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Thread: Earth's magnetic polarity reverses

  1. #1 Earth's magnetic polarity reverses 
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    What, you are surprised?

    Seriously, has any explanation been given for WHY Earth's magnetic polarity reverses periodically as been observed in igneous rocks? Is expected to reverse again sometime in future, can we predict when, to what degree of accuracy, what if any adverse consequences to expect and what can be done to mitigate same.

    Thanks in advance.


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    Changed the name so folks had a "clue" about the subject.


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    Most excellent! This should attract more of the desired type of feedback, thanks again to esteemed moderator! Was looking for first time at "linkback" feature, wonderful idea, TSF is great!
    The bravest are surely those who have the clearest vision of what is before them, glory and danger alike, and yet notwithstanding go out to meet it.- Thucydides
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    WYSIWYG Moderator marnixR's Avatar
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    the thinking seems to be that the flow in the liquid part of the core changes from time to time, but i'm not sure if any more in-depth explanation is currently available
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    Pondering what could be affecting such flow now. Thank you for provoking additional question. One would suspect interior of planet to be region most isolated from outside influences, must be more complex down there than suspected. Will wonders never cease...

    Van Allen radiation belts are caused by this magnetic field, at some point in reversal they must surely be affected, no?

    Van Allen radiation belt - Wikipedia, the free encyclopedia
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    WYSIWYG Moderator marnixR's Avatar
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    that was my understanding
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    A recent news item has suggested that the layout of the continents may influence flow in the liquid core. I have to find the article I read to find a reference.

    Wayne
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    If the net charge of Earth gets to ride around her axis every day, wouldn't that present our planet with the action of an electromagnet? If, Golly Gee, cosmic rays or something were to reverse the polarity of Earth's charge it might thereby produce a magnetic reversal. It might be a bad scene when and if that happens.
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    WYSIWYG Moderator marnixR's Avatar
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    i doubt whether cosmic rays have anything to do with the reversal - however, during the changeover, the strength of the magnetic field drops to zero to then re-establish itself in the other direction
    during that period all life would be exposed to more cosmic radiation than otherwise would be normal
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  11. #10  
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    Quote Originally Posted by marnixR View Post
    i doubt whether cosmic rays have anything to do with the reversal
    If the magnetic field is due to electric charge on Earth surface and atmosphere, and if cosmic rays are actually particles of positive charge, then a negative charge on Earth could be reversed under sufficient cosmic storming. The point is that charge reversal might cause a magnetic reversal.
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    Quote Originally Posted by dalemiller View Post
    If the magnetic field is due to electric charge on Earth surface and atmosphere, and if cosmic rays are actually particles of positive charge, then a negative charge on Earth could be reversed under sufficient cosmic storming. The point is that charge reversal might cause a magnetic reversal.
    And have you calculated how much charge is required and how long it would take for cosmic rays to provide that charge?
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by dalemiller View Post
    If the magnetic field is due to electric charge on Earth surface and atmosphere, and if cosmic rays are actually particles of positive charge, then a negative charge on Earth could be reversed under sufficient cosmic storming. The point is that charge reversal might cause a magnetic reversal.
    And have you calculated how much charge is required and how long it would take for cosmic rays to provide that charge?
    Give me a break! Under sufficient storming, I calculate that it would take just one third of a fortnight.
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    we may not know everything there is to know about magnetism, but one thing's for sure : its origin lies in liquid core, not in cosmic radiation
    the Van Allen belts are merely an interaction between the magnetic field and cosmic radiation (and also solar wind) where highly charged particles are kept in those portions of the upper atmosphere
    when there is no magnetic field, there are no Van Allen belts
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    Yes, the cause is magnetic field, Van Allen belts are effect. Prince regrets sowing seeds of confusion inadvertently. Do continents really have enough mass to affect core of Earth in any way? Thanks in advance to Wayne for elaboration on this question and thanks to all for comments so far.
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    Please see this GSA link for detailed data on the history of the magnetic field, as it is known today.
    I'm sorry, my responses are limited. You must ask the right question.

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    Prince is unable to identify any pattern but notices long period of continuity in Cretaceous. Many thanks! Mass of continents is very small compared to that of planetary core.

    Prince also notes that conventional magnets have not been observed to spontaneously reverse polarity.
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  18. #17  
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    Conventional magnets are not a dynamo.

    That's what is at the earth's center. There isn't a big bar magnet in there.
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    This link has an animation of the last reversal, computer simulated. WHEN NORTH GOES SOUTH: Three-Dimensional Simulation of Geomagnetic Field Reversal

    It also has the names of the researchers and modelers who have possibly best solved or described what's going on - at least, their model reproduces what we see. You can follow to their original papers etc.

    The sun also reverses polarity periodically. It's a feature of free-evolving dynamo supported magnetic fields.
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  20. #19  
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    Quote Originally Posted by MeteorWayne View Post
    Conventional magnets are not a dynamo.

    That's what is at the earth's center. There isn't a big bar magnet in there.
    Of course, thank you for pointing this out.
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    Quote Originally Posted by iceaura View Post
    This link has an animation of the last reversal, computer simulated. WHEN NORTH GOES SOUTH: Three-Dimensional Simulation of Geomagnetic Field Reversal

    It also has the names of the researchers and modelers who have possibly best solved or described what's going on - at least, their model reproduces what we see. You can follow to their original papers etc.

    The sun also reverses polarity periodically. It's a feature of free-evolving dynamo supported magnetic fields.
    Prince is much indebted, thank you!
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  22. #21  
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    The sun reverses polarity every ~ 11 years. That's the sunspot cycle. The full cycle is ~22 years when the polarity is the same. That's much different than the earth's dynamo, which goes millions of years between reversals, and has no regular periodicity.
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  23. #22  
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    Sun is a separate case of a similar phenomenon then? Would you say this description is accurate?
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  24. #23  
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    No. The causes are undoubtely completely different. The earths' dynamo is driven by convection caused by radioactive heat and slow soidificatation of the earth's solid inner core. Steller magnetic fields are a whole different (theoretical) ball of fusion driven convection than plaret's. The flip of the solar magnetic field seems to be cause by the differential rotation of the equatorial and polar regions. After 11 years or so, the magnetic fields get so twisted up, they "break" and start over with reverse polarity from the remnants of the old orientation. It's a continuous ongoing process.

    The earth's is a stochastic process. The field doesn't just flip. It starts collapsing and rebuilding in fits and starts at random spots across the field.
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    It is safe to say that most of the cerebration about this subject has been produced in innocence of the effects of an atmosphere of negative charge upon a rotating planet. The net magnetic field of Earth should be the combined result of residual permanent magnetism throughout the globe and the electromagnetic implications of the planet's electrical charge and rotation. The latter influence can impose an accumulative impact upon the former. It should seem to be more than a coincidence that the rotational poles bear such proximity to the magnetic poles. No correlation is suggested between magnetic effects on the sun and on its planets, but the entire Solar System finds a prevailing electrical influence due to nuclear activity to be expected at the core of our star. It is what our planet does with its electrical gift from the sun that determines our magnetic environment.

    A slow recovery from ignorance of such matters should find us to this day, still groping through misbegotten tomes to explain reversals of Earth's magnetic field.
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  26. #25  
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    Quote Originally Posted by MeteorWayne View Post
    Conventional magnets are not a dynamo.

    That's what is at the earth's center. There isn't a big bar magnet in there.
    There couldn't be a permanent magent there since the internal temperature exceeds the Curie point for any plausible naturally magnetic material.

    Just as a couple of random thoughts -

    Some consider that the South Atlantic Anomaly may be an early stage of the next magnetic reversal. Field strength is sufficiently low here that airlines are flying at lower altitudes to minimise crew and passenger exposure to radiation.

    The field does not dwindle to nothing. It reduces to perhsp 10% or 20% of its 'normal' value. What is more significant is that the poles become very erratic. At times the system may not be functioning as a dipole. (Hence the suspicion about the SAA.)
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