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Is the Earth's magnetic field about to flip ?

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Not A Rockstar

article talks about the strength of it thousands of years ago. How do we measure and know this? How does it get recorded? Where do scientists go to find out what the mag strength was, say, 100k years ago? 

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Piney
47 minutes ago, Not A Rockstar said:

article talks about the strength of it thousands of years ago. How do we measure and know this? How does it get recorded? Where do scientists go to find out what the mag strength was, say, 100k years ago? 

The polarity of certain minerals determine where the magnetic field pointed. 

http://www.geomag.bgs.ac.uk/education/reversals.html

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Not A Rockstar
36 minutes ago, Piney said:

The polarity of certain minerals determine where the magnetic field pointed. 

http://www.geomag.bgs.ac.uk/education/reversals.html

so they are saying that when this bit of lava oozes out and becomes solid it takes on the magnetics of that moment, and if we age the rock and measure that, this is how we determine what was true then in that spot?

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Socks Junior
2 minutes ago, Not A Rockstar said:

so they are saying that when this bit of lava oozes out and becomes solid it takes on the magnetics of that moment, and if we age the rock and measure that, this is how we determine what was true then in that spot?

Correct!

The tiny magnets in the magnetic minerals (magnetite, hematite) in the rock "lock in" the Earth's field as they cool. That is thermal remanent magnetization. Alternatively, as tiny magnetic grains settle in the water column at the bottom of a lake, they will align themselves physically with the Earth's field. This is detrital remanent magnetization. As you may intuitively guess, DRM is typically weaker than TRM, since it's more of a "likelihood" rather than a coercive atomic effect.

A good example of the different types is shown in the names for the last two geomagnetic excursions, where the pole wandered away from north significantly and then returned without reversing totally.

Laschamp - seen in lava flows in France 41,000 years ago.

Mono Lake - seen in a lake in Owens Valley, California 34,000 years ago.

See, both types!

At those timescales, they are probably using both volcanic and lake sediments to get their data. At these extremely short (to me) timescales, they need really granular age data to feed into their modelling. The point of the modelling is to attempt to forecast the future field.   

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Not A Rockstar

DRM sounds amazing and interesting to me! I never knew about that :)

good stuff! Thank you @Socks Junior

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NicoletteS
Posted (edited)

I hate to say it but... unlikely? I wouldn't be so sure. before this was popular knowledge in the scientific community I posited that the beginnings of this would explain current events...  ten years ago. I got a notebook and made a chart of the known history of reversals. We are way past overdue for one. The current stretch we are on of not having one is unprecedented. Sure It may not complete in our lifetime but on a cosmic scale It's only a matter of time. 

 

I kind of want to add to the above comment that our magnetic poles are always wandering, never stationary.

Edited by NicoletteS
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Socks Junior
39 minutes ago, Not A Rockstar said:

DRM sounds amazing and interesting to me! I never knew about that :)

good stuff! Thank you @Socks Junior

You're very welcome! Glad to spread the paleomagic knowledge. It's my job!

33 minutes ago, NicoletteS said:

I hate to say it but... unlikely? I wouldn't be so sure. before this was popular knowledge in the scientific community I posited that the beginnings of this would explain current events...  ten years ago.

The entrance into a reversal for us has been bandied about at least that long. And models have produced self-reversing dynamos (with unphysical boundary conditions) since the late 90s. Reversals themselves have been known about since the late 1950s - and magnetostratigraphic timescales have been based on them since the late 1960s.

33 minutes ago, NicoletteS said:

I got a notebook and made a chart of the known history of reversals. We are way past overdue for one.

Not really. About average.

33 minutes ago, NicoletteS said:

The current stretch we are on of not having one is unprecedented.

Not quite true. There have been long, long stretches of Earth history without reversals. The Cretaceous Long Normal (or Cretaceous Quiet Zone) - the field didn't reverse for 40 million years! Or the Kiaman interval in the Permian. The Moyero is more suspect.

33 minutes ago, NicoletteS said:

Sure It may not complete in our lifetime but on a cosmic scale It's only a matter of time. 

 

I kind of want to add to the above comment that our magnetic poles are always wandering, never stationary.

I would agree, but "only a matter of time" means sometime in the next million to several million years! Probably the lower end of that, given field activity recently.

They are indeed. Gilbert should have said "the Earth is a great wandering magnet".

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cormac mac airt

It should be pointed out that the following is a bit misleading:

Quote

A complete reversal of the field has happened several times before, with the last known instance occurring somewhere around 780,000 years ago.

While the Matuyama-Brunhes (AKA Brunhes-Matuyama) transition, revised to circa 770.2 ± 7.3 ka, was the last MAJOR occurrence it wasn't the last. There have since been others such as the following: 

Stage 17 Geomagnetic Excursion - circa 671 +/- 12 ka BP

“Big Lost” Geomagnetic Excursion - circa 579 ± 6 ka BP

Pringle Falls Geomagnetic Excursion - circa 211,000 +/- 13 kya BP

(Midpoints) Iceland Basin Geomagnetic Excursion - circa 192,000 BP – 189,000 BP

Blake Geomagnetic Excursion - circa 116.5 ± 0.7 kyr BP - 112.0 ± 1.9 kyr BP

Laschamp Event – Short term Polar Reversal – circa 440 years duration - circa 41,400 BP

Mono Lake Geomagnetic Excursion - circa 33,000 BP

Lake Mungo Excursion - 30,780 +/- 0.52 to 28,140 +/- 0.37 BP

Tianchi Excursion - circa 17,100 +/- 0.9 BP

Gothenburg Geomagnetic Excursion - circa 10,400 BC/12,400 C14-years BP/14,600 cal yrs BP

Pichincha Magnetic Excursion - circa 8500 BC/10,500 BP

cormac

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Socks Junior
24 minutes ago, cormac mac airt said:

It should be pointed out that the following is a bit misleading:

While the Matuyama-Brunhes (AKA Brunhes-Matuyama) transition, revised to circa 770.2 ± 7.3 ka, was the last MAJOR occurrence it wasn't the last. There have since been others such as the following: 

Stage 17 Geomagnetic Excursion - circa 671 +/- 12 ka BP

“Big Lost” Geomagnetic Excursion - circa 579 ± 6 ka BP

Pringle Falls Geomagnetic Excursion - circa 211,000 +/- 13 kya BP

(Midpoints) Iceland Basin Geomagnetic Excursion - circa 192,000 BP – 189,000 BP

Blake Geomagnetic Excursion - circa 116.5 ± 0.7 kyr BP - 112.0 ± 1.9 kyr BP

Laschamp Event – Short term Polar Reversal – circa 440 years duration - circa 41,400 BP

Mono Lake Geomagnetic Excursion - circa 33,000 BP

Lake Mungo Excursion - 30,780 +/- 0.52 to 28,140 +/- 0.37 BP

Tianchi Excursion - circa 17,100 +/- 0.9 BP

Gothenburg Geomagnetic Excursion - circa 10,400 BC/12,400 C14-years BP/14,600 cal yrs BP

Pichincha Magnetic Excursion - circa 8500 BC/10,500 BP

cormac

But those were excursions, not reversals. Brief, and they went back.

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cormac mac airt

Stage 17 Geomagnetic Excursion - circa 671 +/- 12 ka BP:  Another fully reversed flow, dated at671  12 ka, gives new volcanic evidence for the Delta/Stage 17 excursion.  https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/jgrb.50214

 

“Big Lost” Geomagnetic Excursion - circa 579 ± 6 ka BP:  One lava flow dated at 592  20 ka has a fully reversed paleodirection and most likely erupted during the Big Lost excursion

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/jgrb.50214

 

Pringle Falls Geomagnetic Excursion - circa 211,000 +/- 13 kya BP:  It is presented here the obtained high-resolution record of the Pringle Falls “aborted reversal” that has been dated by means of 40Ar/39Aranalys is yielding an age of 211 ± 13 ka [3] and correlated along a 5 km segment in the Deschutes River area in Oregon.  http://file.scirp.org/pdf/NS_2016031715173303.pdf

 

(Midpoints) Iceland Basin Geomagnetic Excursion - circa 192,000 BP – 189,000 BP:  The high southern latitude VGPs, and the recovery in RPI, imply that the Earth's main axial dipole reversed polarity during the excursion, if only for ∼1 kyr; implying that excursions can be manifested globally and are important in millennial‐scale stratigraphy.  https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2014GC005564

 

Blake Geomagnetic Excursion - circa 116.5 ± 0.7 kyr BP - 112.0 ± 1.9 kyr BP:  The ChRM exhibited normal and reversed directions recording the Blake Geomagnetic Excursion which could be radiometrically dated between 116.5 ± 0.7 kyr BP and 112.0 ± 1.9 kyr BP.  http://adsabs.harvard.edu/abs/2013AGUSMGP21A..05P

 

Laschamp Event – Short term Polar Reversal – circa 440 years duration - circa 41,400 BP:  41,000 years ago, a complete and rapid reversal of the geomagnetic field occured.  https://phys.org/news/2012-10-extremely-reversal-geomagnetic-field-climate.html

Just the first six as an example shows that "time" is not the qualifier for a reversal, direction would be, and as shown above 5 of the 6 are stated or implied to have been reversed. I think my point stands that the M/B polarity flip was the last MAJOR such event but certainly not the last. 

cormac

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Socks Junior
42 minutes ago, cormac mac airt said:

Stage 17 Geomagnetic Excursion - circa 671 +/- 12 ka BP:  Another fully reversed flow, dated at671  12 ka, gives new volcanic evidence for the Delta/Stage 17 excursion.  https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/jgrb.50214

 

“Big Lost” Geomagnetic Excursion - circa 579 ± 6 ka BP:  One lava flow dated at 592  20 ka has a fully reversed paleodirection and most likely erupted during the Big Lost excursion

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/jgrb.50214

 

Pringle Falls Geomagnetic Excursion - circa 211,000 +/- 13 kya BP:  It is presented here the obtained high-resolution record of the Pringle Falls “aborted reversal” that has been dated by means of 40Ar/39Aranalys is yielding an age of 211 ± 13 ka [3] and correlated along a 5 km segment in the Deschutes River area in Oregon.  http://file.scirp.org/pdf/NS_2016031715173303.pdf

An "aborted reversal" with "marked directional instability". That's the point!

42 minutes ago, cormac mac airt said:

(Midpoints) Iceland Basin Geomagnetic Excursion - circa 192,000 BP – 189,000 BP:  The high southern latitude VGPs, and the recovery in RPI, imply that the Earth's main axial dipole reversed polarity during the excursion, if only for ∼1 kyr; implying that excursions can be manifested globally and are important in millennial‐scale stratigraphy.  https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2014GC005564

 

Blake Geomagnetic Excursion - circa 116.5 ± 0.7 kyr BP - 112.0 ± 1.9 kyr BP:  The ChRM exhibited normal and reversed directions recording the Blake Geomagnetic Excursion which could be radiometrically dated between 116.5 ± 0.7 kyr BP and 112.0 ± 1.9 kyr BP.  http://adsabs.harvard.edu/abs/2013AGUSMGP21A..05P

 

Laschamp Event – Short term Polar Reversal – circa 440 years duration - circa 41,400 BP:  41,000 years ago, a complete and rapid reversal of the geomagnetic field occured.  https://phys.org/news/2012-10-extremely-reversal-geomagnetic-field-climate.html

Just the first six as an example shows that "time" is not the qualifier for a reversal, direction would be, and as shown above 5 of the 6 are stated or implied to have been reversed. I think my point stands that the M/B polarity flip was the last MAJOR such event but certainly not the last. 

Certainly direction is a qualifier of reversal. However, time is just as certainly a qualifier. I quote from a number of paleomagnetic reference books, bolding is mine.

Essentials of Paleomagnetism, Tauxe, 2010

Quote

When viewed over a sufficient time, the geomagnetic field reverses its polarity, by which we mean that the sign of the axial dipole term changes.

Paleomagnetism: Continents and Oceans, McElhinny and McFadden, 2000

Quote

A reversal of the Earth's magnetic field is thus usefully defined as a globally observed 180 change in the axial dipole field averaged over a few thousand years.

Geomagnetic Excursions, Laj and Channell, 2007 (from the book Treatise on Geophysics)

Quote

The duration of excursions in the Brunhes Chron (Table 2), as well as excursions with the Matuyama Chron (Table 3), based mainly on constraints from oxygen isotope stratigraphy, is usually estimated to be <5 ky. This duration is comparable with the 3 ky timescale for diffusive field changes in the Earth’s solid inner core, which must reverse polarity in order for a full geomagnetic reversal to be sustained. The fact that our estimate of excursion duration is comparable with the 3 ky time constant for inner core magnetic diffusion provides support for the suggestion by Gubbins (1999) that there is a mechanistic distinction between polarity reversals, that define polarity chrons, and excursions.

The point is, a reversal proper indicates that the axial dipole field changes sign, and then stays that way for a significant period of time. During excursions, which you're providing examples of, sure, the sign of the axial dipole field may switch, but it does not stay that way.

An interesting proposal from Laj and Channell

Quote

As higher fidelity records of excursions have become available, it appears that the majority of ‘excursions’ is manifest as directional changes through 180, followed by a return to the pre-excursional directions within a few thousand years. For example, the Laschamp and Iceland Basin excursions, although short-lived with durations of a few kiloyears, represent paired reversals of the geomagnetic field as VGPs reach high southerly latitudes for both excursions (Channell, 1999; Laj et al., 2006). ‘Excursions’ displaying low or mid-latitude VGPs, rather than high latitude reverse VGPs, probably very often reflect inadequacy of the recording medium (Roberts and Winklhofer, 2004, Channell and Guyodo, 2004), inadequate rates of sediment accumulation, and/or inadequate sampling methods, rather than geomagnetic characteristics. We therefore advocate the use of the term Microchron for brief polarity chrons with established duration less than 10^5 years (Table 1). The term ‘excursion’ would then be used only for features that represent departures from normal secular variation, for which full polarity reversal has not been established. As these features become better documented, they could then be elevated to the status of Microchron, a term that denotes a brief polarity chron

How about it? Michrochrons?

If any of the excursions you referenced were "complete reversals" as such, we would currently still be seeing a reversed magnetic field. That, I would argue, was the intent of the article when the referenced "complete reversals" - taking both the directional change and the time component into account.

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Socks Junior

I take your point that the field as temporarily reversed itself in the interim - the aforementioned excursions. I think it muddies the waters in a general consumption article to bring in the excursions. I don't think it's necessarily misleading to simplify the situation.

I think this is an interesting discussion though!

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cormac mac airt
Posted (edited)
17 minutes ago, Socks Junior said:

I take your point that the field as temporarily reversed itself in the interim - the aforementioned excursions. I think it muddies the waters in a general consumption article to bring in the excursions. I don't think it's necessarily misleading to simplify the situation.

I think this is an interesting discussion though!

As I see it a reveral is a reversal, regardless of duration. Your use of sources effectively blows excursions off as irrelevant IMO when we're actually talking durations of anywhere from 14+ human generations (the 440 year Laschamp Event, using 30 years per generation as a ballpark figure) to hundreds or even thousands of generations. Personally I find it intellectually dishonest overall, but then I'm looking at it from a human timeframe and not a geological timeframe. 

Edit to add: By intellectually dishonest I'm referring to the original post and not your take on same. 

cormac

Edited by cormac mac airt
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Socks Junior
1 hour ago, cormac mac airt said:

As I see it a reveral is a reversal, regardless of duration. Your use of sources effectively blows excursions off as irrelevant IMO when we're actually talking durations of anywhere from 14+ human generations (the 440 year Laschamp Event, using 30 years per generation as a ballpark figure) to hundreds or even thousands of generations. Personally I find it intellectually dishonest overall, but then I'm looking at it from a human timeframe and not a geological timeframe. 

Edit to add: By intellectually dishonest I'm referring to the original post and not your take on same. 

I think that is the main issue. The different timeframes. As I think I've said before, all my work is done hundreds of millions of years in the past. Because of that, the main focus is on averaging out these thousand-year timescale behaviors because (a) hard to find fine-scale records that far back and (b) to extract useful information about continental positioning we need stability of the geomagnetic field.

These general-interest articles about reversals always end up in that weird gray area - because human timescales simply are less than rounding errors on almost all geologic information - yet there is almost an intersection. Exempli gratis, the Laschamp event. Tantalizingly brief, yet still many human generations.

 

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Ogbin

I would just like to say that you guys are Super Smart. :yes:

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Not A Rockstar
6 minutes ago, Ogbin said:

I would just like to say that you guys are Super Smart. :yes:

yes, they are and classy in debating as well. I actually understood it all :) 

thank you @Socks Junior and @cormac mac airt !!

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Doug1o29

It is about to flip.  But in geologic time, "about" can be a very long time.

Doug

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