Mystery; Earth Magnetic Field Flip-Flopping

The Earth's magnetic field, magnetic poles and
geographic poles. Click to enlarge this image.
Earth's Magnetic Field image via Shutterstock
Earth's magnetic field reversed extremely rapidly
soon after modern humans first arrived in Europe,
completely flip-flopping in less than a thousand
years, new research suggests.
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These findings, detailed Oct. 15 in the journal Earth
and Planetary Science Letters, could shed light on
how and why magnetic field reversals happen, and
how they leave Earth vulnerable to solar and space
radiation, the study scientists said.
Earth's metal core acts like a giant magnet that
emanates a magnetic field with two poles, north and
south. These two magnetic poles very roughly match
where the planet's geographic north and south poles
lie, which mark the axis on which Earth spins.
"The Earth's magnetic field is a highly dynamic
feature," said researcher Norbert Nowaczyk, a
paleomagnetist at the GFZ German Research Centre
for Geosciences. "Its intensity pulsates between
values 50 percent higher than today, or 90 to 95
percent lower than today."
In addition, every several hundred thousand years,
Earth's magnetic field reverses — a compass that
would have pointed north would instead aim south.
These flips are captured by magnetically sensitive
minerals in cooling lava that are literally set in stone
pointing to where the poles were at that particular
moment in Earth's history. ( Earth Quiz: Mysteries of
the Blue Marble)
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Failed reversals
Full reversals of the magnetic field usually take
millennia to finish, based on those frozen rock
records. However, scientists now find that 41,000
years ago, shortly after modern humans first entered
Europe, the magnetic poles flipped and flipped again
in less than a millennium.
Scientists analyzed data in sediment from the floor of
the Black Sea and compared it with other data from
the North Atlantic, the Southeast Pacific and around
Hawaii. Surprisingly, they found the Earth's magnetic
field took about 200 years to flip, during which time
it was just one-twentieth as strong as it is today.
"Former ideas about a field reversal deal with
durations of 2,000 to 5,000 years," Nowaczyk told
OurAmazingPlanet.
Earth's magnetic field stayed reversed for only 440
years, during which time it was just one-quarter as
strong as it is today. The magnetic poles then flipped
back to approximately where they were before over
the course of about 270 years. The flip-flop overall is
known as the Laschamp event, after the area in
France where evidence of it was first discoveredin the
1960s. These new findings reveal how quick this
reversal was.
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The brevity of this flip overall suggests "it might
represent a so-called aborted reversal," Nowaczyk
said. "This means the geomagnetic field tried to
reverse, but fell back." Such aborted reversals, also
known as excursions, may have happened at least a
dozen times during the last 780,000 years since the
last full reversal, he explained.
Magnetic field shield
Earth's magnetic field helps protect the planet from
energetic particles streaking out from deep space
and the sun. During the Laschamp reversal, Earth
was significantly more vulnerable to radiation from
space, judging by higher levels of radioactive
beryllium seen in ice samples from Greenland,
Nowaczyk said.
Such radiation poses a particular threat in our
modern world, so understanding these reversals is
helpful to better understand the threats from space.
"Communication and GPS satellites might be
damaged when the cosmic rays are less shielded by
the geomagnetic field," Nowaczyk said. "Therefore, it
is important to know how dynamic the geomagnetic
field is in time and space. We need to know how fast
changes in intensity, and thus shielding ability, can
happen."
Earth's magnetic field is generated by the roiling of
its outer liquid core. Research suggests that at times
this outer core can behave as many magnets instead
of one. These magnets can, in principle, cancel each
other out, causing the magnetic field overall to
weaken or flip.
"We need more data from more sites of the same
reversal to get a better understanding of these
processes," Nowacyzk said.


Source: news.discovery.com/earth/earth-magnetic-field-poles-flip-fast-121024.html