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Thread: Magnetic Pole Reversals

  1. #1 Magnetic Pole Reversals 
    Forum Freshman Mister URL's Avatar
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    I guess this is the place for this question, not the physics section. Maybe.

    Periodically over the life of the Earth, there has been a reversal of the magnetic poles. I have a some questions. Does anyone have the answers?

    One, do these occur rapidly, like within micro or nanoseconds? Or slowly, over centuries.

    Two, what is the effect of a reversing magnetic field on lifeforms?

    Three, a giant DC electromagnet has a static field built up around the core. When that field collapses, which it would have to do to reverse polarity, it generates a large pulse of counter EMF. Would that destroy electronics?

    I am just curious. I do not anticipate a change a comin'.

    Thanks.


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  3. #2 Re: Magnetic Pole Reversals 
    Universal Mind John Galt's Avatar
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    Quote Originally Posted by Mister URL
    Periodically over the life of the Earth, there has been a reversal of the magnetic poles. I have a some questions. Does anyone have the answers?
    They take a few thousand years. Over this period the magnetic field becomes more complex and somewhat weaker. The emergence of the South Atlantic Anomaly may be an example of the first kind of change, although it could also just be a random and meaningless fluctuation, or an unrelated phenomenon.
    Note that some of these smaller changes can occur quite rapidly, within years or months, as this example from South Africa shows.

    Two, what is the effect of a reversing magnetic field on lifeforms?
    Because the field does not disappear entirely the effects may be small. Scientists have looked for a correlation between minor extinction events and past geomagnetic reversals and found none, so it appears there is no major effect.

    Any animals dependent upon the magnetic field to navigate could get messed up, but most of these will likely have alternative navigational schemes.

    (I expect that someone is going to post a dire, gloom and doom warning about our exposure to deadly radiation. If they choose to do so, I ask in advance that they provide proper peer reviewed research to back up their claims.)

    Three, a giant DC electromagnet has a static field built up around the core. When that field collapses, which it would have to do to reverse polarity, it generates a large pulse of counter EMF. Would that destroy electronics?
    Frankly I don't know enough physics to comment authtoritatively on this. Here are my suspicions. Firstly, the fact that the field is generated in a fluid outer core may render this model inappropriate. Secondly, the extended time of the change, over thousands of years, would equally spread out and diminish in size any pulses.

    I am just curious. I do not anticipate a change a comin'
    I disagree. I think one is imminent and will arrive in the next ten or twenty thousand years. :wink:


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  4. #3 Re: Magnetic Pole Reversals 
    Forum Freshman jammer's Avatar
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    Quote Originally Posted by Mister URL
    Three, a giant DC electromagnet has a static field built up around the core. When that field collapses, which it would have to do to reverse polarity, it generates a large pulse of counter EMF. Would that destroy electronics?
    Any time you have a changing magnetic field you have electrical currents flowing in anything that can conduct electricity. The magnitude of this current is dependent on the magnitude of the magnetic field. The earth has a very weak magnetic field and so it will probably not destroy any electronics. Some very sensitive instruments may be affected however and need to be re-calibrated. Magnetic fields decay very quickly with distance, so you would need an incredibly powerful magnet in order to destroy electronics at any distances more than just a few feet. I think that most electronics are capable of handling a 5-15 Gauss field. At least from the MRI offices I have seen all of the computers are behind the 5 Gauss field markings on the floor so they are not affected.
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  5. #4 Re: Magnetic Pole Reversals 
    Time Lord
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    Quote Originally Posted by John Galt
    I think one is imminent and will arrive in the next ten or twenty thousand years. :wink:
    You mean that rhetorically. The reversal times paint the boldest picture of chaos one could wish for. They clearly correlate with nothing known.

    That's not denying what you said about transition taking thousands of years. And other good info BTW.
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  6. #5 Re: Magnetic Pole Reversals 
    Universal Mind John Galt's Avatar
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    Quote Originally Posted by Pong
    Quote Originally Posted by John Galt
    I think one is imminent and will arrive in the next ten or twenty thousand years. :wink:
    You mean that rhetorically. The reversal times paint the boldest picture of chaos one could wish for. They clearly correlate with nothing known
    I apologise for the thread necromancy, but I was catching up on things I'd missed and I noticed these comments. Could you elaborate please. I am at a total loss as to what you are saying.
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  7. #6  
    Time Lord
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    Chaos?

    If you've found a correlation, please share.
    A pong by any other name is still a pong. -williampinn
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  8. #7  
    Forum Cosmic Wizard SkinWalker's Avatar
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    What pong is saying is that there isn't enough of a pattern to say with any accuracy, let alone precision, when the next reversal could be. It could be next year or in 700,000 years.

    As to whether life would be affected, there is no good reason to think so. Some birds might get lost during migrations if the hypothesis that they use magnetics to navigate, but they'll probably sort it out.

    The mag field doesn't go away, but it does "retract" somewhat as the poles wander a bit and the Earth's dynamo "winds down." It's hypothesized that the solid inner core is spinning in a liquid outer and the direction of spin changes, which changes the poles of the mag field.

    I think I also read an hypothesis in a paper a few years ago that put the time to change poles on an order of 50 - 100 years with the north/south poles "wandering" the globe as far as the equator before the "flip."
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  9. #8  
    Universal Mind John Galt's Avatar
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    Quote Originally Posted by SkinWalker
    I think I also read an hypothesis in a paper a few years ago that put the time to change poles on an order of 50 - 100 years with the north/south poles "wandering" the globe as far as the equator before the "flip."
    There is general agreement that extensive wandering occurs before a reversal. Also the dipole may collapse and multiple poles emerge, combine and split, in complex ways. This comment is from Merrill and McFadden, Geomagnetic Polarity Transitions, Reviews of Geophysics, Volume 37, Issue 2, p. 201-226

    "The duration of an average geomagnetic polarity transition is not well known but probably lies between 1000 and 8000 years. Values outside these bounds have been reported, but we give reasons as to why such outliers are likely to be artifacts. The reversal process is probably longer than the manifestation of the reversal at Earth's surface as recorded in paleomagnetic directional data."

    I can't find anything that posits a shorter time period, but 100 or 1000, its only an order of magnitude difference.
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  10. #9  
    Forum Cosmic Wizard SkinWalker's Avatar
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    The difference is it might happen during one's lifetime or at least across a couple generations, which is useful in a cultural sense.

    I don't remember the researcher that suggested the short duration... also, it was an hypothesis based on "wandering" research. I'll see if I still have the paper over the next day or so.
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  11. #10  
    Universal Mind John Galt's Avatar
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    Quote Originally Posted by Pong
    Chaos?

    If you've found a correlation, please share.
    It was not at all obvious that this was what you meant, but on re-reading your comments I can't see why. thank you for clarifying.

    Now as to the chart: I can't find any pattern, but recent research suggests that there is. I am trying to track down the relevant paper, so far without success.
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