# After the Earth's polarity reverses... **URL:** \ **Category:** Great Debates\ **Created:** [March 23, 2002, 12:37pm UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701 "2002-03-23T12:37:32Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [March 23, 2002, 12:37pm UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/1 "2002-03-23T12:37:32Z")
[This site](http://www.sciam.com/askexpert/geology/geology9/geology9.html), descibes the mechanisms of the magnetic field and the theories for polarity reversal --“we don’t know”. Suppose we wake up tomorrow and and it’s happened, north is south and south is north. What are the RW consequences? I can think of a few, mostly to do with navigation. Recalibrating magnetic compasses. Recalculating navigation tables based on compass readings. What else? Could it it have negative consequences on the small scale fields generated in transistors? Or somehow influence electric motors? Could our electrical systems fry because the energy “tries” to flow backward? Does such a global event result in a few lost backpackers and small plane crashes, or something more catastrophic? ---
**Author:** ![dalovindj](https://avatars.discourse-cdn.com/v4/letter/d/65b543/32.png) [@dalovindj](https://boards.straightdope.com/u/dalovindj)\ **Post date:** [March 23, 2002, 3:32pm UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/2 "2002-03-23T15:32:09Z")
Santa would be fucked. DaLovin’ Dj ---
**Author:** ![Duck\_Duck\_Goose](https://avatars.discourse-cdn.com/v4/letter/d/50afbb/32.png) [@Duck\_Duck\_Goose](https://boards.straightdope.com/u/Duck_Duck_Goose)\ **Post date:** [March 23, 2002, 3:45pm UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/3 "2002-03-23T15:45:37Z")
[splort] Okay, this thread is over, the DJ just put it to bed. 😃😃😃 ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [March 23, 2002, 3:58pm UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/4 "2002-03-23T15:58:37Z")
It’s not the new direction that is the problem, it’s what happens _inbetween_. There is a period est. at 200-400 years when the Earth has little or no magnetic field. And since the magnetic field shields us from solar wind and cosmic rays, bad stuff will happen. BTW, these reversals happen on a regular basis and we are due for one in the next 1000 years. Time to start stockpiling tinfoil hats. (And I bet you thought those folks were actually crazy.) ---
**Author:** ![tracer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tracer/32/20578_2.png) [@tracer](https://boards.straightdope.com/u/tracer)\ **Post date:** [March 23, 2002, 4:16pm UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/5 "2002-03-23T16:16:32Z")
ftg wrote: > [@](#): > > BTW, these reversals happen on a regular basis and we are due for one in the next 1000 years. The next **thousand** years? Where in heck did you get **that** figure? I thought a “polar flop” only came along once every couple of million years or so. ---
**Author:** ![Duck\_Duck\_Goose](https://avatars.discourse-cdn.com/v4/letter/d/50afbb/32.png) [@Duck\_Duck\_Goose](https://boards.straightdope.com/u/Duck_Duck_Goose)\ **Post date:** [March 24, 2002, 5:30am UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/6 "2002-03-24T05:30:44Z")
This website says it happens slowly over a period of about a thousand years, and that the intervals between reversals varies widely. [http://www.sciam.com/askexpert/geology/geology9/geology9.html](http://www.sciam.com/askexpert/geology/geology9/geology9.html) Also this. [http://ees5-www.lanl.gov/IGPP/EarthsMagneticField.html](http://ees5-www.lanl.gov/IGPP/EarthsMagneticField.html) > [@](#): > > After maintaining the same magnetic polarity for most of the simulation, our solution underwent a field reversal over a very short transition time of about 1000 years. Magnetic energy decreased, on the average, by about a factor of four during the 4000 years prior to the reversal and then quickly recovered after the reversal. Also this. [http://itss.raytheon.com/cafe/qadir/q1077.html](http://itss.raytheon.com/cafe/qadir/q1077.html) > [@](#): > > Is the Earth about to reverse its magnetic field? > It sure looks that way, but don’t hold your breath. It will take several thousand years… Also this. [http://science.nasa.gov/headlines/y2001/ast15feb\_1.htm](http://science.nasa.gov/headlines/y2001/ast15feb_1.htm) > [@](#): > > Earth’s magnetic field also flips, but with less regularity. Consecutive reversals are spaced 5 thousand years to 50 million years apart. The last reversal happened 740,000 years ago. Some researchers think our planet is overdue for another one, but nobody knows exactly when the next reversal might occur. Guess I’ll hold off on the tinfoil hat purchase for a while. 😃 ---
**Author:** ![Forbin](https://avatars.discourse-cdn.com/v4/letter/f/5e9695/32.png) [@Forbin](https://boards.straightdope.com/u/Forbin)\ **Post date:** [March 24, 2002, 8:43am UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/7 "2002-03-24T08:43:15Z")
A more complete answer than mine is sure to come soon, but I will point out the following. The Earth’s crust is forming in fissures at the bottom of the sea. The lava flows out and makes new earth. Some of the material created likes to align itself with the magnetic field of the Earth. If you know how quickly the lava forms new earth, and you check the existing structure (from the lava flow over x years) a determination can be made as to how long between polar magnetic reversal. Some of the material will be pointed north, and at some (x) distance other material will be pointed south. Etcetera. So far as I recall, that is how they know the durations. It’s late. I’m tired. Science class was years ago. Don’t be too hard on me if I messed this one up. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [March 24, 2002, 5:44pm UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/8 "2002-03-24T17:44:29Z")
> [@](#): > > \*Originally posted by tracer \* > The next **thousand** years? Where in heck did you get **that** figure? I thought a “polar flop” only came along once every couple of million years or so. Umm, I _didn’t_ say they happened that often. I said that the next one might be soon. E.g., March 25th happening on a Monday occurs about once every seven years. But the next one is tomorrow (as I write). There is an obvious distinction. Sheesh. ---
**Author:** ![tracer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tracer/32/20578_2.png) [@tracer](https://boards.straightdope.com/u/tracer)\ **Post date:** [March 24, 2002, 7:27pm UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/9 "2002-03-24T19:27:21Z")
Um, you didn’t say the next one “ **might** be soon”, you said that “we are **due** for one in the next 1000 years.” I’d still like to know where you got that figure. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [March 24, 2002, 10:37pm UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/10 "2002-03-24T22:37:25Z")
Some (possibly many) migratory animal species use the Earth’s magnetic field as part of their means of guidance; there could be extinctions. ---
**Author:** ![BalmainBoy](https://avatars.discourse-cdn.com/v4/letter/b/6a8cbe/32.png) [@BalmainBoy](https://boards.straightdope.com/u/BalmainBoy)\ **Post date:** [March 25, 2002, 1:55am UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/11 "2002-03-25T01:55:06Z")
Since the North magnetic pole is moving, in which direction is its movement? Think about it … ---
**Author:** ![stochastic](https://avatars.discourse-cdn.com/v4/letter/s/e19b73/32.png) [@stochastic](https://boards.straightdope.com/u/stochastic)\ **Post date:** [March 25, 2002, 6:49am UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/12 "2002-03-25T06:49:59Z")
The site listed in the OP had this to say: "The stochastic (random) nature of the process probably explains why the time between reversals on the Earth varies so much. " Hehe, I didn’t know I had such an impact upon our fine planet. Anywho, it seems the movement of the Magnetic North Pole is getting a bit of press lately: [http://www.cnn.com/2002/TECH/space/03/20/north.pole/](http://www.cnn.com/2002/TECH/space/03/20/north.pole/) From this article, it seems the pole’s movement may be picking up speed. Making the big assumption that it will continue on its present course and speed, it will be in Siberia (as opposed to it’s current location in Northern Canada) in 50 years. Here is a site by the scientist cited in the CNN article describing his research in more detail: [http://www.geolab.nrcan.gc.ca/geomag/e\_nmpole.html](http://www.geolab.nrcan.gc.ca/geomag/e_nmpole.html) And here is a NASA FAQ site I found with some good explanations about magentic north and pole reversals: [http://www-istp.gsfc.nasa.gov/Education/FAQs1.html#q1](http://www-istp.gsfc.nasa.gov/Education/FAQs1.html#q1) ---
**Author:** ![rjung](https://avatars.discourse-cdn.com/v4/letter/r/45deac/32.png) [@rjung](https://boards.straightdope.com/u/rjung)\ **Post date:** [March 25, 2002, 7:25am UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/13 "2002-03-25T07:25:55Z")
Sounds to me like another reason to push space exploration and get our collective eggs out of this planetary basket. ---
**Author:** ![heresiarch](https://avatars.discourse-cdn.com/v4/letter/h/278dde/32.png) [@heresiarch](https://boards.straightdope.com/u/heresiarch)\ **Post date:** [March 25, 2002, 10:52am UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/14 "2002-03-25T10:52:13Z")
\ The question wasn’t when it would happen or how long it would take, it was 'how would it affect us?" I don’t think it would have a measurable effect on motors or transistors. I’m not too sure about the electrical grid, but I expect that solar storms would mess them up a heck of a lot more than a change in magnetism. The only thing I can think of is induced current in Low-earth orbit satellites. I think it’s just a small voltage differential that has to be filtered out of the satellite’s electrical systems. Oh, some [migratory animals](http://www.nature.com/nsu/991007/991007-7.html) use the magnetic field to find their way around. If Santa ever got home, he might find the north pole infested with swallows and monarch butterflies. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [March 25, 2002, 2:38pm UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/15 "2002-03-25T14:38:56Z")
> [@](#): > > \*Originally posted by ftg \* > \*\*It’s not the new direction that is the problem, it’s what happens _inbetween_. > > There is a period est. at 200-400 years when the Earth has little or no magnetic field. And since the magnetic field shields us from solar wind and cosmic rays, bad stuff will happen. > > BTW, these reversals happen on a regular basis and we are due for one in the next 1000 years. Time to start stockpiling tinfoil hats. (And I bet you thought those folks were actually crazy.) \*\* A) I’m not sure that it is true that the statement that I underlined above is correct. Do you have a cite? My understanding is that the field is composed of a dipole field having a north and south pole, plus a lot of higher order modes. It is entirely possible that the energy in the dipole field is transferred to the other modes and the total field is about the same during the reversals, it just doesn’t have a definite orientation. My source for this is an article by Dr. Stephen G. Brush, University of Maryland, in the book _Scientists Confront Creationism_. Dr. Brush has this to say, “‘the magnetic dipole held is being driven destructively to smaller values by fluid motions which transform its magnetic energy into that of the near neighboring modes rather than expend it more directly as Joule heat’(cite from 1967 ESSA report by McDonald and Gunst) . In other words, the energy is being transferred from the dipole field to the quadrupole field and to higher moments rather than being dissipated as heat. This implies that the value of the dipole field could not have been much greater in the past, **since it is limited by the total magnetic energy, which does not change very rapidly.** ” B) In addition, it is my understanding that there is no evidence of any detectable disruption of life during previous reversals. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [March 25, 2002, 4:22pm UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/16 "2002-03-25T16:22:28Z")
From [Science Frontiers](http://www.science-frontiers.com/sf012/sf012p09.htm) > [@](#): > > NASA’s Magnetic Field Satellite has confirmed a trend that goes as far back as Gauss in 1830; namely, that the terrestrial magnetic field is decreasing in strength. At the rate measured by the satellite, the Earth’s field will hit zero in about 1200 years. Of course, NASA’s scientists warn that the observed decrease may only be a temporary fluctuation. The geological record seems to register a long history of magnetic field reversals, with great biological changes coinciding with the field flips. > > (Nonymous; “Magsat Down: Magnetic Field Declining,” Science News, 117:407, 1980.) > > Comment. Some field reversals have been within the time of man; 12,000 years ago and less. What happens to life forms dependent upon the earth’s field for navigation during a reversal? Can they evolve new navigation methods in only a few thousand years? (I have no idea what’s up with that “Nonymous” name.) ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [March 26, 2002, 2:50am UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/17 "2002-03-26T02:50:27Z")
> [@](#): > > \*Originally posted by heresiarch \* > **The question wasn’t when it would happen or how long it would take, it was 'how would it affect us?"** But the effects depend on how fast the change occurs, and what the intermediate state looks like. If the magnetic field disappeared for a while (say, more than a few years) I’d worry about the effects of solar radiation. Most satellites in low earth orbit will be in trouble, because they depend on magnetic force for attitude control. (Actually they usually use momentum wheels but if the satellite picks up too much angular momentum, it has to be dumped using magnetic torquers.) They could be reprogrammed if the field polarity reverses, but if the field disappears they won’t work. If the reversal happened _really_ fast, like a matter of hours, the power grid will probably sustain severe damage. Solar eruptions just jiggle the magnetic fields a bit; if the disappeared or reversed quickly, the induced current would be far greater. Magnetic sensors are still widely used for sensing the direction of vehicles and various machines. Those will be in trouble. I can’t remember if any migratory animals sense and use the magnetic field - anybody know? ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [March 26, 2002, 2:25pm UTC](https://boards.straightdope.com/t/after-the-earths-polarity-reverses/99701/18 "2002-03-26T14:25:17Z")
> [@](#): > > \*Originally posted by ftg \* > \*\*From [Science Frontiers](http://www.science-frontiers.com/sf012/sf012p09.htm) > > The geological record seems to register a long history of magnetic field reversals, with great biological changes coinciding with the field flips. > > \*\* Cites about “great biological changes …” from other than from this source would be nice. According to _Britannica_ and other sources, the results from investigations into coincident biological effects, like increased mutation, have been inconclusive. One more time, the above reference and others all agree that the evidence shows that the field that reverses is the dipole field. All other higher order fields seem to persist and even strengthen because of energy gained from the reduction in the dipole field. During the reversals the earth still has a magnetic shield against harmful particles from the solar wind. Weaker maybe and non- (or perhaps more accurately multi-) directional, but still there. Quite obviously humans have gone through such a dipole field reversal. Also, quite obviously those humans didn’t know that the field was reversing and so didn’t take, or even have the means to take, special precautions to guard against an increase in ionizing radiation. They must have made it or we wouldn’t be here to fret about the possible effects. Those extant lifeforms that have some sense that detects magnetic fields for one use or another obviously either survived, not as individuals maybe but as a species, or else have developed that capability since the last reversal. And besides that, the probability that such a reversal will occur while I’m around to see it are vanishingly small. It will be your problim, if any, not mine. Ha Ha.