Changes in the direction of the Earth’s magnetic field ‘happens ten times faster than previously thought’, mathematical study claims
- Changes in the direction have been up to 10 times larger than those reported
- Rapid changes are associated with the local weakening of the magnetic field
- Earth’s magnetic field is due to the flow of iron 1,740 miles below the surface
Earth’s magnetic field can change 10 times faster than previously thought, according to new research, almost 100 times faster than current changes.
UK scientists have simulated the history of the swirling flow of iron 1,740 miles below the planet’s surface, spanning the last 100,000 years.
Motion of the liquid iron creates the electric currents that power the field, which helps guide navigational systems, shield us from harmful extra terrestrial radiation and hold our atmosphere in place.
In partnership with researchers in California, they’ve demonstrated that these rapid changes are associated with local weakening of the magnetic field.
The magnetic field is constantly changing and satellites provide new means to measure and track its current shifts.
The study by the University of Leeds and University of California at San Diego gives new insight into the swirling flow of iron 2,800 kilometres below the planet’s surface and how it has influenced the movement of the magnetic field during the past 100,000 years
‘We have very incomplete knowledge of our magnetic field prior to 400 years ago,’ said Dr Chris Davies at the University of Leeds’ School of Earth and Environment.
‘Since these rapid changes represent some of the more extreme behaviour of the liquid core they could give important information about the behaviour of Earth’s deep interior.’
Earth’s magnetic field is created by the movement of liquid iron in the Earth’s outer core, some 1,800 miles below our feet.
The iron is super hot (over 5,432 degrees Fahrenheit) and as runny as water meaning it flows very easily.
As the liquid flows, it drags the magnetic field with it – and its corresponding North and South poles.
These magnetic North and South Poles are different from the geographic North and South poles.
The geographic North and South poles are in a fixed position and are diametrically opposite one another.
The magnetic North and South Poles, meanwhile, are constantly moving and over time become misaligned with their geographic equivalents.
Satellites now provide new means to measure and track the shifts of the magnetic poles, but the field existed long before the invention of human-made recording devices.
To capture its evolution back through time, experts had previously analysed sediments, lava flows and human-made artefacts – but these measurements are unreliable.
Scientists at the University of Leeds teamed up with UC San Diego in California to follow a different approach.
The team combined computer simulations of the field generation process with a recently published reconstruction of time variations in Earth’s magnetic field spanning the last 100,000 years.
Changes in the direction of Earth’s magnetic field reached rates that are up to 10 times larger than the fastest currently reported variations of up to one degree per year.
These rapid changes are associated with local weakening of the magnetic field, the research team say.
This means these changes have generally occurred around times when the field has reversed polarity or during what are known as ‘geomagnetic excursions’.
The World Magnetic Map data shows Earth’s magnetic north is moving at 31 miles per year, away from Canada and towards Siberia
This is when the dipole axis – corresponding to field lines that emerge from one magnetic pole and converge at the other – moves far from the locations of the North and South geographic poles.
A reversing magnetic field could lead problems for turtles, birds and the compass
The Earth’s magnetic field regularly flips poles every few hundred thousand years.
The exact impact of this flip isn’t known as it hasn’t happened in 780,000 years, however geologists and astronomers do have some idea.
One of the biggest impacts will be on animals that use the magnetic field for navigation – such as turtles and birds.
North on the compass will also point to Antarctica rather than Canada.
In terms of the impact on human life – the biggest risk depends on how weak the field gets during its transition.
According to a NASA study there’s no evidence it will disappear completely as ‘it never has before’.
However, there is a risk the field will weaken more than usual – it is variable already – during the change.
If it gets too weak more radiation will get to the Earth’s surface and could cause cancers and other issues.
However, as it will happen over a few thousand years humanity will have time to prepare for any weakening magnetic field.
The only other notable impact of a weakening magnetic field would be auroras at lower latitudes.
The clearest example of a geometric excursion in the University of Leeds’ study was a sharp change in the geomagnetic field direction of roughly 2.5 degrees per year 39,000 years ago.
This shift was associated with a locally weak field strength, in a confined spatial region just off the west coast of Central America, and followed the global Laschamp excursion – a short reversal of the Earth’s magnetic field during the end of the Last Glacial Period.
Recent research has found a few times every million years or so Earth’s magnetic field reverses polarity.
It’s been likened to a giant bar magnet inside the planet getting flipped upside down, with molecules in the outer core switching direction, with the magnetic North Pole becoming the magnetic South Pole.
The team’s detailed analysis indicates that the fastest directional changes are associated with movement of reversed flux patches across the surface of the liquid core.
These patches are more prevalent at lower latitudes, suggesting that future searches for rapid changes in direction should focus on these areas.
‘Understanding whether computer simulations of the magnetic field accurately reflect the physical behaviour of the geomagnetic field as inferred from geological records can be very challenging,’ said Professor Catherine Constable, from the Scripps Institution of Oceanography, UC San Diego.
‘But in this case we have been able to show excellent agreement in both the rates of change and general location of the most extreme events across a range of computer simulations.
‘Further study of the evolving dynamics in these simulations offers a useful strategy for documenting how such rapid changes occur and whether they are also found during times of stable magnetic polarity like what we are experiencing today.’
The study has been published in Nature Communications.
The latest World Magnetic Model, which tracks the movement of the Earth’s magnetic field, revealed last year that the magnetic North pole is undertaking geomagnetic excursions of its own.
Last year, a separate team of researchers reported that the Earth’s magnetic North Pole is travelling at a rate of 30 miles per year.
This is the fastest recorded shift of the Earth’s north since the mid-16th century and could cause havoc for aviation and navigation systems, including smartphone apps that use GPS.
The World Magnetic Model has also located ‘caution zones’ on Earth around the magnetic fields where compasses may be prone to errors and send users off course.
HOW DOES A LIQUID IRON CORE CREATE EARTH’S MAGNETIC FIELD?
Our planet’s magnetic field is believed to be generated deep down in the Earth’s core.
Nobody has ever journeyed to the centre of the Earth, but by studying shockwaves from earthquakes, physicists have been able to work out its likely structure.
At the heart of the Earth is a solid inner core, two thirds of the size of the moon, made mainly of iron.
At 5,700°C, this iron is as hot as the Sun’s surface, but the crushing pressure caused by gravity prevents it from becoming liquid.
Surrounding this is the outer core there is a 1,242 mile (2,000 km) thick layer of iron, nickel, and small quantities of other metals.
The metal here is fluid, because of the lower pressure than the inner core.
Differences in temperature, pressure and composition in the outer core cause convection currents in the molten metal as cool, dense matter sinks and warm matter rises.
The ‘Coriolis’ force, caused by the Earth’s spin, also causes swirling whirlpools.
This flow of liquid iron generates electric currents, which in turn create magnetic fields.
Charged metals passing through these fields go on to create electric currents of their own, and so the cycle continues.
This self-sustaining loop is known as the geodynamo.
The spiralling caused by the Coriolis force means the separate magnetic fields are roughly aligned in the same direction, their combined effect adding up to produce one vast magnetic field engulfing the planet.
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