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True Polar Wander

Let us now praise crazy men

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Recently some highly respected earth scientists went out on a limb. In the 25 July 1997 issue of Science, a team of researchers led by Joseph Kirschvink asserted that about 550 million years ago, the whole Earth slewed halfway around, putting its polar lands down at the equator, over a rather brief period—15 million years. That doesn't sound brief, but for something this profound it's pretty darn fast. (Here's a PDF of the paper.) For me, the whole thing was a bit of déjà vu, a reappearance of the alluring notion of "true polar wander."

How Poles Wander

In the decades before plate tectonics was accepted, the orientation of the ancient magnetic field was a severe puzzle. A grain of magnetite (or any other magnetic mineral) naturally tends to point toward the poles, like a miniature compass needle. Either it turns that way while it is in soft sediments before they become rock, or it forms in a body of lava and has the prevailing magnetic field stamped into it the minute it cools enough to hold a magnetic "charge."

But in rocks all over the world of all different ages, these micro-magnets point in many different directions. Either (1) the rocks got tipped or bent, or (2) the continents they sit in moved, changing their various orientations with respect to the poles ("polar wander" for short), or (3) the whole Earth shifted with respect to the poles ("true polar wander")—or, of course, some bewildering combination of all three. For some 50 years, specialists have been sorting out the first factor, then the second, to see if the third one enters the picture at all.

The pile of magnetic data has been untangled into an intricate tale of ordinary polar wander that we know today as plate-tectonic motions. But in the 1950s the early workers considered the idea of true polar wander, then set it aside. It wasn't demanded by the evidence, and pretty soon people were too busy with the details to talk about grand motions. Besides, true polar wander had a bad aura clinging to it.

Polar Wander, an Outsider Idea

In making its way toward truth, science depends on a delicate mixture of method and madness, of care and creativity. Vision is unreliable, but there are times when you have to use it. The years before plate tectonics was accepted were one such time, and lots of people called upon this particular crazy idea. Some were respected insiders, but outsiders had been there first:

  • Emmanuel Velikovsky, whose dizzying tales of careening planets had Earth being knocked off its axis in every other episode, gained a disturbing degree of popularity.
  • Alfred Wegener was a less virulent example, being a meteorologist whose unsophisticated theory treated the solid Earth like the fluid atmosphere, but he had been largely considered discredited since his heyday in the 1920s.
  • Charles Hapgood, a tenured historian of science, invoked the mechanism in his 1953 book Earth's Shifting Crust, notable mainly for its preface by the old and vulnerable Albert Einstein. (Hapgood is not forgotten—visit this site for a glimpse of that brand of craziness.)

Responsible Polar Wander

Keith Runcorn was one of the insiders. His early work showed that the evidence favored continental, not global drift, but he continued to think about true polar wander after it left the cutting edge. I heard him present talks in his later years that used it to explain the gross architecture of the Moon and Mars.

The late Warren Carey of the University of Tasmania, too, was a freewheeling thinker who invoked large-scale reorientation of the Earth for many years. It was a key part of his expanding-Earth theory (which he staunchly supported to the end), one of the craziest theories ever to be taken seriously. But Carey and Runcorn never lost the respect of their colleagues.

Still, the subject of true polar wander has been off the table for decades and out of the major journals. Its dramatic reappearance in 1997 may succeed in bringing it back to Earth from its exile on other worlds. Perhaps Kirschvink can tip Earth—and Earth science—off its axis for good. This is not his only big-screen idea: he has published on the panspermia hypothesis, on earthquake prediction from animal behavior, a grand unified theory of biomineralization, and Snowball Earth. Surely that makes him a crazy man in the best scientific sense.

PS: There ought to be crazy women in geology, but only in the last 50 years or so have there been many at all. (Read about some in the Famous Women in Earth Science list.) For most of the 1900s, women were routinely steered toward microfossil studies, and an unsung army of women built the enormous microfossil database that is still the gold standard of rock dating (one of them, Helen Tappan Loeblich, won the Moore Medal in 1984). Full equality will not come until women feel as free as men to spin wild theories without destroying their careers.

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