Earths magnetic field

The strength of the Earth's magnetic field has decreased 10 percent over the past 150 years, raising the remote possibility that it may collapse and later reverse, flipping the planet's poles for the first time in nearly a million years.

At the current rate of decline, the field could vanish altogether in 1,500 to 2,000 years. Hundreds of years could pass before a flip-flopped field returned to where it was 780,000 years ago.

However scientists cautioned that scenario is an unlikely one.

Instead, the weakening, measured since 1845, could represent little more than an "excursion," or lull, in the naturally variable strength of the Earth's magnetic field.

Such a lull can last for hundreds of years, however, and still have significant effects, especially in regions of the Earth where the weakening is most pronounced.

Over the southern Atlantic Ocean, a continued weakening in the strength of the magnetic field has diminished the shielding effect it has locally in protecting the Earth from the natural radiation that bombards our planet from space.

As a result, satellites in low-Earth orbit are left vulnerable to that radiation as they pass over the region, known as the South Atlantic anomaly.

Among the satellites that have fallen prey to the harmful effects was a Danish satellite designed, ironically, to measure the Earth's magnetic field.

The weakening, if coupled with a subsequently large influx of radiation in the form of protons streaming from the sun, can also affect the chemistry of the atmosphere.

That can lead to significant but temporary losses of atmospheric ozone.

Earth's magnetic field - the force that protects us from deadly

 radiation bursts from outer space - is weakening dramatically.

Scientists have discovered that its strength has dropped precipitously over the past two centuries and could disappear over the next 1,000 years.

The effects could be catastrophic. Powerful radiation bursts, which normally never touch the atmosphere, would heat up its upper layers, triggering climatic disruption. Navigation and communication satellites, Earth's eyes and ears, would be destroyed and migrating animals left unable to navigate.

Earth's magnetic field has disappeared many times before - as a prelude to our magnetic poles flipping over, when north becomes south and vice versa.

Reversals happen every 250,000 years or so, and as there has not been one for almost a million years, we are due one soon.

For more than 100 years, scientists have noted the strength of Earth's magnetic field has been declining, but have disagreed about interpretations. Some said its drop was a precursor to reversal, others argued it merely indicated some temporary variation in field strength has been occurring.

But now Gauthier Hulot of the Paris Geophysical Institute has discovered Earth's magnetic field seems to be disappearing most alarmingly near the poles, a clear sign that a flip may soon take place.

Using satellite measurements of field variations over the past 20 years, Hulot plotted the currents of molten iron that generate Earth's magnetism deep underground and spotted huge whorls near the poles.

Hulot believes these vortices rotate in a direction that reinforces a reverse magnetic field, and as they grow and proliferate these eddies will weaken the dominant field: the first steps toward a new polarity

And as Scientific American reports this interpretation has now been backed up by computer simulation studies.

How long a reversal might last is a matter of scientific controversy, however. Records of past events, embedded in iron minerals in ancient lava beds, show some can last for thousands of years - during which time the planet will have been exposed to batterings from solar radiation. On the other hand, other researchers say some flips may have lasted only a few weeks.

Exactly what will happen when Earth's magnetic field disappears prior to its re-emergence in a reversed orientation is also difficult to assess. Compasses would point to the wrong pole - a minor inconvenience. More importantly, low-orbiting satellites would be exposed to electromagnetic batterings, wrecking them.

In addition, many species of migrating animals and birds - from swallows to wildebeests - rely on innate abilities to track Earth's magnetic field. Their fates are impossible to gauge.

As to humans, our greatest risk would come from intense solar radiation bursts. Normally these are contained by the planet's magnetic field in space. However, if it disappears, particle storms will start to batter the atmosphere.

These solar particles can have profound effects. On Mars, when its magnetic field failed permanently billions of years ago, it led to its atmosphere being boiled off. On Earth, it will heat up the upper atmosphere and send ripples round the world with enormous, unpredictable effects on the climate.

It is unlikely that humans could do much. Burrowing thousands of miles into solid rock to set things right would stretch the technological prowess of our descendants to bursting point, though such limitations do not worry film scriptwriters. Paramount's sci-fi thriller, The Core - directed by Englishman Jon Amiel, and starring Hilary Swank and Aaron Eckhart - depicts a world beset by just such a polar reversal, with radiation sweeping the planet.

The solution, according to the film, involves scientists drilling into Earth's mantle to set off a nuclear blast that will halt the reversal.

Given that temperatures at such depths rival those of the Sun's surface, such a task would seem impossible - except, of course, in Hollywood.

What Exactly is a Reversal?

A polar reversal is when the normal magnetic polarity that we have now changes. During a reversal, the planet will experience a rapid shift in the position of the poles relative to each other. Recent discoveries have lead scientists to believe that the magnetic field may not go away, but it will become tangled with in itself. This entanglement may or may not increase the amount of radiation that we are exposed to, due to the secondary protection we receive from the atmosphere. For the poles to be disturbed in the way that is said, the geodynamo would have to be disrupted. This means that the convection current occurring in the inner and outer cores would have to be tampered with. The exact cause of this have not been determined.

Magnetosphere

The earth's core contains a multitude of magnetic compounds including iron, cobalt, and nickle. These compunds, in conjunction with the outer core, produce a magnetic field. The process is called geodynamo, and is described as losely as the process by which the inner core and outer core form a convection current which in turn produces a magnatic field. The field extends out many miles past the earth's surface, and deflects the harmful radiation emitted from the sun. During solar flares and other events of intense radiation emmission the field is still able to protect us. The sun itself has extreme fluctuations in the amount to radiation that is emitted, and the magnetosphere protects us from these rays. If the magnetosphere were to weaken at any point, the repercussions could be devestating in the long run.