The cataclysmic pole shift hypothesis is the conjecture that there have been rapid shifts in the relative positions of the modern-day geographic locations of the poles and the axis of rotation of a planet. For the Earth, such a dynamic change could create calamities such as floods and tectonic events. This type of event would occur if the physical poles had been or would be suddenly shifted with respect to the underlying surface over a geologically short time frame. This hypothesis is almost always discussed in the context of Earth, but other bodies in the Solar System may have experienced axial reorientation during their existences.
Among the scientific community, there is no research that indicates a rapid change in the position of the rotational axis. There is evidence of precession and changes in axial tilt, but this change is on much longer time-scales and does not involve relative motion of the spin axis with respect to the planet. However, in what is known as true polar wander, the solid Earth can rotate with respect to a fixed spin axis. Research shows that during the last 200 million years a total true polar wander of some 30° has occurred, but that no super-rapid shifts in the Earth's pole were found during this period. A characteristic rate of true polar wander is 1° per million years or less. Between approximately 790 and 810 million years ago, when the supercontinent Rodinia existed, two geologically-rapid phases of true polar wander may have occurred. In each of these, the Earth rotated ~55°
The geographic poles of the Earth are the points on the surface of the planet that are intersected by the axis of rotation. The pole shift hypothesis describes a change in location of these poles with respect to the underlying surface – a phenomenon distinct from the changes in axial orientation with respect to the plane of the ecliptic that are caused by precession and nutation.
Pole shift hypotheses are not to be confused with plate tectonics, the well-accepted geological theory that the Earth's surface consists of solid plates which shift over a fluid asthenosphere; nor with continental drift, the corollary to plate tectonics which maintains that locations of the continents have moved slowly over the face of the Earth, resulting in the gradual emerging and breakup of continents and oceans over hundreds of millions of years.
Pole shift hypotheses are also not to be confused with geomagnetic reversal, the periodic reversal of the Earth's magnetic field (effectively switching the north and south magnetic poles). Geomagnetic reversal has more acceptance in the scientific community than pole shift hypotheses.
An early mention of a shifting of the Earth's axis can be found in an 1872 article entitled "Chronologie historique des Mexicains" by Charles Étienne Brasseur de Bourbourg, an eccentric expert on Mesoamerican codices who interpreted ancient Mexican myths as evidence for four periods of global cataclysms that had begun around 10,500 B.C.
In 1948, Hugh Auchincloss Brown, an electrical engineer, advanced a hypothesis of catastrophic pole shift. Brown also argued that accumulation of ice at the poles caused recurring tipping of the axis, identifying cycles of approximately seven millennia.
In his controversial 1950 work Worlds in Collision, Immanuel Velikovsky postulated that the planet Venus emerged from Jupiter as a comet. During two proposed near approaches in about 1,450 B.C., he suggested that the direction of the Earth's rotation was changed radically, then reverted to its original direction on the next pass. This disruption supposedly caused earthquakes, tsunamis, and the parting of the Red Sea. Further, he said near misses by Mars between 776 and 687 B. C. also caused the Earth's axis to change back and forth by ten degrees. Velikovsky supported his work with historical records, although his studies were mainly ridiculed by the scientific community.
Charles Hapgood is now perhaps the best remembered early proponent. In his books The Earth's Shifting Crust (1958) (which includes a foreword by Albert Einstein who was writing before the theory of plate tectonics was developed) and Path of the Pole (1970). Hapgood, building on Adhemar's much earlier model,speculated that the ice mass at one or both poles over-accumulates and destabilizes the Earth's rotational balance, causing slippage of all or much of Earth's outer crust around the Earth's core, which retains its axial orientation.
Based on his own research, Hapgood argued that each shift took approximately 5,000 years, followed by 20,000- to 30,000-year periods with no polar movements. Also, in his calculations, the area of movement never covered more than 40 degrees. Hapgood's examples of recent locations for the North Pole include Hudson Bay (60°N, 73°W) , the Atlantic Ocean between Iceland and Norway (72°N, 10°E) and Yukon (63°N, 135°W).
However, in his subsequent work The Path of the Pole, Hapgood conceded Einstein's point that the weight of the polar ice would be insufficient to bring about a polar shift. Instead, Hapgood argued that the forces that caused the shifts in the crust must be located below the surface. He had no satisfactory explanation for how this could occur.
Hapgood wrote to the Canadian librarian, Rand Flem-Ath, encouraging him in his pursuit of scientific evidence to back Hapgood's claims and in his expansion of the hypothesis. Flem-Ath published the results of this work in 1995 in When the Sky Fell co-written with his wife, Rose.
True polar wander, or the motion of the solid Earth with respect to a fixed spin axis that causes the spin axis to lie over a new geographic position, does occur. This is because of changes in mass distribution throughout the Earth that modify its moment of inertia tensor. The Earth consistently readjusts its orientation with respect to its spin axis such that its spin axis is parallel to the axis about which it has its greatest moment of inertia. This readjustment is very slow. In 2001, historical evidence for true polar wander was found in paleomagnetic data from granitic rocks from across North America. The data from these rocks conflict with the hypothesis of a cataclysmic true polar wander event. This evidence indicated that the geographical poles have not deviated by more than about 5° over the last 130 million years. More rapid past possible occurrences of true polar wander have been measured: from 790 to 810 million years ago, true polar wander of approximately 55° occurred twice.
Copyright(c) 2007 - 2020. All rights reserved.
Copyright(c) 2007
- 2020. All rights reserved.