The Unpredictable Magnetic Poles

Of all the earth's peculiarities, one of the most perplexing is the behavior of the magnetic poles.

Even in Columbus' day, it was recognized that magnetic north did not identify with the geographic north pole. Because of this, navigation on the high seas relied primarily on astronomical observations, and nobody knew where the compass was really pointing to, except that it was somewhere vaguely north.

Now it is known that the earth's north magnetic pole lies in the Baffin Islands of Canada, a little north of Northwest Territories. This is nearly 800 miles from the geographic pole. In the southern hemisphere, the magnetic pole lies even further from the geographic pole.

It would seem to the rational observer that the poles should be on exactly opposite sides of the earth, but they aren't. They wander around seemingly independently.

Anyone who uses topographic maps is aware of the fact there are corrections that need to be taken into account when using a magnetic compass. Over the greater part of Alaska, this correction varies from around 20 to 30 degrees--a relatively large amount compared with the rest of the world. In addition, there is a small annual drift. World-wide, this averages about 0.2 degrees per year. Surprisingly, over most of Alaska, the annual correction needed is essentially nil.

Not only do the poles change their position, the magnetic field itself changes in strength. In the early 1800s, the field was about 6 percent greater than it is now. Around 1600 A.D., it was 50 percent greater, but 5,500 years ago it was only about one-half the present value.

But even these eccentricities in the poles' behavior pale in comparison with the flip-flop act which they perform every million years or so. With modern methods, it is possible to determine, within a few percentage points, how many years in the past individual volcanic rock flows solidified. At the same time, it is possible to determine, from the orientation of the minerals within the hardened lava, which magnetic pole represented north at the time, and which represented south.

That's right! They switch--a process called polarity-reversal.

There is no longer any reasonable doubt that within relatively short periods of geologic time--probably less than 10,000 years--the existing magnetic field can reduce to a very small intensity and then reestablish itself with approximately equal intensity in exactly the opposite direction.

How it manages to do this is one of the great mysteries of modern science. It is now believed that the earth has had its present polarity for about the last 700,000 years, although there is evidence to suggest that a few very brief periods of polarity reversal may have occurred within that time.

An obvious question which arises at this point is: "What effect could field reversals have on living creatures?" The rational answer would be: "It shouldn't have any." A human could stand in the strongest magnetic field ever made by man and never feel a tingle (although some recent studies have indicated that bird migration paths may be influenced by the magnetic field).

In 1971, J.D. Hays of Columbia University suggested, in the Geological Society of America Bulletin, three ways in which magnetic field reversals might possibly influence some organisms, possibly leading to extinction. These were: (1) increased cosmic radiation during times of polarity reversal due to loss of the protective magnetic field, (2) a cause-and-effect relationship between reversals and climatic changes, and (3) actual interaction between organisms and the magnetic field.

As it stands now, there are not black-and-white answers to any of these speculations.