Cos­mic Flip-out

SLOW Magazine - - Contents - Text: Gary Muir Image ©

Ac­cord­ing to sci­en­tists, the Earth’s mag­netic field is mov­ing to­wards a re­ver­sal – a ge­o­log­i­cal phe­nom­e­non which, while it may sound cat­a­clysmic, has hap­pened many times be­fore. In fact, Earth’s ge­o­logic record shows that hun­dreds of pole re­ver­sals have taken place through­out the planet’s his­tory.

Al­though com­plete re­ver­sals have been some­what ir­reg­u­lar, sci­en­tists be­lieve they have hap­pened ev­ery 200,000 to 300,000 years. That is, ex­cept the most re­cent one, which oc­curred 780,000 years ago, dur­ing the Stone Age. The ev­i­dence that ex­ists today sug­gests that Earth might now be in the early stages of a pole re­ver­sal. It is not, how­ever, any­thing we will ex­pe­ri­ence in our life­times or even which our great­grand­chil­dren may ex­pe­ri­ence, as it is an in­cred­i­bly slow process, tak­ing between 1,000 and 10,000 years to com­plete.

Ac­cord­ing to sci­en­tists, the strength of Earth’s mag­netic field has been de­creas­ing at what they call an “alarm­ing rate” for at least the last 160 years – hence their the­ory that we are cur­rently head­ing to­wards a re­ver­sal. Satel­lite data gath­ered by the Euro­pean Space Agency (ESA) shows that Earth’s mag­netic shield is weak­en­ing 10 times faster than pre­vi­ously thought, at 5 % per decade. This is hap­pen­ing pri­mar­ily over South Amer­ica, in an area which sci­en­tists have dubbed the South At­lantic Anom­aly (SAA), and which stretches across the At­lantic Ocean from Chile to South Africa. Since this re­gion was first dis­cov­ered in 1958, its girth has been steadily in­creas­ing, part of an over­all weak­en­ing of the en­tire mag­netic field. In­deed, satel­lites fly­ing over this area fre­quently have their cir­cuits fried by lo­calised ra­di­a­tion spikes.

A weak­en­ing mag­netic field does not have to mean the poles are about to re­verse. Some­times, the field re­cov­ers its orig­i­nal struc­ture, a wan­ing-re­cov­er­ing event known as a ge­o­mag­netic ex­cur­sion. Re­searchers from the Uni­ver­si­ties of Liver­pool and Ice­land, and the GFZ Ger­man Re­search Cen­tre for Geo­sciences, have been looking into this and study­ing past ex­cur­sions. They ar­gue that there are two pe­ri­ods in his­tory – 49,000 and 46,000 years ago re­spec­tively – where anom­alies like the SAA (but stronger) oc­curred, nei­ther of which caused a pole re­ver­sal.

The Earth’s core is made up of molten iron which, as it flows, pro­duces an elec­tri­cal cur­rent, which in turn cre­ates the Earth’s mag­netic field. It is by way of this mag­netic field that we can nav­i­gate. When a com­pass nee­dle points north, it is in fact point­ing to Earth’s mag­netic south. This is be­cause mag­netic op­po­sites at­tract. Sci­en­tists’ ex­pla­na­tion of ex­actly how the pole re­ver­sal hap­pens is simple enough: Patches of iron atoms in Earth’s liq­uid outer core be­come re­verse-aligned, like lit­tle mag­nets ori­ented in the op­po­site di­rec­tion to those around them. When these re­versed patches in­crease in size to the ex­tent that they dom­i­nate the rest of the core, the over­all mag­netic field flips.

The Earth’s last com­plete pole re­ver­sal was named the Brun­hes-matuyama re­ver­sal, and it hap­pened at a time when plant and an­i­mal life on the planet was flour­ish­ing. Fos­sils dat­ing to this pe­riod have led geo­physi­cists to be­lieve that the poles switch­ing had no cat­a­strophic im­pact on life. This be­lief is sup­ported by glacial records, which in­di­cate that the re­ver­sal did not cause a ro­ta­tion or shift in the Earth’s axis – an oc­cur­rence which would have dras­ti­cally al­tered the planet’s cli­mate.

While the ef­fects of the afore­men­tioned po­lar flip seem to have been min­i­mal, sci­en­tists can­not say for cer­tain what a pole re­ver­sal would mean today. What they are sure of is that, while Earth’s mag­netic field will not dis­ap­pear en­tirely, it could weaken dras­ti­cally. This would al­ter the func­tion­al­ity of tech­no­log­i­cal de­vices, satel­lites and power grids, and give those in the avi­a­tion in­dus­try some se­ri­ous new chal­lenges. Another cause for con­cern could be the ef­fect on Earth’s fauna. Many an­i­mal species have mag­neto re­cep­tion, which they use to nav­i­gate, such as when they mi­grate. A weak­ened field would dis­ori­ent those species which rely on ge­o­mag­netism for nav­i­ga­tion, such as bees, pi­geons, salmon, tur­tles, whales, and even cer­tain bac­te­ria.

Where a po­lar re­ver­sal will prob­a­bly have the great­est im­pact, sci­en­tists say, con­cerns ra­di­a­tion. This is be­cause a strong mag­netic field works to pro­tect Earth from the sun’s ra­di­a­tion blasts, and thus a weak­ened mag­netic field could lead to the for­ma­tion of “ozone holes”. Of­fi­cials at NASA pre­dict that the re­sul­tant in­crease in so­lar ra­di­a­tion would be small, and luck­ily not deadly.

As to whether a flip will cause a shift in the con­ti­nents, or nat­u­ral dis­as­ters like earth­quakes, sci­en­tists say that it’s not likely. Changes in the Earth’s liq­uid core hap­pen on a dif­fer­ent dis­tance and timescale to con­vec­tion in the planet’s mantle – the process that causes Earth’s tec­tonic plates to shift. While the liq­uid core does come into con­tact with the bot­tom of the mantle, sci­en­tists say it would take tens of mil­lions of years for changes in the core to work their way through the mantle and in­flu­ence the mo­tion of the tec­tonic plates.

Ul­ti­mately, Earth is too com­plex a sys­tem for sci­en­tists to know with cer­tainty which out­come to ex­pect – a re­ver­sal or a ge­o­mag­netic ex­cur­sion. If the re­ver­sal should hap­pen, at least Earth’s in­hab­i­tants will have plenty of time – a few thou­sand years, in fact – to ad­just to the changes.

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