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A Magnetic Reversal That Lasted 22,000 Years


Doc Socks Junior

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You know how every so often people get worried about a magnetic reversal?  Well, the typical estimate as to how long it takes the magnetic field to flip is ~5000 years, give or take.  Well, throw that paltry estimate out the window, people.  The Matuyama-Brunhes transition took about 22,000 years to complete!

https://www.scientificamerican.com/article/earths-magnetic-field-reversal-took-three-times-longer-than-thought/

Quote

In their paper published today in Science Advances, Brad Singer of the University of Wisconsin–Madison and his colleagues calculate that Earth’s last magnetic field reversal took roughly 22,000 years. Previous studies had estimated the phenomenon lasts anywhere from 4,000 to 9,000 years. The new number implies the switch is a more tumultuous event than we thought. “The reversal process is way more complicated, and it lasted longer in our estimation,” Singer says. “Our study points to a more protracted and complex process for driving and propelling a geomagnetic field reversal.”

And then, the article itself.

Quote

Reversal of Earth’s magnetic field polarity every 105 to 106 years is among the most far-reaching, yet enigmatic, geophysical phenomena. The short duration of reversals make precise temporal records of past magnetic field behavior paramount to understanding the processes that produce them. We correlate new 40Ar/39Ar dates from transitionally magnetized lava flows to astronomically dated sediment and ice records to map the evolution of Earth’s last reversal. The final 180° polarity reversal at ~773 ka culminates a complex process beginning at ~795 ka with weakening of the field, succeeded by increased field intensity manifested in sediments and ice, and then by an excursion and weakening of intensity at ~784 ka that heralds a >10 ka period wherein sediments record highly variable directions. The 22 ka evolution of this reversal suggested by our findings is mirrored by a numerical geodynamo simulation that may capture much of the naturally observed reversal process.

https://advances.sciencemag.org/content/5/8/eaaw4621

Edited by Doc Socks Junior
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1 hour ago, Doc Socks Junior said:

You know how every so often people get worried about a magnetic reversal?  Well, the typical estimate as to how long it takes the magnetic field to flip is ~5000 years, give or take.  Well, throw that paltry estimate out the window, people.  The Matuyama-Brunhes transition took about 22,000 years to complete!

Even 5,000 years still gives you time to prepare.

22,000 years? At that creep does the field even lose any significant strength? 

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17 minutes ago, Piney said:

Even 5,000 years still gives you time to prepare.

22,000 years? At that creep does the field even lose any significant strength? 

It does!  I think they measured a 0.46e22 Am2 VDM during the transition.  The average over the Brunhes chron is about 6.83e22 Am2.

VDM is virtual dipole moment.  Think of it as the strength, or intensity, of the magnetic field.

Those numbers show a >90% drop in magnetic field strength! 

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And the above doesn't even take into account shorter events such as the Laschamp Event at 41,400 BP which only lasted 440 years. 

cormac

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2 minutes ago, Doc Socks Junior said:

Those numbers show a >90% drop in magnetic field strength! 

Well that can cause some radiation problems. :huh:

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4 minutes ago, cormac mac airt said:

And the above doesn't even take into account shorter events such as the Laschamp Event at 41,400 BP which only lasted 440 years. 

In terms of the discussion of 'typical' behavior you mean?  The Laschamp excursion saw a lowest VDM value of 2.46e22 Am2 (Panovska et al., 2018).  It's taken into account in the mean value, I believe.

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2 minutes ago, Doc Socks Junior said:

In terms of the discussion of 'typical' behavior you mean?  The Laschamp excursion saw a lowest VDM value of 2.46e22 Am2 (Panovska et al., 2018).  It's taken into account in the mean value, I believe.

No, of "any" behavior as most people who read about polar reversals think of the more well known of those as "the only" such activity within earth's history. They're not. 

cormac

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2 minutes ago, cormac mac airt said:

No, of "any" behavior as most people who read about polar reversals think of the more well known of those as "the only" such activity within earth's history. They're not. 

Correct.

I'm generally glad when people have "any" idea about the Earth's magnetic field reversing.

An excursion probably wouldn't be ideal for humanity either, a la Channell and Vigliotti (2019)....

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018RG000629 

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