A pole shift is a term used to describe the reversal of the polarity of the Earth’s magnetic field. This means, in present conditions, a compass will start pointing to the south instead of to the north.
According to scientists, in the past 15 million years the Earth’s pole has shifted four times for every one million years. Although based on this finding, a pole shift will occur every 250,000 years, the shifting does not happen at regular intervals. For example, sometime in the Cretaceous period, the Earth’s polarity remained the same for more than 30 million years, although scientists consider this an anomaly. The last recorded pole shift happened 790,000 years ago. This, according to some scientists that a pole shift is due, while others think that it is already slowly happening.
The Earth’s magnetic field is generated deep inside the Earth by various processes. The Earth’s core is made of molten iron and it in turn surrounds an inner core of iron. Each core rotates at different rates. The interaction of the two cores along with other as yet vaguely understood geophysical processes creates a “hydromagnetic dynamo.” The electric field generated is similar to that of a huge bar magnet.
Some scientists believe that a pole shift is already happening because of the decrease in the strength of the magnetic field’s intensity. It has dropped by 10 to 15 percent over the last 150 years and with the rate of decay becoming faster over the last few years. If the present rate of decay continues, the magnetic field will be gone in 1000 to 2000 years.