So, a question for scientific types

I’m told – a book I’m reading – that the Earth’s magnetic poles reverse, or is it the field that reverses, at times. OK, so, all of us even vaguely scientifically literate know that. The “vaguely” is the important thing here.

So, I’m told that it reverses, well, not randomly, but at unknown in advance dates. And when it does, it does so pretty quickly. But that’s quickly in geologic time. So, bumble along for a few hundred thousand, mebbe tens of millions, of years. Then the magnetic field weakens, wibbles, then over perhaps 4,000 years reverses and strengthens again.

It’s the 4 k years interregnum that interests. That the North Pole becomes the South Pole doesn’t bother me.

But the Van Allen belts, they protect us all from solar radiation. And some say that without that protection we’d all fry. I assume, but don’t know, that the Van Allen stuff is the product of the same magnetic fields that produce north and south poles. So, the reversal means 4k years of light to no Van Allen belts.


1) Why haven’t all land mammals repeatedly fried every polarity reverse?

2) They have and this is punctuated equilibrium?

3) Sure, we’ve got enough electromagnetic stuff out there that full exposure to the solar wind will fry civilisation – there’s a reason why space hardened computer chips really are different.

So, using this as a fictional device you can definitely kill civilisation and reduce population through polarity reverse. Could you though get away with it forcing the punctuation of the equilibrium and, say, get to Eloi and Morlocks as a story device?

This depends upon two assumptions. That absence of the Van Allen belts causes real problems and also that the reversal, or the weakness coincident with it, kills the Van Allen belts for that period of time.


23 thoughts on “So, a question for scientific types”

  1. Science fiction depends on some vaguely plausible “science” but that science can be complete BS. It’s just the hook for the story.

    The last magnetic reversal (cf wiki) was 780,000 years ago. Lucy was already a fossil then.

  2. 1) because the Earth’s magnetic condom doesn’t go away, it fluctuates in strength and shape all the time but a polarity flip doesn’t weaken it enough to cause extinction events. As long as the planet has a spinny iron core it’ll still be magnetic.

    Or at least, it hasn’t caused mass extinctions before, as best boffins can tell from the fossil record.

    The atmosphere also provides a lot of protection from space radiation.

    See: Mars, which lost its magnetic field entirely and subsequently leached out its atmosphere and lost its surface water, probably over millions of years

  3. It’s a while since I did any of this stuff, so from dodgy aging memory.

    1) Why haven’t all land mammals repeatedly fried every polarity reverse?

    Reversal doesn’t necessarily mean the field goes to zero and comes back the other way round. It can simply go wandering about so for a while there are east and west poles, albeit with reduced field strength. Even if the field does go to zero, we’ve got 100 miles or so of atmosphere above us as a shield from all but the most energetic particles, it’s just that the lack of field would mean auroras could occur anywhere, not just round the poles. You’d expect a slight rise in mutation rate, but probably not much more than living on Dartmoor or in Aberdeen.

    2) They have and this is punctuated equilibrium?

    Punctuated equilibrium tends to involve stonking great lumps of rock hitting the Earth, or single supercontinents forming, or glaciers reaching the equator, or 100,000 year volcanic eruptions rather then the magnetic fields wibbling about.

    So, using this as a fictional device you can definitely kill civilisation and reduce population through polarity reverse

    A nearby supernova or gamma ray burst tends to be favoured in science fiction. A GRB has the interesting effect that a large amount of the atmosphere on the side facing the GRB almost instantly turns into unbreathable NOx.

  4. probably not much more than living on Dartmoor or in Aberdeen

    On the other hand it might be a bonus for Norfolk

  5. The field is largely dipolar now but there are higher order components – spherical harmonics. If the dipolar field reduces then the other components will become more pronounced by comparison. There will still be a magnetic field controlling the flow of electrically charged particles, mostly from the Sun, but the pattern will look rather more complicated than the teardrop shape that figures in most pictures in articles on the subject.

  6. I’m going to try common sense on this. The earth’s magnetic field is driven by a dynamo. The molten regions below the crust & the core generate current. The potential is discharged through the magnetic field. So if the magnetic field disappears, where does the current go? The earth is still revolving, the dynamo is still generating. The potential – the voltage – must increase. That’s not a stable situation. Eventually the circuit must recomplete. I’d say, bearing in mind the energies involved, that “eventually” is going to be a very short one. We are, after all talking about the speed of light here, as far as electrons are concerned. I’d reckon the “eventually” might be in the order of hours or less. Then you’d get some pretty spectacular effects as the system stabilised. Auroras etc planet wide. You can get some idea from the earth’s magnetic field’s reaction to magnetic events on the sun. Common sense, again, says this must be the stable, default condition or the earth’s magnetic field would be erratic & unstable. And it isn’t. So you might lose the Van Allen belts for a brief interval & they’d fluctuate for a while. And the fact that we’re all here is indicative. Uninhibited, the solar flux would sterilise the entire planet bar the oceans in short order.

  7. “Science fiction depends on some vaguely plausible “science” but that science can be complete BS.”
    That’s good hard speculative fiction. Change something & then explore the secondary effects. So depends where the author goes with this. I sense another “disaster story”. Yawn.

  8. 1) we’re made of sterner stuff than most people think. That bit of extra radiation may result in a slightly elevated mutation rate, but this would have to coïncide with something other nasty to have a significant effect. Especially in such a short timeframe as a mere couple of millennia.
    Never forget that the most dangerous substances our body carries are water, followed by oxygen. And that we play tag with the laws of thermodynamics with those to make us work.

    2) It is not impossible.. One of the effects of the lessened magnetic field may be an increased influence of the solar wind on the uppper atmosphere, which in turn could affect climate overall.
    Again, in and of itself this isn’t enough, but it could attribute to societal collapse if things are iffy to begin with, and other stuff is happening as well.

    3) a serious solar flare could do the same,and has, much faster. The magnetic field flipping is so slow, that if a civilisation cannot harden their electronics in that timeframe, it’s not worth saving anyway.

    Morlok and Eloi? Not a chance, unless deliberate genetic tinkering is involved. Even the most stratified social structures in place for centuries have failed to produce a “docile human”. The Indians tried.. and failed. So did the Chinese. The bit where the WiPipo tried it with the imported africans was too short to even matter.

  9. A gamma ray burst also has the useful potential for conspiracy theories that “somebody” “arranged” for the “wrong”/”right” side of the earth to be hit, leaving the “right”/”wrong” side unharmed and able to take over.

  10. @Patrick

    Utterly confusing and yet also totally logical, which is great fun. When you’re naming the ends of a compass, what do you call the end that points “north”? And if the thing we therefore call a magnet’s “north” pole is, by definition, attracted to whatever’s up north … then what magnetic pole must there be up there?

    It would require a feat of great linguistic cunning to devise a scheme in which the ends of a magnet and the cardinal directions are named consistently with no contradictions or surprises.

  11. I always thought that the naming of cations and anions was asking for confusion. But then retaining the idea of the conventional “current” being in the opposite direction to the flow of electrons also invites confusion for beginners.

    Someone oughta do summink abaht it.

  12. My understanding is that the field strength does not change at all, instead the thing producing it rotates. The rotational momentum is conserved, but there are two (reasonably) stable orientations it can spin in, and it can chaotically flip between one and the other. When the reversal event happens, you won’t see the field strength reduce to zero then increase again until it’s the same as it was but opposite, instead you’ll see the two poles physically move until they’ve swapped locations.

    To see this in action, have a look at a body rotating in weightlessness (which is what the Earth’s core is doing because it surrounds the Earth’s center of gravity) on the ISS:

    I am not a geologist, so take the above with a great big “I reckon”.

  13. Not really up with the theories and there seem to be plenty but generally along the lines of the transition involves multiple poles wandering around

    Currently some publicity to the North Magnetic Pole moving from Canada to Siberia although this seems to be the Canadian North Pole is getting weaker at a faster rate than the Siberian one so the averaged point is moving

    Also some publicity to the South Atlantic Anomaly – weaker field here and this causing some problems with satellite orbits due to the effect on the van Allen belts.

    What doesn’t seem to be featuring is the South Magnetic Pole is also moving although not as fast as the North one and is now outside the Antarctic circle headed for Siberia. Crudely the NMP SAA and SMP are roughly on the same great circle.

    Maybe the bookies could establish what the odds are.

  14. The Pedant-General

    Sod the pole reversal – there’s a much more pressing concern that will occur very much sooner.

    Magnetic North has always (in my lifetime…) been West of Grid North in the UK, hence the map reading mnemonic “Grid to Mag Add, Mag to Grid get rid”.

    However, the “Grid Magnetic Angle” moves steadily eastwards and soon, horrors!, Magnetic North will be east of grid north and the mnemonic won’t work.

    What will ever do? I tell you: it’s a disaster. They’ll have to kill off everyone who learned map reading in the last 80 years!

  15. TP – you would be in trouble with the old CPL navigation exams in Australia. The exam consisted of a flight in Western Australia with diversions having to deal with different courses and winds etc. At least one sector would cross over the 0 degree variation line so failing to pick that up would lead to wrong heading and hence wrong track and ground speed. This would result in wrong calculation of the actual wind and the problems would multiply. In Later years I got to know the examiner and he had some beauties; some from the exam and some from urgent overnight guessing as what the pilot could have done to get a best guess tasking for the posse departing over the Great Australian F*** All at first light. Most had a happy ending, some didn’t

  16. The North Pole is wobbling now. Enough that airport runways have been renumbered. They are numbered to the compass directon.

  17. Given migratory species are known to use magnetic navigation it would be interesting to see the impact on them and knock effect to species that rely on them

  18. «It’s the 4 k years interregnum that interests. That the North Pole becomes the South Pole doesn’t bother me.»

    This kind of intellectual curiosity is a welcome change from the usual clever but often cravenly prejudiced economic and political stuff.
    There are two levels of answer to that, and the technical level has been discussed a bit in previous comments, and the summary is that magnetic pole reversal probably is a big deal but not a disappearance of the magnetic shield, and even that would not be entirely fatal. There are some people who think that *the earth* has reversed poles flipping on its axis at some point, but the physics of it seem “challenging” to me :-).

    The wider level is that the past is really a foreign country, on two levels:

    * The whig view of history, of constant evolutionary progress from earlier primitive states towards “the end of history” aka neoliberalism, is just silly.

    * In actual history, the past can be very different from the present, it can even be a lot better, or a lot worse, and it has been cyclical.

    As to the latter point, deforestation/reforestation, sea level changes (they have oscillated by 120 meters), shifting patterns of dry/wet climate, huge volcanic eruptions, tsunamis caused by undersea events, solar cycles and flares, etc. have changed the world much more than most people assume, and more recently than many people assume. In the longer term plate tectonics and glaciations and massive asteroid impacts have wrought immense changes. Some points that people tend to forget:

    * At various point Britain (or Italy or Taiwan) was a peninsula or viceversa an archipelago of islets.
    * North Africa used to the breadbasket of the roman empire, and in earlier times it was a lush tropical place.
    * Glaciers used to reach down to the Midlands.
    * Most of Europe used to be a large deserted forest, where entire nations wondered around unopposed.
    * Iraq used to be an earthly paradise with hundreds of thousands of gazelles roaming lush landscapes.
    * There have been (mostly because of huge volcanic eruptions) several years of “nuclear” winter even in historical times.
    * Many coastal cities are now inland because of silting, or viceversa, many interior cities are now underwater.

    It is difficult to properly understand ancient (medieval times or before) history without knowing how different geography/climate was in those times.

    Everybody is familiar with the sumerian history of the flood, and many with the indian legends of the vimana, but the weirdest and to our modern eyes the most realistic “myth” i have read is that of the “vara” of the iranians, about a period of several years of winter:

    “O fair Yima, upon the material world the fatal winters are going to fall, that shall bring the fierce, foul frost; upon the material world the fatal winters are going to fall that shall make snowflakes fall thick, even on the highest tops of mountain”
    “Therefore make thee a Vara [a hypogeum, or underground enclosure] long as a riding ground on every side of the square, and thither bring the seeds of sheep and oxen, of men, of dogs, of birds, and of red blazing fires… Thither thou shalt bring the seeds of men and women of the greatest, best and finest kinds on this earth; thither shalt thou bring the seeds of every kind of cattle, of the greatest, best and finest kinds on this earth. Thither shalt thou bring the seeds of every kind of tree, of the greatest, best and finest kinds on this earth; thither shalt thou bring the seeds of every kind of fruit, the fullest of food and sweetest of odour. All those seeds shalt thou bring, two of every kind, to be kept inexhaustible there, so long as those men shall stay in the Vara. There shall be no humpbacked, none bulged forward there; no impotent, no lunatic… no leprous.”
    “Thereupon came Angra Mainyu, who is all death, and he counter-created by his witchcraft the serpent in the river, and winter, a work of the demons… [Now] there are ten winter months there, two summer months, and these are cold for the waters, cold for the earth, cold for the trees. Winter falls there, with the worst of its plagues.”
    “In the largest part of the place he made nine streets, six in the middle part, three in the smallest. To the streets of the largest part he brought a thousand seeds of men and women; to the streets of the middle part, six hundred; to the streets of the smallest part, three hundred. That Vara he sealed up with the golden ring, and a he made a door and a window self-shining within.
    O Maker of the material world, thou Holy One! What lights are there to give light in the Vara which Yima made? Ahura Mazda answered: “there are uncreated lights and created lights. There the stars, the moon and the sun are only once (a year) seen to rise and set, and a year seems only as a day.”

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