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Earth’s Magnetic Pole Reversal – Don’t “Flip Out”!

Schematic illustration of Earth's magnetic field. Credit/Copyright: Peter Reid

Have you heard or read stories about how Earth will some day reverse its magnetic poles? If you have, then chances are very good you’ve also heard this perfectly normal function of our planet could spell disaster. Before you buy into another “end of the world as we know it” scenario, let’s take a look at the facts.

For the record, we know that Earth’s magnetic field has changed its polarity more than once in its lifetime. For example, if you could step back in time some 800,000 years ago with a compass in your hand, you’d see the needle pointed to south – instead of north. Why? Because a compass works on magnetic fields, its needle directs you to the magnetic pole, measured as either positive or negative. The markings on the modern compass dial would be incorrect if the polarity of Earth’s magnetic fields were reversed! Like a witch hunt, many would-be prophets say natural occurrences like this might signal doom… But could their theories be correct? Unfortunately for hyperbole, the geologic and fossil records from past reversals show the answer is “No.” We’ll still be around.

Just like the Sun reversing its magnetic poles, Earthly switches are just a part of our planet’s schedule. During about the last 20 million years of our formation, Earth has settled into a pattern of switching magnetic poles about every 200,000 to 300,000 years… with a period of twice that long since our last reversal. And, it’s not a thing that happens rapidly. Magnetic pole reversal takes up to several hundred thousands of years to complete. The fields blend together and magnetic poles pop up at odd latitudes as it happens. It’s not that scary! Scientists say that Earth has reversed its magnetic field hundreds of times over the last three billion years and have sped up slightly with time.

How do we know about the impacts of magnetic pole reversal? We take a look at the deep evidence – sediment cores taken from the ocean floor. These samples are perfect fossil records which show us what direction the magnetic field was pointed in as the underwater lava emerged. These ancient flows were magnetized in the field’s direction at the time of their creation and exist on either side of the Mid-Atlantic Rift where the North American and European continental plates are moving away from each other.

“The last time that Earth’s poles flipped in a major reversal was about 780,000 years ago, in what scientists call the Brunhes-Matuyama reversal. The fossil record shows no drastic changes in plant or animal life.” says NASA’s Patrick Lynch. ” Deep ocean sediment cores from this period also indicate no changes in glacial activity, based on the amount of oxygen isotopes in the cores. This is also proof that a polarity reversal would not affect the rotation axis of Earth, as the planet’s rotation axis tilt has a significant effect on climate and glaciation and any change would be evident in the glacial record.”

A schematic diagram of Earth's interior and the movement of magnetic north from 1900 to 1996. The outer core is the source of the geomagnetic field. Graphic Credit: Dixon Rohr

Unlike a hard-wired magnet, Earth’s polarity isn’t constant – it moves around a bit. The reason we have a magnetic field is our solid iron core surrounding by hot, fluid metal. According to computer modeling, this flow creates electric currents which spawn the magnetic fields. While it’s not possible at this point in time to measure the outer core of our planet directly, we can guess at its movement by the changes in the magnetic field. One such change has occurred for almost 200 years now… Our northern pole has been shifting even more northward. Since it was first located, the pole has shifted its place by more than 600 miles (1,100 km)! What’s more, it’s speeding up. It would seem that it’s moving almost 40 miles per year now, instead of the 10 miles per year as recorded in the early 20th century.

Don’t be fooled by those saying a magnetic pole reversal would leave us temporarily without a magnetic field, either. This is simply isn’t going to happen and we’re not going to be exposed to harmful solar activity. While our magnetic field goes through weaker and stronger phases, there is simply no evidence to be found anywhere that it has ever disappeared completely. Even if it were weakened, our atmosphere would protect us against incoming particles and we’d have more auroral displays at lower latitudes!

So, go ahead… Sleep at night. Earthly magnetic pole reversal is a normal function of our planet and when it does happen its effects will be spread out over hundreds of thousands of years – not flipped like a pancake.

Original Story Source: NASA Earth News. For Further Reading: Earth’s Inconstant Magnetic Field..

About 

Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.

Comments on this entry are closed.

  • squidgeny December 5, 2011, 4:19 PM

    Earth has settled into a pattern of switching magnetic poles about every 200,00 [sic] to 300,000 years… with a period of twice that long since our last reversal.

    I find that remarkably odd… is that just a statistical blip and if so, just what are the chances? Or is it thought to have a very specific cause, and if so are there any compelling theories?

    • Anonymous December 5, 2011, 5:04 PM

      The Earth’s magnetic field is generated in the interior by various processes which generates current. For some reason the “dynamo” has these flips, which occur episodically or quasi-periodically. The direction of the Earth’s magnetic field in the past is known from the magnetization fingerprint it leaves behind with molten basalt spreading out from the mid-Atlantic ridge. The material as it solidifies has its magnetization direction parallel to the Earth’s magnetic field at that time. If the rate of this deposition has been constant then it is possible to time-log past magnetic reversals.

      LC

      • canderson December 5, 2011, 7:37 PM

        Actually, the rate of deposition need not be constant–we can date the rocks using radioisotopes.

        • Anonymous December 6, 2011, 2:24 AM

          Indeed that is the case. It turns out that radiometric dating finds that the rate of rift spreading is fairly constant.

          LC

      • squidgeny December 6, 2011, 3:45 PM

        I’m not sure that answers my question (it seems to just repeat the article), but perhaps I didn’t phrase it well. What I’m essentially trying to ask is:

        Why has it been 800,000 years since the last flip if it flips every 200,000 – 300,000 years?

        • Anonymous December 7, 2011, 10:49 PM

          according to the article , the earth has settled into that pattern only for the last 20 million years. if you look at a chart for the time period before that, you’ll see that there are frequently times in which it occupies one state for longer periods and there is no long term pattern for when it will switch.

    • Jonathan May December 5, 2011, 9:15 PM

      How about this for a model? http://static-images.intheproshop.com/product-images/ebonite/bowling-balls/500/mission-2-0-26558.jpg

      It’s a pretty good bowling ball, with the center of mass that is imbalanced. As it rolls down the lane, it tries to balance with the rotation, causing the ball to ‘flare’ and turn over, hooking at a certain spot. A bowling ball however doesn’t have a viscous center of molten rock between the core and the surface, but..!

      Perhaps the core of our planet is irregular and dynamic, and as the Earth spins it’s naturally trending towards stable gyroscopic motion. Depending on whatever shape the core takes, a number of different things could happen.

      Somehow after seeing diagram after diagram of neat concentric perfect circles since a child, I honestly doubt things are that clean. I do recall seeing a ‘gravity map’ of the planet taken from a satellite, and I assumed it would represent various densities of matter near the surface.. As I was writing this though, it seems like in that data should also be the density and distribution of matter in the core. Hmm! Now to figure out how to subtract the surface and mantle from the measurement.

      • Wezley Jackson December 7, 2011, 12:26 AM

        Interesting!!! See my general post comment above.. This seems like a very plausible place to investigate as a starting point…

  • Dan Sanderson December 5, 2011, 4:23 PM

    I find it difficult to imagine what direction our North Pole is shifting. It’s already at North, by definition, so it can only be shifting southwards, but that’s not the case either, as where ever it is it’ll be North. Bit of a head scratcher. I suppose, given time, we’d have to agree on the switch over day where we’d stop referring to the North Pole as the North Pole and start calling it the Eastern Pole, or however far it has moved. 40 miles a year is quite a lot.

    • canderson December 5, 2011, 6:27 PM

      It’s able to move north (north-northwest, actually) because the north magnetic pole isn’t located at the north geographic pole–it’s in NE Canada. That’s why surveyors have to correct magnetic compasses–the difference between magnetic north and true north at a given location and time is called the magnetic declination, and most compasses have a moveable ring to allow for the correction.

      And, when you consider that the circumference of the Earth is almost 25,000 miles, 40 miles/year (the number I’ve seen is 34-37/year as of 2009) is less than 1% of the distance from the equator to the geographic pole.

      Finally, it’s probably not wise to assume that the drift rate is constant. We’re talking about a magnetic field that can only be modeled with supercomputers due to its enormous complexity. I’d be very surprised if the current drift rate is maintained over even a decade timescale (e.g. the average drift rate in the 20th century was less than 1 mile/year).

  • HeadAroundU December 5, 2011, 4:32 PM

    Tell me about the end of the world as we don’t know it. That catchphrase is getting deep. :D

    Alright, so it’s not flip-flopping like Republicans.

  • HeadAroundU December 5, 2011, 4:32 PM

    Tell me about the end of the world as we don’t know it. That catchphrase is getting deep. :D

    Alright, so it’s not flip-flopping like Republicans.

  • Leszek O December 5, 2011, 5:56 PM

    This article just shows how little we know about that process. If the speed of the reversal is increasing, then it is possible that it can move much faster then it is moving now.
    How can we be sure that it will take thousands of years? Maybe because it is so much overdue the reversal will start to happen really fast – like within our lifetime.
    It might be too fast for our planets biota to adjust. We might experience massive extinctions. Think about migrating birds for instance.

    • Anonymous December 6, 2011, 5:54 PM

      So basically, you are clueless. You are just making things up to fit your claim.

    • Torbjörn Larsson December 6, 2011, 7:52 PM

      Did you read the article? There is little to adjust to.

      The only effects that would be noticeable is for species that uses magnetic compasses. Some birds do that, but not exclusively.

      Biologists are busy uncovering mechanisms that enable them to adjust migrations in general, historically and now. That is why they can handle AGW somewhat, despite climate zones migrating at a clip of ~ 6 km/year.

  • canderson December 5, 2011, 6:10 PM

    “…and when it does happen its affects will be spread out…”
    I think you mean “effects.”

    • IVAN3MAN_AT_LARGE December 5, 2011, 7:50 PM

      I’ve already e-mailed a note to Tammy about that.

      • Anonymous December 6, 2011, 12:12 AM

        Tammy Tammy Tammy, tis time to hang it up. Your credibility as a science journalist has sunk to new lows. At least one spelling, punctuation or sentence structure critique per article now, tsk tsk tsk. It is obvious that the grammar patrol here would prefer articulate writing skills as apposed to up to date and informative science news that you so brilliantly and of course, professionally, provide for us viewers. Perhaps you should have majored in English and the arts rather than Astronomy and related math and sciences disciplines.

        • Anonymous December 6, 2011, 8:34 AM

          I always enjoy Tammy’s features – they are down to Earth and accurate. She tends to concentrate on observational astronomy or aspects of the science relevant to “backyard astronmers”.

          Her output is fantastic and is not surprising that the odd typo creeps in.(Only a proportion appears in UT) Compare with any newspaper!

          So keep it up Tammy we value your contributions

          Brian Sheen

        • Anonymous December 6, 2011, 2:12 PM

          Ivan has always offered constructive criticisms for UT authors. He never has a bad attitude about it and I believe he just wants to help.

          Tammy and the rest of UT are excellent at what they do, and I have no doubt they put a lot of time and effort into it. They are human, and mistakes happen. They do a very good job about correcting mistakes, and often those mistakes are also found in the source articles and press releases.

          Science blogs have very little room for error, and any errors that do happen tend to be noticed by many. Consider many of the people who post here are professors, researchers, or scientists themselves, and are therefore more likely to notice such things. I think this is a good thing, and I often look at articles specifically to see what these posters have to say. It’s a community, and that’s good.

          • Anonymous December 6, 2011, 6:39 PM

            Okay here goes…I find these interjections (Yo!) into the comment stream as annoying as TV commercials and pop up ads. I certainly agree that errors that alter or distort the integrity of the “original” material should be brought to attention however, injecting comments to point out simple spelling or punctuation nuances that clearly have no such altering “affects”, is, IMHO, unnecessary not to mention distracting. So there!

          • Anonymous December 7, 2011, 10:59 PM

            good point. you’d expect one that holds others to such exacting standards would be sure to create grammatically perfect masterpieces with each post.

            …but to to be fair, in this example he had politely emailed tammy with his correction, sparing us the irritation of reading it. he only commented when it looked like a different spelling nazi might be trying to steal his thunder.

          • IVAN3MAN_AT_LARGE December 7, 2011, 11:35 PM

            There’s a difference between formal (e.g., an article) and informal (e.g., comments) writing. ;-)

          • Anonymous December 8, 2011, 12:32 AM

            i never claimed otherwise.

          • Anonymous December 8, 2011, 12:39 AM

            now turn that sharp eye of yours to this example. although there are a few grammatical mistakes that most people honestly don’t care about, can you spot the major error?

            “Earth has settled into a pattern of switching magnetic poles about every 200,000 to 300,000 years… with a period of twice that long since our last reversal. And, it’s not a thing that happens rapidly. Magnetic pole reversal takes up to hundreds of thousands of years to complete.”

          • IVAN3MAN_AT_LARGE December 8, 2011, 1:08 AM

            The major error is the use of the pronoun “our” – which is the possessive case of “we” – instead of the correct possessive pronoun “its” in that context.

            Also, (a minor error) in formal writing, one should avoid starting a sentence with the conjunction “And”.

          • Anonymous December 8, 2011, 1:19 AM

            you missed it.

          • Anonymous December 8, 2011, 1:23 AM

            it’s a mistake that alters the intended meaning of the statement and creates an error. you seem like a fairly scientific fellow, i’m surprised you didn’t notice.

          • IVAN3MAN_AT_LARGE December 8, 2011, 2:01 AM

            Do you mean the missing “its” between “switching” and “magnetic poles”?

          • Anonymous December 8, 2011, 2:39 AM

            i’m sorry. i’ll stop teasing you now. in the final sentence of the quote, unless tammy has her own special theory of how long a pole reversal event lasts, it should read “… hundreds OR thousands of years to complete”. i read somewhere that the average time is believed to be about seven thousand years based on current (inconclusive) observations.

          • IVAN3MAN_AT_LARGE December 8, 2011, 3:01 AM

            D’oh! I see now… that’s what happens when one drinks strong lager while reading articles – the mind sees what it wants to see! ;-)

  • Anonymous December 5, 2011, 6:16 PM

    Tammy, there are a few recognized reversals that took tens of years, not thousands. Eg, http://www.newscientist.com/article/mg20727765.000-second-superfast-flip-of-earths-poles-found.html

  • Anonymous December 5, 2011, 10:50 PM

    Okay, very interesting and I’m glad someone broached this topic but WHY?!?1 Does the core flip over in its metallic womb? Do we have any theories as to how and why? It’s regular but erratic…and speeding up. Any thoughts as to how long the pattern will last? Does it coincide with the age of the planet, the temperature of the innards? Is there any reason to believe the strength of the field actually goes away before it comes back in the south? Or do all our compasses just point to Equador for a while?

    • Torbjörn Larsson December 6, 2011, 7:55 PM

      While the dynamo mechanism is accepted by most, there are AFAIK no detailed models that can predict polar migrations.

      The problem seems to be that the core is just large and hot enough to not be amenable to laboratory scale models which could inform computer models. Or at least, not without a lot of funding.

  • Jeremy Arena December 6, 2011, 12:47 AM

    Any concern of vertical uplifts exposing two more stars in our solar quadrant from a passing star system(8 dwarf sized star chain) theory instead of polar reversal?

    • Torbjörn Larsson December 6, 2011, 7:58 PM

      Um, what? I can’t parse that but FWIW:

      – Earth magnetic field is internally generated and not directly affected by other systems. It is somewhat affected by orbital changes, but changes from passing stars that would affect the orbit would probably have worse effects on the climate et cetera.

      – Plate tectonics (causes crust “vertical uplift” by subduction et cetera) is not affected by the magnetic field.

  • Durgadas Dutta December 6, 2011, 6:44 AM

    If you rotate a bar magnet very very slowly ,then after a few billion years it will reverse its pole positions and we my think of flipping as the effect around is not detected in billion years. Same think is happening with earth, read theory of gravitoethertons which gets focussed at center of earth causing magnetism due to monomagnetic coupling of gravitoethertons. Do not think it is flipping like a bulb light off and on.

    • Torbjörn Larsson December 6, 2011, 8:01 PM

      At least 5 major problems with that:

      – The dynamo theory predicts the magnetic field already. You can’t suppress that.
      – Magnetic monopoles have never been observed.
      – EM doesn’t couple to gravity.
      – There is no aether.
      – No one has observed “gravitoethertons”.

  • Anonymous December 6, 2011, 8:35 AM

    NB astronomers – typical.
    Roseland Observatory

  • Anonymous December 6, 2011, 9:11 AM

    All of the trillions of stable magnetic field’s out there in the universe and I’ve got to pick the one that flip flops… great~ Guess I’ll make the best of it and start a compass repair business?

  • Bharath Purtipli December 6, 2011, 4:14 PM

    Yeah, right, WHY should it reverse ? I don’t understand !
    And, I’d love to see aurorae over my house !

    • Torbjörn Larsson December 6, 2011, 8:02 PM

      AFAIK it is an open problem, see my comment to Peristroika.

  • Bharath Purtipli December 6, 2011, 4:14 PM

    Yeah, right, WHY should it reverse ? I don’t understand !
    And, I’d love to see aurorae over my house !

  • Minor Planet Center December 6, 2011, 11:32 PM

    So, go ahead… Sleep at night.

    No! I refuse! I’m an astronomer, dammit! :-)

    —JL Galache

  • Wezley Jackson December 7, 2011, 12:23 AM

    Another great informative article Tammy, thank you!

    I find this seeming contradiction curious (quoting article):
    // start quote
    //
    During about the last 20 million years of our formation, Earth has settled into a pattern of switching magnetic poles about every 200,000 to 300,000 years… with a period of twice that long since our last reversal.

    Scientists say that Earth has reversed its magnetic field hundreds of times over the last three billion years and have sped up slightly with time.
    //
    //end quote

    OK, so if the magnetic field reversals have sped up over time as a trend, why has the last reversal taken place at over double the average interval with only hints a reversal initiation could be imminent?? Quite a statistical anomaly and huge variation? Do any scientists have any ideas or proposed hypothesis on why this might be so???

    Thanks,

    Wezley

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