Why does the Earth have a magnetic field?
925593
Don't pay any attention to the girl who said, "So we won't float away." The earth's magnetic field has nothing to do with holding us to the earth. What seems to be happening, and this is still in the theory stage, is this. The solid inner core which is almost entirely iron and the liquid outer core which is probably composed mainly of a nickel-iron alloy are rotating at different speeds and because of the turbulence in the outer core they act together as a giant electric generator (dynamo) to produce an electric current. This in turn produces a magnetic field in the same way as an electric current passing through a coil forms an electromagnet. In other words the earth is a giant electromagnet which produces a field that can be measured far into space.
1005522
The earth's magnetic poles move constantly, and on some days the North magnetic pole moves by as much as 80 km (50 miles). To see a map of this go here:\nhttp://gsc.nrcan.gc.ca/geomag/nmp/daily_mvt_nmp_e.php\n\nThe short term wandering of the magnetic poles is caused by the Sun, which emits charged particles that disturb the Earth's magnetic field. Long term movement of the magnetic poles is due to changes within the Earth's molten core, which is thought to generate an electric field that in turn forms the magnetic field. At present the North Magnetic Pole is moving more than 40 km per year towards Siberia. To see the map:\nhttp://gsc.nrcan.gc.ca/geomag/nmp/long_mvt_nmp_e.php\n\nThe magnetic field of the Earth has undergone many complete reversals. The most recent reversal was about 730,000 years before present. Here is a timescale:\nhttp://gsc.nrcan.gc.ca/geomag/nmp/reversals_e.php\n\nIn addition to the reversals, the Earth's magnetic field has what are called excursions. These are wide variations in the strength of the field and in the direction of the magnetic force. On average, these excursions are less than 50,000 years in duration. \n\nThere have been many recorded episodes of climate change, both warming and cooling, over geologic time, and so far there has been no observed correlation between changes in the Earth's magnetic polarity or 'pole shift'  with any sort of climate change. There are some scientists that proposed that changes in the Sun's magnetic field might be causing an increase in Solar wind, which in turn would affect the Earth's atmosphere and might alter the cloud formation level. If this effect reduced lower level stratus clouds, it would cause global warming, but if it reduced high level cirrus clouds the effect would be cooling. However this possible climate effect caused by the Sun's magnetic field has nothing to do with Earth's magnetic field.
329912
The magnetic field comes from the magnets that are in the generator. The magnets surround the wire coils. As the wire coils rotate, they pass by the magnets. A moving magnetic field (it's all relative, the magnetic field is still in this case) cause a current to be induced in the wire coils, thus producing electricity.\n\nI don't it has much to do with the earth's magnetic field.
1007225
An electron is a "monopole".  The reason for it having but a single extending magnetic field is that one half of an electron is formed of magnetic lines and the other half is formed into mass.  The electric field of the electron forms the equatorial line.\n\nIn larger mass, that is formed of electrons, opposite fields are formed because of opposite spin lines forming at opposite ends of a magnet.\n\nTo see this on a larger scale, consider our planet.  It has the magnetic field it does because of its rotation.  Planet Venus is almost a twin to our planet, but it has almost no spin and no magnetic field.  Planet Jupiter, a large planet with great spin, has an intense magnetic field about it that it affects spacecraft that are too long in its presence.\n\nThere are "hemiforces" moving from the poles of our planet toward the equator (called Coriolis effect).  This energy increases as one moves from the pole toward the equator because of greater mass having greater spin.  When these forces meet at the equator, they are, in force, moving opposite each other.  When passing through the plane of our equator the energy moving through the plasma forms opposite existing fields.  It's always the same.  Where there is energy present, it must give evidence of its presence in some manner.
27845
Magnetism is caused by  electrical charges in motion. This is not necessarily something unique to electrical equipment, which is the case for electromagnetism, but also for permanent magnets. It is the motion of the electrons around the nuclei, and also the spin of the electrons, that cause the magnetism in a natural magnet. The magnetic field of Earth is believed to come from movements inside the planet, where oceans and rivers of melted metals exist.\n\nI can only think of two types of magnet; natural magnet and electro-magnet.
31611
Well even though humans have known about magnets for thousands of years, the real reason they work is still somewhat mysterious. Depending on how deep you want to investigate, it can be a very complicated phenomenon. \n\nA magnet is, at its foundation, caused by the movement of electrical charge (yes this is the Biot-Savart Law). When charges (like electrons for example) move, they produce magnetic fields. If a charge moves in a loop, it creates a magnetic field. The magnetic field can be basically represented by an invisible set of arrows in space, that point in a direction. In the case of the loop, the arrows of the magnetic field will point out of the loop for a positive charge moving counter clockwise (this is the so-called "right hand rule"), and into the loop for a charge moving clockwise (some pictures are in the reference attached). \n\nThe magnetic field has a "north" end and a "south end". The little arrows from our moving charge are pointing in the "north" magnetic direction, and away from the "south" magnetic direction. It is a mysterious and interesting property of electromagnetism that two objects with fields that oppose each other, i.e., the little arrows of the field do not line up, so either the north end of one field is facing the north end of the other field, or the two south ends are facing each other, repel, or resist movement of the two objects towards each other with some force. \n\nOn the other hand, if the little arrows line up, the two objects attract each other with some force. \n\nThe forces that result from magnetic fields (and for that matter, electric fields) are fundamental forces, and part of the four fundamental forces of the universe (strong, weak, electromagnetic and gravity).  It is believed that these forces are caused, at their base, by particles passing "messenger particles" back and forth. In the case of electromagnetism, the messenger particle is a photon. How this actually works is still somewhat poorly understood, and is involved with the world of quantum mechanics, which is very counterintuitive but interesting. \n\nHowever, what is important is that we understand it well enough to make models of magnetism, and to make predictions based on those models which we can verify and use. All of electricity and electric motors are based on our ability to design systems with magnets and to be able to build and use them.
1048978
Doubtul.  The earth's magnetic field simply isn't that strong.  If it were, it would overwhelm any electronic devices on earth due to induced current.  While overall it's strong enough to protect us from harm from the solar wind and other nasty charged particles in space, it's not strong enough to harness locally for any useful work.
797174
All things with mass (made of matter) have a gravitational pull.  Larger things, like planets, have a stronger pull.\n\nThe magnetic field is caused by the movement of metal under the surface of the earth.\n\nGravity is considered by scientists to be a weaker force than magnetism.\n\nThe magnetic field helps to block harmful rays from the Sun and we would probably fry if we had no magnetic field and no protection.\n\nOf course, if we had no gravity, we would have no atmosphere and would die much more quickly.\n\nDoes that help?
773087
None of the answers given so far can be right.  The Earth doesn't spin bolt-upright, the rotational axis wobbles over time (precession).  Both poles alternately spend 6 months of the year in continuous sunlight with little or no darkness, and then 6 months in almost perpetual darkness, so it cannot be just due to the amount of sunlight available.  \nI seem to remember reading an explanation for this that relates to the Earth's magnetic field channelling solar radiation away from the polar regions toward the equator.  Presumably then the poles are colder because the magnetic poles happen to be relatively close to the rotational poles and the radiation is being channelled away from these areas ?
1086242
I think all "matters" that spin have magnetic field. I believe magnetic field is basically causing earth to have north and south pole, allowing it to spin on its axis. Earth's moon, any moon, even Sun rotates, so, it's like all planets, stars, and moons have magnetic field.
994725
An electromagnet is an iron core with wire wrapped around it so that the magnetic field that forms at a right angle to the direction of current becomes intensified in a specific location.  The reason for using insulated wire in an electromagnetic device is that it is not the current (electron frequency) moving through the wire that the engineer is interested in, but the automatic magnetic field that forms outside the wire.  This field is able to be formed, collapsed and reversed whenever one wishes to do so.\n\nA gravitational field (as our planet for example) is always one directional and the direction of energy flow is toward the core point of our planet.  Below the Moho line mass has its gravitational waves all focused toward the core point.  This means that all gravitational waves below that line pass through the very center of our planet and attract all mass directly on the opposite side, and at the same time also attracts all the heat energy of our planet to the core point.  If this were not true, then our planet would have (nearly) the same temperature throughout.
561324
No one possesses the right technology to destroy the earth's magnetic field.  Just leave it alone anyway it's always on the move.   Now the magnetic north pole i.e. where all compass really point is not the earth's North Pole, all compasses point to Prince something Island off the eastern side of Canada.  This is why on maps you will find what is called a declination angle to help in navigation.\nThroughout the earth's history, the pole has reversed every few million years.   Now, if a significant reversal should happen, that would be catastrophic in several ways.  Animals would no longer migrate the right direction, and all our technology used for navigation would have to be re calibrated.  The earth has a magetic field so that lethal amounts of solar radiation particles go around us instead of hitting the crust.
452277
Earth's magnetic field constantly fluctuates to some degree (it's weakened by about 10% since the 19th Century), but the majority of geophysicists see no hard evidence that the field is about to reverse like it's done in the past.\n\nEven should it reverse, the whole cycle takes thousands of years, and still would have little effect on our electrical power systems. Nor would planes fall from the sky, although reliance on magnetic compasses would have to be adjusted.\n\nGod should be spelled B-I-G B-A-N-G\nPBrax@netscape.com
324301
That's because the Earth's spin is caused by electromagnetics.  Something about the electrical properties of these gasses in our atmosphere causes them to be spun around faster than the rest of the Earth.
911083
The references are a good place to start learning about the earth's magnetic field.  The field on earth's surface is affected by local geologic conditions.  As your altitude increases, the earth's magnetic field looks like the field of a bar magnet.  It will cause rotation in a bar magnet that's free to rotate.  That's how a compass works.  The calculations get complex.  Try looking at a textbook on magnetism.  You'll probably see it worked out as an example.  The force in the form of a torque will be a function of the angle between the bar's magnetic axis and the background magnetic field.
129623
The dynamo theory (that the earth is maganetic) is actually due to the fact that the outer crust is molten iron.  This iron is moving around inside the earth at very high temperatures.  Physics tells us that moving metals will create  a magnetic field.  This is why we have the magnetic field around the earth.
33955
The magnetic poles have changed many times throughout earths history, and we still have the moon. Also, the moon has nothing to do with our magnetic poles. The Moon is kept in orbit by gravity, which is a not a property of our planets magnetic poles.