a jigsaw puzzle-- these places are known as "Strike-slip" faults, where two plates slide past each other rather than 'subducting'.\n\nAs for the plates moving, that happens due to the upper mantle (the liquid part under the crust) creating convective currents-- these 'currents of mantle material' cause the plates to move and subduct (or slide past each other!)\n\nAnd yes, there are plates where continental crust and continental crust meet. What happens then? More often than not, mountains form-- The Himalayas are a prime example of this situation (the Indian plate smashed into the Asian plate).\n\nThere's more to it, but I hope this helps a little bit!
117619
Man_with_a_Plan has no proof that there is no proof. His statement that no theories are sound or have proof is just his opinion and purely speculatory. There is no proof.\n\nI, on the other hand, like the "Murder on the Orient Express Theory". I think that there was huge changes in ocean circulation due to the continents coming together WELL BEFORE Pangaea formed. The geologic evidence suggests that the extinction happened in different places around the world at different times, which suggests that no single event is responsible. I believe that cooling events like plume volcanism in the Siberian traps coupled with warming events like methane hydrate release and greenhouse effect along with the continental positioning at the time may have worked together to cause extreme changes in ocean circulation at various parts of the world at different times, attributing to the extinction event.\n\nVariations in temperature due to greenhouse warming and on/off sulphide cooling would have had the greatest immediate impact on planktic (ocean surface) and shallow water organisms. I also think that ocean circulation was also greatly affected not only by the temperature variations but also the circumstantial orientation of the continents. Heat transport to the north would have been innefficient and consequently northern regions would have been subject to extreme cooling, even at relatively low latitudes. In the southern regions there would have been a huge temperature gradient between top and bottom waters. If this was enough to stop deep water formation and ocean turnover, benthic (bottom dwelling) species would have been destroyed by the lack of oxygen and intermediate to surface water species would have suffered from a lack of nutrients. Because most of the Earth's life at the time was in the water, I am quite sure that it was likely some change in ocean circulation that dealt the fatal blows to life. Obviously good carbon isotope data from the period would be needed to verify this hypothesis. \n\nLife on land would have suffered greatly by climate changes induced by changes in ocean circulation, as well as the extreme variations in temperature. Tropical species would have been devastated by cooling events caused by the plume volcanism.\n\nThere is lots of proof for everything; there just is no definite information that can, as of yet, say for sure exactly how it all happened. That's a tough thing to do, but I really dislike people who refute the claims of others without presenting any evidence themselves.