Flippin’ Earth

The Earth’s magnetic poles might feel like a constant – north is north, south is south – but they turn out to be a lot more complicated than that, as we found out yesterday in our event at the British Science Festival in Aberdeen, where Kathy Whaler, Conall Mac Niocaill and Ciaran Beggan took our audience on a tour of the Earth’s magnetic field and what it does for us.

Our event getting going at the University of Aberdeen

The expeditions which made the south pole famous in the early twentieth century, a race won by Amundson and lost so tragically by Scott, were striving to reach the geographical South pole, rather than the the magnetic pole. And while the geographical poles are more or less (though not entirely) fixed, the magnetic poles are much less predictable.

So what’s the difference? The geographical poles are the two points where the Earth’s axis of rotation intersects its surface. That sounds straightforward enough, but the axis does wobble slightly so its not completely fixed. Magnetic poles are a different story – they’re constantly moving across the surface – making them a lot less reliable for navigation than you might think.

Simulated three-dimensional structure of Earth’s magnetic field

In fact, in the last century magnetic north has migrated more than 1500 km, which sounds like more than just a wobble. Not only that, but the strength of the field has declined by around ten percent in the last 150 years.

That sounds dramatic, but its nothing compared to what the Earth has experienced in the past.

‘From longer term records of the fossil magnetism recorded in rocks, we know that the poles reverse on average every quarter of a million years’ says Conall.

A total reversal of the field – north is south, south is north – sounds like pretty bad news. Even worse news is that the last time this happened was around 780,000 years ago – so it sounds like we’re well overdue another one.

‘There’s no way to tell whether this is the beginning of a reversal or just normal fluctuations’ says Ciaran. ‘We won’t know if we’re in another reversal until it happens.’

No need to panic, disaster movie fans. Although we know it will happen eventually, reversal is a random process, so that 780,000 year time gap is no proof it’s about to happen. And if it is, reversal takes around 3-5 thousand years to complete. So it won’t be even remotely like this:

When it does happen, its hard to know what the effects will be for Earth’s inhabitants, says Ciaran, because we’ve never been around to see it before.

‘The most immediate effects will be to low orbit satellites, which will need to be protected against solar radiation. Large power lines will need to be redesigned. Technology moves very fast, so there’s no reason to think we’ll be caught out.’

In the few thousand years a reversal will take, there will be a period where the field strength is so low it will effectively disappear. Compasses will be useless, and animals which rely on the field to navigate might be in trouble. There could even be ‘multiple poles’ – several north and south poles distributed throughout the planet.

Whatever happens, it will be slow, and we’ll have time to adapt. In fact, we should be thankful for magnetic reversals – they’ve been a key part of the evidence used to reconstruct the Earth’s tectonic history, and provided the vital clue for Fred Vine and Drummond Matthews in their development of plate tectonics in the 1960s.

It was the ‘stripes’ of the differently magnetised oceanic crust, symmetrical on either side of oceanic ridges, that hinted at a spreading of the sea floor from the ridges, and led to one of the most revolutionary theories in the history of Earth science.

So, no exploding mobiles or birds crashing into windows – but for Earth scientists, and for our huge audience yesterday, magnetic reversals still provide plenty of reasons for  excitement.

2 thoughts on “Flippin’ Earth

  1. Pingback: Stuff we linked to on Twitter last week | Highly Allochthonous

  2. This is not a question of whether—only a question of when—yet the public knows practically nothing about the causes and effects of this life-altering event. It is vitally important that people know about this potentially devastating occurrence. The (overdue) reversal of the north and south magnetic poles and the confusion resulting from a complete absence of a magnetic pole or a multiplicity of poles during a transition period will have profound effects on life. Many species depend on the magnetic fields within and above the earth in seeking food or navigating during extensive migrations. Further, GPS and communication satellites will fail or become unreliable. The internal changes in the molten mantle and the direction of its circulation could have an unpredictable effect on the earth’s external magnetosphere and the amount of solar and cosmic radiation reaching its surface. If the magnetic envelope that surrounds our planet is disturbed, the consequences in terms of extenuating external threats such as meteor and asteroid collisions are unknown. Protocols for appropriate international responses are needed for a “reasonably probable” future event.

    We know little about how our Earth’s magnetic fields and poles affect climate except that a pole reversal has always been followed by a cooling period. The earth has an internal magnetic field and an external “magnetosphere.” The latter makes life on Earth possible because it retains our breathable atmosphere and protects us against cosmic radiation of solar origin. Magnetism and gravity are entirely different forces so we should not confuse them. Gravity is the mutual attraction between the relative masses of two bodies. Magnetism is the phenomena exhibited by a magnetic field—independent of any external object—(but it can be induced in specific materials electrically).

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