The last magnetic pole flip saw 22,000 years of weirdness

The last magnetic pole flip saw 22,000 years of weirdness

When the Earth's magnetic poles trade places, they take a while to get sorted.
by Scott K. Johnson - Aug 11, 2019 9:00am CDT


m kasahara / Flickr

On its face, this fact is simple: our planet's magnetic poles have traded places with some frequency over Earth's history. At points in the past, compass needles would point south instead of north. But look into the details of these transitions and things will get considerably more complicated. What exactly is it like during the times when the poles flip, for example? And what is it about the "geodynamo" of Earth's liquid iron outer core that causes this behavior?

Records of these transitions exist in several forms. Small bits of the mineral magnetite in sediment will tend to orient themselves with the Earth's magnetic field as they settle into place. Isotopes in ice cores can record changes in the magnetic field's ability to deflect away charged particles from space. And lavas—on land or the seafloor—contain magnetite crystals that are locked into place when the lava solidifies.

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A new study led by the University of Wisconsin's Brad Singer uses the latest dating techniques to put together a timeline of the most recent pole reversal (which occurred a little over 770,000 years ago) based on sequences of lava flows around the world.

History written in stone

The records come from lavas in Chile and the islands of Tahiti, Guadeloupe, La Palma, and Maui. All of them have been studied previously for tracking the history of our magnetic field, as they host multiple lava flows that each provide a snapshot around the time of the reversal. But the method used to date these rocks—based on isotopes of the element argon, which gets trapped in crystals as they solidify—has been improved enough over the last few years that the rocks were worth revisiting to get more accurate dates for each flow. The new measurements come with error bars in the neighborhood of just ±5,000 years for 780,000-year-old lavas.

The new dates help lay out an interesting timeline. Although individual records in some places have seemed to record an incredibly rapid reversal of the poles, these lavas show a complex process playing out over something like 22,000 years.

To put the whole picture together, the researchers also compiled a handful of existing magnetic records based on seafloor sediment cores and ice cores. Ice cores can only tell you how strong the magnetic field was, while sediments will record pole locations (although probably less reliably than lavas). Sediments do have the advantage of forming continuously over time, while you can only get a lava flow data point whenever a volcano feels like puking up an eruption.

Flips and flops

The researchers interpret this additional data as showing a major weakening of the magnetic field starting 795,000 years ago before the pole flipped and strengthened slightly. But around 784,000 years ago, it became unstable again—a weak field with a variable pole favoring the southern end of the planet. That phase lasted until about 773,000 years ago, when it regained strength fairly quickly and moved to the northern geographic pole for good.

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The team compared this timeline to ideas about how pole flips work. A key 2012 study proposed a common halting pattern to all pole reversals. This pattern includes a halfway flip followed by an actual full flip that reverts halfway back before stabilizing in the new orientation, all over 9,000 years or less. Rather than fitting this fairly simple pattern, the new researchers point to a 2011 model simulation they say is more similar. Although that model took 50,000 years to make the transition, it showed a matching pattern of rising and falling field strength and pole variability.

https://arstechnica.com/science/2019/08/the-last-magnetic-pole-flip-saw-22000-years-of-weirdness/

Earth's magnetic field flips much more frequently than we thought

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https://www.nationalgeographic.com/science/2019/10/earths-magnetic-field-flipped-more-times-scientists-thought/

The planet’s magnetic poles swapped places at an astounding rate about 500 million years ago, which offers clues to core formation and hints at the effects on early life.
6 MINUTE READ
BY MAYA WEI-HAAS
PUBLISHED OCTOBER 2, 2019

YVES GALLET BALANCED on a steep rocky slope in northeast Siberia, a turquoise river leisurely wending across the undulating landscape that sprawled below. But Gallet, of France’s Institut de Physique du Globe de Paris, had his face turned toward the rocks with one goal in mind: deciphering the history of Earth’s magnetic field.

This protective bubble shields Earth from radiation that’s constantly streaming from the sun. In the planet’s 4.6-billion-year history, the field has frequently flipped, swapping magnetic north and south, and some research suggests that another flip may be on the geological horizon. While fears of a looming geomagnetic apocalypse are overblown, a magnetic reversal could have many damaging impacts, from increased radiation exposure to technological disruptions, which makes understanding these historic flips more than just a scientific curiosity. (Learn more about what might happen when the magnetic poles flip.)

Now, Gallet and his colleagues have uncovered evidence of one of the highest rates of field reversals yet recorded. During this stunningly chaotic time, detailed in a recent publication in Earth and Planetary Science Letters, the planet experienced 26 magnetic pole reversals every million years—more than five times the rate seen in the last 10 million years.

Why Earth's Magnetic Field Flip-Flops
By Clara Moskowitz September 25, 2008








Earth's magnetic field may actually be two fields from separate sources.
(Image: Dreamstime)
Every so often, Earth's magnetic field flips on its head, turning the magnetic North Pole into the South Pole and vice versa.

It last happened 780,000 years ago, and is predicted to occur again in about 1,500 years ... maybe. The overall frequency is hard to predict — there was one period in Earth's history when the field didn't reverse for 30 million years.

Why these flip-flops happen at all is a great riddle, but a new hypothesis on the origins of the magnetic field could shed light on the reason.

How it works

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Earth's magnetic field is really two fields with two separate sources, argues paleomagnetist Kenneth Hoffman of California Polytechnic State University in San Luis Obispo and geochronologist Brad Singer of the University of Wisconsin, Madison, in a paper published in the Sept. 26 issue of the journal Science.

One component of the field, the stronger part, is the north-south pointing "axial dipole" magnetic field, which can be pictured as the kind of field that would be created by a giant bar magnet inside the Earth.

There is also a weaker field spread around the planet, not positioned along the north-south axis. The researchers suggest this weak field is created closer to the surface of Earth's outer core, while the stronger north-south field is produced throughout the core, including the deepest parts.

Both fields are thought to result from the movement of electrons from hot iron atoms in the convective flow of the core, which is more of a liquid than a solid. The movement of the charged particles through the planet creates a magnetic field just as the movement of an electric current through a wire does.

The researchers suggest that the sporadic reversal of Earth's magnetic field occurs when the axial dipole field weakens, leaving the weaker, more disperse field intact.

"The field is not always stable, the convection and the nature of the flow changes, and it can cause the dipole that’s generated to wax and wane in intensity and strength," Singer said. "When it becomes very weak, it's less capable of reaching to the surface of the Earth, and what you start to see emerge is this non-axial dipole, the weaker part of the field that's left over."

How can they know that?

To figure this out, Hoffman and Singer analyzed remnants of lava that poured out of volcanoes in Tahiti and Germany between 500,000 and 700,000 years ago. The lava contains an iron-rich mineral called magnetite. When the hot lava is erupted, the iron atoms' electrons spin in random directions, but as it cools down the electron spins freeze pointing in the direction of the planet's magnetic field lines.

At times when the Earth's magnetic dipole field was strong, the spins in both Tahiti and Germany pointed toward the magnetic North Pole. However, when the dipole field was weakening or preparing to reverse, the spins were left to be guided by the strongest nearby magnetic field lines from the weaker field that was left over, which were different in Germany compared to Tahiti.

More at link...
https://www.livescience.com/2897-earth-magnetic-field-flip-flops.html

Magnetic pole shock: Radiation warning as scientists make worrying discovery

EARTH’S magnetic poles could flip more frequently than scientists had previously estimated, with a radiation knock-on effect for humans and animals.



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By SEAN MARTIN
11:59, Fri, Oct 4, 2019 | UPDATED: 14:59, Fri, Oct 4, 2019

Earth's magnetic field to 'switch' in natural phenomena


In recent years, scientists have been gearing up for a potential flip in the magnetic field – a natural phenomena which had thought to occur every 200,000 to 300,000 years when the north and south poles switch. The poles attempted to swap 40,000 years ago but the process failed. As a result, the last time the poles switched place was 780,000 years ago, meaning we are long overdue a flip in the magnetic field. However, by analysing a three-million-year period around 500 million years ago, researchers discovered there were 78 pole shifts, according to the research published in Earth and Planetary Science Letters.

Radio signals from space: Astronomers investigate new radio bursts

This equates to a pole shift roughly every 38,000 years – much more frequently than the previous 200,000-to-300,000 year estimate