is there evidence of extinctions during pole reversal?
153621
No, based on the fossil record there is as yet no evidence of this. \n\nThere have been hundreds of these reversals in the history of the planet, not just a few.  In addition to that there are even more frequent major 'excursions' where the field changes strength. These take place as frequently as 50,000 year intervals. These excursions are quite useful in dating geologic events as they are preserved in the rock record. By combining high resolution (frequent) excursion measurements with isotopic dating of volcanic ash deposits that are less frequent many events can be dated with some precision. \n\nIt appears that most animals and birds which use magnetic fields to navigate during migration are able to adapt over the thousands of years it takes for the reversals to take place. Since the change in the magnetic field is so small for each generation of a species it appears there is no significant impact.  \n\nI've done paleomagnetic dating in areas like the Great Rift Basin of Africa.
587439
According to current thinking, there is not a reversal of rotation of the core. Rather, pole reversal is a much more complex phenomenon driven by convective flow in the outer core (the molten part) and Coriolis effect. The references below will give you an overview. According to ref. 1, the outer core is "seething, swirling, turbulent". Reversals take a few thousand years to complete, and during the reversal process the magnetic field looks like a fright wig. Currently the field is about twice as strong as normal, and is decreasing at about 1% per decade. Ref. 2 points out that although rotation alone (like that of a solid body) cannot produce dynamo currents, "disordered convection patterns can indeed produce an average dynamo field". Ref. 3 says there are many failed "attempts" at reversal before one does occur, "which is probably the reason why the times between reversals of the Earth's field are long and randomly distributed".
685382
The pole shifts are not regular, and they don't always flop a full 180. The poles drift because they are generated by a ferro-magnectic liquid that is spinning in part of our core. It doesn't spin at the same speed as the crust above it.\n(Humans are about 7-10 million years old, but it of course depends on your definition of what a human is. Upright homonid? cro-magnon? neanderthal?. The dinosaurs died out 65 million years ago. 100-200 million years ago they were in their heyday.)
503489
YES THIS IS A BIG ANSWER BUT IS USEFUL\nYes, according to the Parker Dynamo Model developed in the 1960's.\n\nMagnetic fields are generated by circulating currents of charged particles in a medium that is electrically-conducting. The sun represents a rotating gaseous body of high-temperature plasma with one type of conductivity. The Earth rotates much faster, and the liquid iron-nickel in its core has another conductivity. Jupiter rotates even faster and has yet another type of conductive core region. Parker described how the fields are generated, and derived a simple formula that describes the strength of the field AND how rapidly the field would reverse its polarity. For the sun, with some reasonable estimates for its conductivity and rotation speed, you get a polarity reversal time of about 20-50 years. For the earth, this number is between 200,000 and 500,000 years. In each case, the reversal period estimate matches pretty nearly what is actually determined from the sun spot record and from studies of terrestrial paleomagnetism.
61280
If you've ever seen a bar magnet in a pile of iron filings, you'll see that the filings will orient themselves with the magnetic field, which concentrates at the poles.  Take a look at the images in the links.  The world is similar, in that it has a magnetic polarity that makes it work like a big magnet.\n\nIonized particles fly off the sun and out toward the planets (the so-called "solar wind").  An ionized particle has a charge, and a charged particle will turn when it moves through a magnetic field.  So when these charged particles encounter the earth's magnietic field, they will begin to spin in a sort of coiled-shaped path.  The spinning stops the ions from just smaking into the earth directly, so instead it will trace the length of the magnetic field, getting dragged towards one of the poles.  As the ions cluster at the poles, one of two things might happen: it might coil so tight that it switches directions, sort of "bouncing" and making the long trek to the other pole, or it might cascade down to earth.  Those which cascade to earth will strike gases in the upper atmosphere with a lot of energy, which can cause the gases to become energetically charged.  When they release the energy, it comes out as light (pretty much the same principle as in a fuorescent light).  Due to the differences in the speed of the ions, or the differences in the types of gases encountered, the light will have different colors.\n\nThis also happens at the south pole (the other end of the magnet) in what is called Aurora Australis (the southern lights).
1103211
It doesnt reverse. You see yourself how others see you. It's not like the light waves are switching sides. . . it's the fact that they're staying on their own side that makes it look like they switched!!
307198
It is linear on intervals, on (- infinite, 0) and on (0, +infinite) but not on the whole R. \n\nTry plotting it, you get a reversed V, not a straight line.
90424
If there is no field during a reversal, the charged particles will not be spiraling down the field lines to collide with the upper atmosphere at the poles. This might have some effect on the ozone layer, which does interact with the incoming charged particles. \n\nIt was recently confirmed that the charged flux of solar storms depletes the ozone layer. With no magnetic field, this would be more evenly distributed over the entire earth rather than just at the poles (see reference). There might be less charged particle flux trapped as well, since the earth's field extends out a considerable distance. So it should allow more ozone to build up. \n\nPreviously, some had wondered if the influx of charged particles created more ozone (see reference).
513594
No, the magnetic poles are off from the geographic poles by several miles (perhaps even hundreds of miles, I don't recall exactly how much).
370987
It varies all the time. It has even completely reversed many times over geologic history, but I have never heard any good theories as to why.
32358
I don't think anyone recorded it for posterity. It has been mistakenly attributed to Zeno of Elea (circa 490 BC to 430 BC). He has some equally interesting paradoxes:\nhttp://en.wikipedia.org/wiki/Zeno%27s_paradoxes
414734
bring the magnets close to each other. If u feel any repulsion, that means u have tried joining opposite poles.\nWith this test u just come to know of the repulsive and attractive sides relative to a magnet. No qualitative nalysis of which is North pole and which is south cannot be done! But hey! If the bar magnet is painted red on one side, then that would be the north pole!
673529
north and south poles
300354
There was a report on Discovery that Earth maginetic field is shifting.this shift of poles will take thousand of years so there is no sudden change.During this change magnetic field will completely stop and there will be no defense againest solar radiation.This will cause cancer to human biengs.\nthere is a movie,"The Core" in which they shown the after effects of eliminated magnet field.
191921
There has been a study of this phenomenon done by the University of Michigan.  \n\nThe conclusion was that they entered a time warp that inverted their reality causing a rift in this universe sending them sliding around to different parallel universes for 5 years and returned only 35 minutes later in their time.  Pretty neat huh.
119325
730,000 years. \n\nThe Brunhes-Matuyama reversal happened 730,000 years ago and is a significant event for dating lots of geologic events. Since then there have been times when the earth's magnetic field has reached as little as 6% of its present strength. That excursion was 200,000 years ago. Around 700 AD, the earth's field was 50% stronger than it is now. The earth's magnetic field is hardly constant on a geologic time scale, changing strength, polarity, and wandering around on a frequent basis. At times, like during the Reunion Event, the reversals have taken place in less than 10,000 years. All of these variations make it an excellent tool for measuring the age of geologic events. \n\nI have done magnetostratigraphic analyses as part of my research.  \n\nIf you would like to download what is probably the best text on the subject of paleomag go here:\nhttp://www.geo.arizona.edu/Paleomag/book/main.htm\n\nTo see a paleomag history of the planet for the past 5 million years go to page 161 of Chapter 9 of the above book. Here is the link for Chapter 9:\nhttp://www.geo.arizona.edu/Paleomag/book/chap09.pdf
724158
Er... the theory of evoltion?  It's just a theory though.  Lots of loop holes.  :)