by Peter P. Much talk has revolved around coming pole shifts on Earth, either physical or magnetic. Does the evidence bear out such an event happening?
An 180-degree physical inversion of the planets's solid crust around the molten core would be the ultimate cataclysmic "Earth change". However, more than a few experts find this scenario most likely only if another
planetary body - such as a 'rogue planet' or similar cosmic anomaly - passed in close proximity to the Earth, providing enough torque for such an event to occur.
A reversal of the magnetic poles is much more likely, however, as it's happened before. Seen in the paleomagnetic record, locked into rocks of the ocean floor and in some lava flows, scientists think the time between reversals on the Earth falls somewhere between every 100,000 to 25 million years, with the reversal itself taking about 5,000 years. 
Not that just the reversal takes that long, mind you, and therein lies the crux of the problem. No, during much of that time, the geomagnetic field strength decreases - which counts as part of the 'reversal' process. According to laboratory analysis of thermorenanent magnetization carried by clay baked in ancient times, the average global field intensity in any given region went through a broad maximum about 2,000 years ago.  After reaching a maximum, it then began its long descent.
NASA's Magnetic Field Satellite concurs, confirming a trend that goes back to at least 1830; namely, that the terrestrial magnetic field is decreasing in strength. At a rate measured by the satellite, the Earth's field will hit 'zero' in about 1,200 years.  That, at least, is the estimate.
One contributing factor to the decrease, and eventual reversal, may be intensifying core spots within the inner core that are magnetized in a sense opposite of the main field ; while competing energy sources, such as heat loss at the mantle-core boundary (itself possibly contributing to climate change) and growth of the inner core may also be contributing factors. 
As the field reaches 'zero', or close to it (some estimate the magnetic field will be at 20% of normal during a reversal), complete with periods of rapid and radical changes , something much more threatening than the upcoming reversal will occur.
First, as the field weakens, so does what many
believe is the natural navigatory force for many living creatures. Studies have shown that
whales, dolphins, birds and even mollusks and mice use the geomagnetic field as a guiding
device. Some, like mice, use it as a directional guide ; while cetaceans use the total
geomagnetic field as a map, not for directional information, as we would use a compass,
but by navigating the contours of magnetic "hills and valleys" in a field that
is anything but uniform. 
Peter P. is a Phoenix-based freelance writer who has split his work life during the past ten years between journalism (both as a freelancer & on staff of a biweekly alternative paper) and assisting the developmentally disabled. He is currently tracking 1998 predictions, which is part of the reason for 'Earth-Changes Weekly'. Subscription to the list is free, and there are various methods of interacting with it. For further information contact: firstname.lastname@example.org
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