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OU on the BBC: Background Brief - Magnetic Mayhem: The Story So Far

Updated Tuesday, 8th August 2006
The background to the risks of the planet swapping its polarity - magnetic reversal

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Compass The Millennium Bug may have turned out to be small potatoes in terms of things to worry about - but if you’re missing that sense of potential calamity in your life, get your head around Magnetic Reversal...

By Magnetic Reversal, scientists mean that the Earth’s axis could flip direction.

North would, literally, become South.

As well as confounding our compasses, this would mean the total collapse of the world’s telecommunications - and possible mass extinctions of the planet’s animal and plant life ...

That might sound like a strictly sci-fi scenario, but unfortunately it’s not. Janice Acquah set off to find out more...

Ship's log Detailed shipping logs going back to the 16th century show that even in the past few centuries, magnetic north has moved around somewhat - as much as 30 degrees at the extremes.
But we need to go back much further for evidence that the Earth’s magnetic poles have reversed in the past ...

Fortunately, that’s exactly what geologist Dr Ellen Plaxman is working on at University College London. She specialises in "palaeomagnetism" - in other words, she studies what the Earth’s magnetic fields have been up to throughout the planet’s lifetime.

Dr Ellen Plaxman with chainsaw (She also enjoys playing with chainsaws - which she insists are essential to her work... but more about that later!)





Motorway The reason the Earth has a magnetic core is that its centre is made of liquid iron. This iron core conducts electricity and generates an electric current (just like an alternator in a car) - and this creates a North-South magnetic field.
When rocks are formed on the earth’s surface, any magnetic minerals within them - like iron - align themselves with the planet’s North-South axis. So ever after, those rocks hold the imprint of exactly how the magnetic axis lay at the time they solidified.
Which is where the chainsaws come in. Because by analysing rock samples from around the world, geologists such as Dr Plaxman are able to determine which direction the earth’s magnetic field was facing at the time the rock was formed - over millions of years.

And the evidence is conclusive: some rocks are magnetised in exactly the opposite direction to what we’d expect today. The Earth has clearly flipped its magnetic lid many times already... and it could happen again.

Compass "We have a very good record," Dr Plaxman says, "from back to 200m years ago, when the oldest ocean crust was formed.

"Recently we’ve had three reversals per million years, and there’s some evidence we could be going into another phase of reversal..."

Dr Bob Spicer with fossil The reason geologists think we could be approaching a magnetic reversal is that the intensity of the earth’s main magnetic field is currently decreasing. And geologists know that this does always happen before a reversal occurs...

But what would happen if there was one in the near future?

A few examples ...

- Firstly, if the magnetic field disappears (on its way to reversing) we’ll have no shield against the magnetic particles in the solar wind. Computer systems could be vulnerable to this kind of magnetic radiation, and life might be too. But could it bring about mass extinctions of animals and plants? Hopefully not, geologists say there is no evidence that this has happened before, despite many reversals occurring in the past.

- Characteristics of the earth’s atmosphere such as the Northern Lights and the Ozone hole would move along with the N-S axis.

- A reversal would also make all radio communications more difficult.

- Bacteria and single-celled organisms that use the earth’s magnetic alignment to orientate themselves have suffered in the past and this might happen again...

So how worried should we be? Well, it’s definitely going to happen, but nobody’s totally sure when. Some experts say it’s likely to be in 1000-1500 years time. By which time, we may have the technology not only to predict exactly what the negative effects will be, but to counteract them as far as possible.

Til then, if you’re a compulsive worrier about natural catastrophes, you might want to focus your thoughts on rogue earthbound asteroids instead! Can we avoid Impact Planet Earth?

First broadcast: Friday 15 Oct 1999 on BBC TWO


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