There’s a region of our planet that no human being has ever visited. No one has ever seen this place, yet what happens here affects every one of us every day of our lives. It’s 2,000 miles beneath our feet, the Earth’s molten core.
Here a vast ocean of liquid iron generates an invisible force, the Earth’s magnetic field. It’s what makes our compasses point north. But it does a lot more: it helps to keep the Earth a living planet. Our neighbors, Venus and Mars, have only weak magnetic fields, which means they’re unprotected from the deadly radiation sweeping through the solar system. The Earth, on the other hand, exists within a vast magnetic cocoon, a force-field that for billions of years has sheltered us on our journey through space.
Searing heat, crushing pressure, and a billion trillion tons of molten iron: these are the conditions at the center of the earth. It seems there’s a storm brewing deep within the Earth, a storm that is weakening our vital magnetic shield.
The Earth’s magnetic field has been our protector for millennia, and now, it appears, it’s about to go away. The Earth’s magnet field is getting weaker rapidly.
Is our invisible shield about to disappear? The question is not if that’s going to happen, it’s when that’s going to happen.
About half way to the center of the Earth we reach the true heart of the Earth, the Earth’s core, an immense molten sphere of liquid iron, and that’s where the Earth’s magnetic field is generated.
Recently, scientists have detected a dramatic change in the Earth’s magnetic field. The core’s ability to generate the field seems to be faltering. Today something very strange is going on with the Earth’s magnetic field: its strength is rapidly decreasing.
The magnetic field is created deep in the Earth’s core. It streams out near the South Pole, loops around the planet, and then runs back into the core near the north magnetic pole. This is the Earth’s protective force field. Without it, we’d be in trouble.
It protects us against radiation from space. It’s a little bit like being in a protective pod. The magnetic field of the Earth shields us from space weather and space radiation. Space weather is nasty. The winds that blow through the galaxy are winds of radiation, some of the most harmful from distant exploding stars.
But there is another source which is much nearer, which is our sun. The sun itself is a thermonuclear furnace, and this flings off huge amounts of dangerous material in very large explosions. In some cases, it’s about the same mass as Mount Everest actually coming towards us.
Every few hours the sun ejects billions of tons of electrically charged particles, the solar wind. Often the Earth lies directly in the path of this onslaught, but Earth’s magnetism deflects charged particles. This means that the solar wind is unable to penetrate the Earth’s magnetic shield, and so flows harmlessly around the planet.
The only visible signs of this drama far above our heads are the Northern and Southern Lights, produced when solar particles trapped in the Earth’s magnetic field are dragged through the atmosphere towards the poles.
We’re lucky on the Earth, we have the magnetic field which deflects the particles and protects us. But if we lost the magnetic field, there would be nothing to stop the radiation bathing the whole of the atmosphere, and the effect would be much more dangerous.
If we shut down the magnetic field, then the solar wind has direct access to the atmosphere. Then we have a process which is equivalent to the erosion in the desert. The wind blows and it blows the sand away. In this case, the sands are atmospheric particles. Slowly but surely, the atmospheric gases, which includes water, are carried away and are lost.
The rate of change (of the magnetic field strength) has been higher over the last three hundred years than it has been for any time in the past five thousand. It’s going from a strong field down to a weak field, and it’s doing it very quickly.
Scientists have turned their attention to a chain of volcanic islands in the middle of the Pacific. Here, there’s a record of the earth’s magnetic field that stretches back millions of years, a record, not of gradual decline, but of a series of spectacular magnetic upheavals.
As lava hits the seawater, it chills very, very fast. And a very interesting thing happens. They actually trap in…they record the Earth’s magnetic field.
As they solidify and cool, these volcanic rocks are preserving a record of Earth’s magnetic field. But the volcanoes of Hawaii have been erupting, on and off, for millions of years, building up the islands. Every layer of lava contains a record of the magnetic field at the time of that eruption. So the Hawaiian archipelago is a hidden chronicle of the Earth’s magnetism stretching back five and a half million years.
That record shows there have been many fluctuations in the field’s strength, but it contains something else of great significance. When lava cools, they record not only how strong the field is, but also in what direction it is pointing.
Today the Earth’s magnetic field runs from south to north—which is why compass needles point towards the North Pole.
When we go back about 780,000 years we find an incredible phenomenon. Suddenly the rocks are magnetized backwards. Instead of them being magnetized to the north like today’s field, they are magnetized to the south. The bizarre implication was that at some point the entire global magnetic field had done a sudden 180-degree flip, completely reversing direction.
And as they examined samples from older and older lava, scientists found more and more reversals—on average, one every 200,000 years.
That the Earth’s magnetic field reverses is an extraordinary phenomenon, but this reversal process is apparently quite common. The last reversal was 780,000 years ago. Before that, there was one about 200,000, before that, again, actually less than 200, so in a sense we are a bit overdue for a reversal.
So is this why the field is getting weaker today? Could it be getting ready to flip?
What’s interesting is whenever it has reversed its polarity, its direction, that happened when the magnetic intensity was very weak. So it was decreasing and decreasing and finally when the dipole part of the field was very weak, then the field reversed.
This is the evidence that what we are seeing today, a loss of field strength, which is indeed linked to the onset of reversals.
We are seeing the emergence of a new patch of reverse flux, a region where the field lines, instead of coming out of the core, are looping back into the core. And that patch then drifts towards the west, hooking up with this other patch of reverse flux to create a large region of what we call the “South Atlantic anomaly,” where the field is about 30 percent weaker. And that patch has grown substantially during the last hundred years in particular. So one question is, “Is the Earth’s magnetic field about to flip?”
In a region of the core 2,000 miles beneath the South Atlantic, the magnetic currents have reversed direction, canceling out the main field, causing its strength to decline. If things continue like this, then we could experience a magnetic phenomenon the Earth has not seen for 780,000 years, a complete flip of the entire global field.
We could be in for magnetic chaos, with magnetic north changing from day to day. More seriously, for perhaps thousands of years, the Earth’s magnetic shield will be weakened, something that will affect every person on the planet.
The intensity of the magnetic field will be weaker, maybe ten, maybe a hundred times weaker than it is today, which means that more cosmic radiation will get through.
This basically opens our defenses so that solar and galactic radiation can hit the atmosphere directly. And this means that the radiation at ground level increases as well.
The structure of the magnetic field won’t be the nice, smooth, simple dipole structure that we have today, which tends to deflect charged particles—cosmic radiation—to the poles of the Earth. Instead there will be several poles all around the Earth, maybe close to the equator. And so, not only will the field be weaker, the field will tend to focus cosmic radiation at low latitudes where most people live.
Some of the information has been collected from NOVA / PBS.org
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