How does the magnetic alignment of sea floor spreading help to support the idea of sea floor spreading?
79414
It is very simple really, although my explanation may seem complex. This was first observed in the Pacific Ocean during World War 2.  The US Navy first noticed magnetic anomalies in the sea bed during anti-submarine operations that were using airborne magnetometers to detect submarines. They began to notice variations in the magnetic field of different areas. Oceanographers in the 1950's adapted this technology and began mapping the magnetic anomalies of the sea floor. What they found were that there were symmetric patterns of magnetic field reversals preserved in the rock of the seafloor that were in wide bands parallel to the mid-ocean ridges.  These reversals of magnetic field preserved in the seafloor correspond with reversals of the earth's magnetic field that have been taking place over time. These reversals can be dated using paleomagnetic measurements of rock samples combined with other geologic data such as fossil evidence and techniques such as potassium-argon dating. There is now a well established magnetic record of much of earth's history. These magnetic stripes along the seafloor provide excellent proof of sea floor spreading by showing that the oldest parts of the seafloor are along the ocean boundaries near subduction zones and intersections with continental plates.\n\nA very good explanation with illustrations and history is here: \nhttp://www.tectonic-forces.org/simplified.htm
920496
One theory of why a material, capable of being magnetised, becomes magnetic (i.e., attracts ferrous material), is that the individual, but randomly distributed 'domains' within are lined up (by some exterior force - e.g., magnetic field from a coil,  'stroking' with an already magnetised piece of iron/streel, etc.), so that the domains line up. The summation of their individual magnetic fields effectively produces one large magnetic field in  the material and makes what we call a magnet!   Some materials, after this process, retain their magnetism and are called permanent magnets, others, such as relay cores, once the external force is removed, exhibit very little residual magnetism.
698855
The directional North pole of the earth is a magnetic south pole, this is because the north end of a compass points north, and opposites attract, therefore north is...south.\n\nMagnetic lines go from south to north i think, sorry havn't taken electricity/mag class in so long...\n\nanyways, if my thining is correct than it would point towards the directional south\n\ni'd choose "down"
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.
156410
Yes, it is likely that we are experiencing a reversal at this time. \n\nThe earth's magnetic field has been decreasing in field strength by about 5% per century in recent times. This is one of the fastest decreases of the magnetic field that has ever been verified. Around 700 AD the earth's magnetic field was about 50% higher than it is now. At this rate, it is estimated that the earth could reach a zero-strength magnetic field in about 2000 years. Magnetic reversals are usually triggered when the field strength approaches zero.  Another indication that some geologists and geophysicists believe may be pointing to a reversal is that the poles have been wandering at a faster rate than is commonly seen in the rock record. This instability of the magnetic field suggests we may be close to a reversal. \n\nAlso consider that since we have never experienced a reversal this is hardly a certainty. The earth's magnetic field fluctuates quite widely during what are known as 'excursions', and these are as frequent as every 50,000 years. Our current changes in the magnetic field may result in nothing more than an excursion, which is not a reversal of the field. There have been at least 11 of these excursions since the last reversal at 730,000 years before present. \n\nI've done magnetostratigraphic work.
94737
Like a lot of things in science, it is hard to say exactly who first came up with this idea. \n\nHowever, probably the best contender is Professor Harry Hess of Princeton University. Hess noticed that the sediment near the mid-ocean ridges was much thinner, as though the sea floor there was newer than it was farther from the ridges. \n\nHowever, there are many others who played a part in solving this puzzle. Alfred Wegner, a German meterologist, is often credited with first proposing the theory of plate tectonics. Wegner noticed that the coastlines of South America and Africa fit together like pieces of a puzzle, but Francis Bacon, Benjamin Franklin, Antonio Snider-Pellegrini and others had noticed this before. Vine and Mathews observed the magnetic stripes on the sea floor, confirming Hess' theory.
363234
Well, it seems like someone hacked into AskJeeves, because I became so curious about your question that I went to AskJeeves. \n\nAnyway, visit this page:\n\nhttp://www.askforkids.com/web?q=Why+does+Earth+move+on+a+tilted+axis%3F\n\nPerhaps it shall work on your computer. Whenever I click on the result, it visits the page temporarily and then suddenly goes to a different page, which seems to want to advertise, though it's under construction.\n\nGreat question!\n\nI personally believe that if the Earth did not use a tilted axis, it would not have electromagnetic fields across it. This would vary the different compositions of materials, and though I do not have very much knowledge about this, it probably would mean that humans could not survive, because humans use electromagnetic forces for various things.
388039
In physics, a magnetic field is an entity produced by moving electric charges (electric currents) that exerts a force on other moving charges.\n\nThe Dynamo theory proposes a mechanism by which a celestial body such as the Earth generates a magnetic field.\n\nDynamo theory describes the process through which motion of a conductive body in the presence of a magnetic field acts to regenerate that magnetic field. This theory is used to explain the presence of anomalously long-lived magnetic fields in astrophysical bodies. In such bodies, dynamo action depends on the presence of highly conducting fluids like the Earth's liquid iron, outer core or the ionized gas of the sun. Dynamo theory of astrophysical bodies uses magnetohydrodynamic equations to investigate how the flow of the conducting materials in the interior of an object can continuously regenerate the magnetic fields of planetary and stellar bodies. It was actually once believed that the dipole, which comprises the Earth's magnetic field and is misaligned along the rotation axis by approximately 11 degrees, was caused by permanent magnetization of the materials in the earth. This means that dynamo theory was originally used to explain the sun's magnetic field in its relationship with that of the Earth. However, this theory, which was initially proposed by Joseph Larmor in 1919, has been modified due to extensive studies of magnetic secular variation, paleomagnetism (including polarity reversals), seismology, and the solar system's abundance of elements.\n\nIn the case of the Earth, the magnetic field is believed to be caused by the convection of molten iron and nickel, within the outer planetary core, along with Coriolis effect caused by the overall planetary rotation. When conducting fluid flows across an existing magnetic field, electric currents are induced, creating another magnetic field. When this magnetic field reinforces the original magnetic field, a dynamo is created which sustains itself. Similar magnetic fields are present in many celestial bodies including most stars such as the Sun (which contain conducting plasma) and active galactic nuclei.
212109
Apparently there is believed to be none now, but there may have been in the past.  Here is a quote from the link below:\n\nObservations of the magnetic fields on Mars by the Mars Global Surveyor spacecraft have revealed that parts of the planet's crust has been magnetized. This magnetization has been compared to alternating bands found on the ocean floors of Earth. One interesting theory, published in 1999 and reexamined in October 2005 in a publication by the same group, is that these bands could be evidence of the past operation of plate tectonics on Mars. However, this has yet to be proven or widely accepted and remains an area of active research.
169563
The earth's magnetic field is generated by the molten core deep inside the planet.  The magnetic North pole is positioend in the North of Canada (Churchill Bay) I believe, and this is due to an iron rich element of the magma core being near the surface.  \n\nThe magnetic North Pole is moving, and there is eveidence to show that this is quite normal over time, and that at points in history the poles have reversed.
1000213
Plate tectonics moves continents around in a cyclic pattern known as the Wilson Cycle. In about 250 million years in the future, we will again have a supercontinent.\n\nThe Paleomap Project has predicted what the earth will look like based on current evidence. The Atlantic Ocean will no longer exist, as North American will be forced up against Africa and Europe, and Indian Ocean may only remain as an inland sea.  Antarctica will again be at the South Pole and Australia will be pushed up against it. The southern part of South America will be adjoining Indonesia. \n\nThe area where the south Pacific is now is likely to have some new volcanic islands, but probably all of the currently existing islands will have been pushed up against a continent. The Pacific Ocean will be much larger than today and will cover half of the earth. \n\nHere is a map:\nhttp://www.scotese.com/future2.htm\n\nI would speculate that even further in the future as the supercontinent breaks up, it is likely that some portion of the supercontinent will move towards the South Pacific. \n\nVolcanism plays an important role in building continental plates, and is constantly adding continental material, but continental plates are composed primarily of less dense intrusive igneous rocks such as granite. Volcanoes produce extrusive igneous rocks, which do not make up the major parts of the continental land masses so volcanoes are not as important in continent building as other processes.  \n\nHere's a site that explains the Wilson Cycle:\nhttp://csmres.jmu.edu/geollab/fichter/Wilson/Wilson.html
358443
Natural magnetic variations and decay.  It is like waves of variation.
944389
I researched this as a geology student 20 years ago and has interested me since then.  By researching cores of basalt, they have a pretty good idea what the magnetic field does when it starts to shift but it is somewhat random and slow.  I remember that typically, before the switch in polarization, the poles starts to migrate in a spiral as it is doing now.  It has been an extra long time since the last switch so it is due.  I suspect that it is about to switch (within the next thousand years or so) but no one can say for certain in my opinion.  Apparently there is a period of time (100 years or so) when the field is next to zero in strength.  I saw a show on it recently that demonstrated they have learned a lot since I studied it in school.
69453
For many years scientists knew more about the surface of the Moon than about the ocean floor. In recent years, however, they have made much progress with mapping the ocean floor, using sonar detectors. Sonar stands for Sound Navigation and Ranging. Sonar detectors send out pulses of sound. When the pulses hit the ocean floor, they send back echoes. The pattern of the echoes gives a picture of what the ocean floor looks like, showing features like seamounts and trenches. \n\n\nUsually its rocky and crystalline.
699383
First of we have to understand magnetism. All magnetic objects produce invisible lines of force that extend between the poles of the object. An easy way to visualize this is to spread iron filings on a sheet of paper and place a bar magnet under the paper. The iron filings will arrange themselves around the magnet and along the magnetic field lines.\n\nIn the simplest terms, Earth can be thought of as a dipole (2-pole) magnet. Magnetic field lines radiate between Earth's north and south magnetic poles just as they do between the poles of a bar magnet. Charged particles become trapped on these field lines (just as the iron filings are trapped), forming the magnetosphere.\n\nThe origin of the Earth's magnetic field is not completely understood, but it is generally believed to be associated with electrical currents produced by convective effects and rotation in the spinning liquid metallic outer core of iron and nickel. This mechanism is generally known as the dynamo effect. \n\nBecause of the rotating outer core, this then produces an electric current, which in turn, produces a magnetic field that is also known to interact with the fluid motion to create a secondary magnetic field. Together, the two fields are stronger than the original and lie essentially along the axis of the Earth's rotation.\n\nHope this helps you out a little :)
108424
Earth's magnetic field (and the surface magnetic field) is approximately a magnetic dipole, with one pole near the geographic north pole and the other near the geographic south pole. An imaginary line joining the magnetic poles would be inclined by approximately 11.3° from the planet's axis of rotation. The cause of the field is probably explained by dynamo theory. The magnetic field extends several tens of thousands of kilometres into space as the magnetosphere\n\nThe locations of the magnetic poles are not static but wander as much as 15km every year (Dr. David P. Stern, emeritus Goddard Space Flight Center, NASA). The two poles wander independently of each other and are not at directly opposite positions on the globe. Currently the south magnetic pole is farther from the geographic south pole than the north magnetic pole is from the north geographic pole.\n\nThe field is similar to that of a bar magnet, but this similarity is superficial. The magnetic field of a bar magnet, or any other type of permanent magnet, is created by the coordinated motions of electrons (negatively charged particles) within iron atoms. The Earth's core, however, is hotter than 1043 K, the Curie point temperature at which the orientations of electron orbits within iron become randomized. Such randomization tends to cause the substance to lose its magnetic field. Therefore the Earth's magnetic field is caused not by magnetised iron deposits, but mostly by electric currents in the liquid outer core.\n\nAnother feature that distinguishes the Earth magnetically from a bar magnet is its magnetosphere. At large distances from the planet, this dominates the surface magnetic field.\n\nElectric currents induced in the ionosphere also generate magnetic fields. Such a field is always generated near where the atmosphere is closest to the Sun, causing daily alterations which can deflect surface magnetic fields by as much as one degree.\n\nMagnetic field variations\n \nGeomagnetic variations since last reversal.The strength of the field at the Earth's surface ranges from less than 30 microteslas (0.3 gauss) in an area including most of South America and South Africa to over 60 microteslas (0.6 gauss) around the magnetic poles in northern Canada and south of Australia, and in part of Siberia.\n\nMagnetometers detect minute deviations in the Earth's magnetic field caused by iron artefacts, kilns, some types of stone structures, and even ditches and middens in geophysical survey. Using the magnetic instruments adapted from airborne devices developed during World War II to detect submarines, the magnetic variations across the ocean floor have been mapped. The basalt -- the iron-rich, volcanic rock making up the ocean floor -- contains a strongly magnetic mineral (magnetite) and can locally distort compass readings. The distortion was recognized by Icelandic mariners as early as the late 18th century. More important, because the presence of magnetite gives the basalt measurable magnetic properties, these magnetic variations have provided another means to study the deep ocean floor. When newly formed rock cools, such magnetic materials record the Earth's magnetic field.\n\nIn October 2003, the Earth's magnetosphere was hit by a solar flare causing a brief but intense geomagnetic storm, provoking unusual displays of aurorae.\n\nMagnetic field reversals\n\n\n\nMain article: geomagnetic reversal \nBased upon the study of lava formations in Hawaii, it has been deduced that the Earth's magnetic field reverses at intervals, ranging from tens of thousands to many millions of years, with an average interval of approximately 250,000 years. The last such event, called the Brunhes-Matuyama reversal, occurred some 780,000 years ago.\n\nThe mechanism responsible for geomagnetic reversals is not well understood. Some scientists have produced models for the core of the Earth wherein the magnetic field is only quasi-stable and the poles can spontan
1081316
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