Thesis and Introduction:
Though there is little scientific or academic disagreement as to the reality of the existence of geomagnetic polar shifts and reversals, there is much speculation and theorizing as to what the hypothetical impacts and effects of such an event would be; and still more controversial is just how hypothetical such an eventuality actually is.
The magnetic field waxes and wanes, poles drift and, occasionally, they flip. Every so often, our planet’s magnetic poles reverse polarity. J.A. Jacobs of the Institute of Earth Studies at the University of Wales writes: “Apart from it spatial variation, the earth’s magnetic field also shows temporal changes: secular changes on a timescale of hundreds of years, and, on an even longer timescale, to complete reversals of polarity.” 
Reversals happen on average once every 250,00 years, and they take hundreds if not thousands of years. Each published polarity transition reported a slightly different duration, from just less than 1,000 years to 28,000 years.  Earth’s magnetic field reverses every few thousand years at low latitudes, a geologist funded by the National Science Foundation (NSF) has concluded.  Reversals take a few thousand years to complete, and during that time—contrary to popular belief—the magnetic field does not vanish. 
According to S.S. Tsygankov and E.I. Shemyakin and F. Stasey of the Institute of Geosphere Dynamics at the Russian Academy of Sciences in Moscow: “The phenomenon of Geomagnetic Field Inversion (GFI) is one among the eight most important problems in paleomagnetology.” 
How It Works:
It was not until 1600 that the true nature of the magnetic field was revealed by the experiment work of Royal College of Physicians of London President William Gilberd, whose famous treatise "De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure" ("On the Magnet and Magnetic Bodies, and on That Great Magnet the Earth") has been described as the first modern scientific work. Gilbert found that the variation in direction of magnetic force and the distribution of magnetic dip was in agreement with what was then known about the Earth’s magnetic field. Gilbert concluded that the Earth behaved as a large magnet, its magnetic field being due to causes within the Earth, and not from any external agency, as was supposed at that time. 
However, we still don’t know for certain how the Earth’s magnetic field is generated and maintained. The origin of the magnetic field and its reversals is one of the oldest problems in physics, and one of the most active areas of research in geophysics today. 
Scientists believe Earth’s magnetic field is generated deep within our planet. “To understand what is happening;” Says American Geophysical Union Fellow and University of California Santa Cruz Earth and Planetary Sciences Department Professor Gary A. Glatzmaier; “We have to take a trip…to the center of the Earth where the magnetic field is produced.”  
Roughly speaking, Earth is like a chocolate-covered cherry—layered, with liquid beneath the surface and a solid inner core. 
Beneath the planet’s relatively thin crust is a thick solid layer called the mantle. At the heart of our planet lies a solid iron ball 70% as wide as the moon and about as hot as the surface of the sun. Researchers call it the inner core. The inner core has its own ocean: a very deep layer of liquid, believed to be composed of swirling convection flows of molten iron and nickel, known as the outer core. The Earth’s magnetic field is understood to come from this ocean of iron, which is an electrically conducting fluid in constant motion. 
The Earth’s magnetic field is created deep within our planet’s outer core through what is known as the geodynamo. There, the heat of the Earth’s hot solid inner core churns the liquid outer core sitting atop it like water on a hot stove. These complex motions generate our planet’s magnetism through a process called the dynamo effect. The churning acts like convection, which generates electric currents and, as a result, a magnetic field. 
This idea that turbulent activity at the outer core of the planet generates its magnetic field currently dominates scientific thinking. 
Our planet’s magnetic field varies with time, indicating it is not a static or fixed feature. Instead, some active process works to maintain the field. “The typical lifetime of a magnetic field like the Earth’s;” Says Glatzmaier; “Is several tens of thousands of years. The fact that it’s existed for billions of years means something must be regenerating it all the time.” That process is most likely a kind of dynamic action in which the flowing liquid material in the outer core generates the magnetic field, geologists believe. 
Most scientists believe Earth’s magnetic field is sustained by a complex self-sustaining interaction known as the “geomagnetic dynamo”. The term describes the theoretical phenomenon believed to generate and maintain Earth’s magnetic field. According to general accepted theory—the dynamo theory—interactions between the churning convecting flow of molten iron in the Earth’s outer core and the magnetic field generate electrical current that, in turn, creates new magnetic energy that sustains the field.  “It’s a very complicated chaotic system, and it has a life of its own.” Glatzmaier said.  
However, there is no way to peer 4,000 miles (6,400 kilometers) into Earth’s center to observe the process in action. 
It is known, however, that the mechanism of magnetic field generation is related to Earth’s rotation.  The rotation of planets may be among the necessary conditions for the formation of their magnetic fields. However, rotation alone is insufficient for the creation of a planetary magnetic field. 
The inner core spins at its own rate, as much as 0.2 degrees of longitude per year faster than the Earth above it;  and there is also stormy activity deep in the Earth’s molten outer core, such as “hurricanes”—whirlpools powered by the Coriolis forces of the Earth’s rotation. 
Process And Effects:
Figuring out what happens as the field reverses polarity is difficult because reversals are rapid events, at least on geologic time scales. It is generally accepted that during a reversal during a reversal, the geomagnetic field decreases to about 10 percent of its full polarity value. After the field has weakened, the directions undergo a nearly 180-degree change. Magnetic North heads South, and—over about 1,000 years—the field does a complete flip-flop, and the field strengthens in the opposite polarity direction.   A major uncertainty, however, has remained regarding how long this process takes. “Although this is usually the first question people ask about reversals.” Says Woods Hole Oceanographic Institution Postdoctoral Scholar, Geological Society of America Elected Fellow, U.S. Geological Survey Research Geophysicist, Massachusetts Institute of Technology Earth, Atmospheric, and Planetary Sciences Department Visiting Scientist and Georgia Institute of Technology Associate Professor of Geophysics Carolyn Ruppel. 
Scientists have been observing changes in the direction of Earth’s magnetic which took place recently as well as in the distant past.  The study of Earth’s past magnetism is called paleomagnetism.
The magnetic field has exhibited frequent but dramatic variation at irregular times in the geologic past: It has completely changed direction. Jacobs writes: “Secular changes can take place even on a time scale of 10-20 years, and appear to be regional rather than planetary phenomenon. Such changes cannot be extrapolated accurately over intervals longer than 4 or 5 years.” 
The geological record confirms that magnetic field reversals have occurred in the past. Earth’s magnetic field has flipped many times over the last billion years, according to the geologic record. “We can see the reversals in the rocks, but they don’t tell us how it happens.” Says Glatzmaier. These records make it possible to determine the major features of reversals, he said. “Some reversals occurred within a few 10,000 years of each other;” He says; “And there are other periods where no reversals occurred for tens of millions of years.” 
Rocks in an ancient lava flow in Oregon suggest a brief erratic span 16 million years ago magnetic North shifted as much as 6 degrees per day. After a little more than a week, a compass needle would have pointed toward Mexico City. 
Although the Oregon data is controversial, Earth scientists agree that the geological evidence as a whole—the “paleomagnetic” record—proves such reversals happened many times over the past billion years.  
Jacobs writes: “considerable changes over 104 years may be determined from archaeomagnetic and paleomagnetic studies.” 
Since the time of Albert Einstein, researchers have tried to nail down a firm timeframe during which reversals of Earth’s magnetic field occur.
Extrapolated Predictions Future Reversals:
Once could only perhaps take comfort in the knowledge that these reversals happen infrequently—on average every 250,000 years—according to the geologic record of Earth’s polarity, but maybe not when one considers that the last time Earth’s magnetic field flipped was over 780,000 years ago, and, since more than double the time interval has elapsed since the last reversal, compared to the time lapse between the previous two reversals, some believe we may be overdue for the next North-South flip, and the next one may be currently underway. 
International Union of Geodesy and Geophysics International Association of Geomagnetism and Aeronomy Commission on Geophysical Risk and Sustainability Member and Geomagnetic Observatories, Surveys and Analyses Data and Models Division Chair, American Geophysical Union Member, and Natural Environment Research Council British Geological Survey Earth Hazards and Systems Geomagnetism Team Head Alan W P Thomson writes: “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.” 
Royal Society of London for Improving Natural Knowledge Fellow Sir James Clark Ross located the North Magnetic Pole for the first time on June 1, 1831 on the Boothia Peninsula in the far north of Canada, after an exhausting journey during which his ship got stuck in the ice for four years. In 1904, Roald Engelbregt Gravning Amundsen found the pole again and discovered that it had moved—at least 50 km since the days of Ross. 
It is not only the direction but also the strength of the magnetic field that is a concern. Earth’s magnetic field—the force the protects us from deadly radiation bursts from outer space—is weakening dramatically.  While nobody quite knows why this is occurring, the weakening of Earth’s magnetism is believed by many of the most respected scientists in the field of geomagnetism to be one of the factors predictive of a pole realignment, a precursor, and perhaps even a forecaster, of magnetic polar reversal sometime in the near future. 
In the time of the dinosaurs, at an estimated 2.5 gauss, it was eighty percent stronger than it is now. 
Today the field is about 10 percent weaker than it was when Royal Swedish Academy of Sciences foreign member and Royal Observatory Göttingen Director and Göttingen University Observatory Astronomy Professor Johann Carl Friedrich Gauss first measured it in 1845. For more than 100 years, scientists have noted the strength of Earth’s magnetic field has been declining, but have disagreed about interpretations.  In the past century, there has been further decline of Earth’s magnetic field by another five percent down to only .5 gauss.  Gauthier Hulot of the Paris Institute of Earth Physics has discovered that Earth’s magnetic field seems to be disappearing most alarmingly near the poles, a clear sign that flip may soon take place. 
But according to Glatzmaier, even the weakening currently underway may be a false alarm. The ongoing 10% decline doesn’t mean that a reversal is imminent. “The field is increasing and decreasing all the time.” He says. “The field often gets weak, then bounces back, never having flipped. We know this from the paleomagnetic record.”  
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