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I am a student of class 9. When I was going through magnetism and read that an earth is a magnet I got some doubts. My question is: is earth really a magnet? Doesn anyone have any proof that earth is a magnet? Is there a magnetic core at the center of the earth? Has anyone reached the core of the earth?

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    $\begingroup$ I feel like making a remark which is not an answer but may still contribute. I am reading a certain doubt in your question along the lines "how can we know anything about the core if we have never been there?" But that's exactly how physics work. We see effects of things we cannot explore ourselves (black holes, the sun, the deepest sea, atoms) and develop a working model of them from these effects. We don't need to know anything about the inside of the earth in order to conclude that yes, it is a magnet: it is one because we can measure its field (which is undisputed). $\endgroup$ – Peter - Reinstate Monica Nov 2 '15 at 11:24
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    $\begingroup$ @Peter Schneider: even worse, being there doesn’t help as we don’t have senses to decide whether the thing we see, touch or smell is a magnet. $\endgroup$ – Holger Nov 2 '15 at 13:22
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    $\begingroup$ Last question is a little out of scope for Physics, but no, no one has reached it yet, too high pressure and temperature. Deepest point reached is en.wikipedia.org/wiki/Kola_Superdeep_Borehole, deepest point is about 12 000m (~40 000 ft) $\endgroup$ – Viktor Mellgren Nov 2 '15 at 15:16
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    $\begingroup$ nope, compasses work by magic. $\endgroup$ – Apologize and reinstate Monica Nov 2 '15 at 22:44
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    $\begingroup$ "A magnet you can attach your refrigerator to" - Lester, World of Beakman $\endgroup$ – jean Nov 3 '15 at 10:21
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Earth has a magnetic field. You can verify this yourself; it is why a compass works. Just take any magnet and hang it carefully from a string. As long as there's nothing else magnetic around and it's well-balanced and free to rotate, it will line up with Earth's magnetic field.

We have measured the Earth's magnetic field all over the surface and up into outer space using satellites. The magnetic field is fairly weak; on the surface of Earth it is about a hundred times weaker than a simple refrigerator magnet, which is why we don't notice it often in daily life. No one has reached the core of the Earth; our knowledge about it is inferred using physics, mathematics, and geology.

Whether or not Earth "is a magnet" is a semantic issue, but the existence of the magnetic field is not in doubt. This magnetic field is important to life on Earth because it deflects a lot of the harmful radiation that reaches Earth through space. It is also responsible for the auroras that appear near Earth's poles.

The magnetic field is not caused by a part of the Earth being magnetized like a refrigerator magnet. Instead, it is caused by a the motion of liquid metal inside the Earth, which causes currents that generate a magnetic field. The metal moves because the Earth is different temperatures at different spots, because of gravitational forces, and because of Earth's rotation. This phenomenon is called "convection" and you can see it when you boil a pot of water.

The physics behind generation of Earth's magnetic field is called "magnetohydrodynamics". The equations involved are very complicated and difficult to solve, but there is little doubt about the fundamental mechanism. By examining old rocks, we know that Earth's magnetic field periodically switches directions. We can write computer programs that simulate Earth's magnetic field, but there is still uncertainty about details such as when the next reversal will be or how long the field will last.

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    $\begingroup$ You know I knew all about magnetic dipoles and magnetic field due to currents and stuff but I never realized that a floating magnet would align with north. It's important to go back to your roots, I suppose. $\endgroup$ – Faraz Masroor Oct 31 '15 at 21:04
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    $\begingroup$ Wow, what a beautifully phrased answer that is perfectly fit to the level of the question! $\endgroup$ – hyportnex Oct 31 '15 at 22:02
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    $\begingroup$ Joined this site (after lurking for a while) to upvote this answer and @hyportnex comment. $\endgroup$ – Ethan Bolker Nov 1 '15 at 13:46
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    $\begingroup$ Might make it a little easier to visualise; A simulation of the Earth's magnetic field at 100 years/second. $\endgroup$ – Basic Nov 2 '15 at 2:48
  • $\begingroup$ I guess it's also worth pointing out that the magnetic field of Earth is much more complicated than a simple dipole magnet. For example, there is no "magnetic north pole" where your compass would point regardless of your position. $\endgroup$ – JiK Nov 3 '15 at 14:20
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Yes, Earth does have a magnetic field(check it out with a compass!).
In geology, they explain this in this way: The Earth's core is divided between the inner and outer cores. The inner core is solid because of the very high pressure. The outer core, although it also has high pressure, it is not as high as the inner core and thus it is not solid, but fluid. But the fluid is composed of molten iron and nickel, so its highly conductive. Due to the Earth's rotation(via the Coriolis force) and the temperature gradient inside the outer core, we have a flow of the fluid outer core. Because the conductive material is moving(rotating really, check Wikipedia), the movement is really a current and thus via Faraday's induction law, we get a magnetic field. Note that the current is also affected by the inner core but if you want more details about this check Wikipedia, as this is really not part of the answer.
Nobody has been to the center but geologists know that the magnetic field certainly has to do with the aforementioned factors(like Earth's rotation) because many numerical models have successfully reproduced some of the characteristics of the Earth's field. So, while we know we are on the right path, we are not 100% sure that this is the full explanation.

EDIT: the fact that there is in fact a magnetic field can be seen from Paleomagnetism, which is the study of the record of the Earth's magnetic field in rocks, sediment, or archeological materials(as Wikipedia puts it). So, we know the age of rocks from the direction and magnitude of the magnetic field during the time when the rock was formed.

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No there is no magnet inside earth. I mean there is not any magnet like we see in our surroundings.Earth itself is a magnet or not is upto you, because there is no direct answer to it. As explained by some scientists there are convectional currents of molten iron and nickel in core which generates magnetic field around earth.

Nobody truly knows the real reason behind Earth magnetism. But still we know earth is magnetic. the best proof of it is magnetic compass.

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    $\begingroup$ an electromagnet is still a magnet. $\endgroup$ – Jasen Nov 1 '15 at 8:26
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    $\begingroup$ @steveverrill: I wonder if the poster meant convection currents & a translation error occurred? $\endgroup$ – Kyle Kanos Nov 2 '15 at 18:34
  • $\begingroup$ yeah, that was translation error. $\endgroup$ – Anubhav Goel Nov 3 '15 at 15:53
  • $\begingroup$ @steveverrill: then you would say even light and every particle in this world is magnetic, since magnetic waves exist in every interaction in this world. $\endgroup$ – Anubhav Goel Nov 3 '15 at 15:57
  • $\begingroup$ Answer much improved, I've upvoted it. Yes, particles are magnetic. Light / electromagnetic radiation is a means by which changes in magnetic fields are propagated. This is particularly apparent in the radio frequency range. $\endgroup$ – Level River St Nov 3 '15 at 18:26
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The difference between a magnetic substance and non-magnetic substance is their difference in spin alignment or we may call it spin polarity. That is why we have ferromagnets, diamagnets and antiferromagnets. You can google for more information on source of magnetism.

The Earth behaves as a magnet because it affects those magnetic substances (e.g. compass or any bar of magnet) and its magnetic field is ordered regularly. There is no doubt that the Earth is like a bar of magnet! The core is a dynamo of electrical current. And electricity and magnetism are two faces of the same coin. You can read Maxwell's unification theory. It is simple and understandable with your current knowledge because algebra is enough to understand it.

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