Pole shift refers to a geological phenomena in which the Earth's outermost layers move together as one piece.

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Some say the world will end in fire; some say ice. Lately, screenwriters and apocalypse enthusiasts have preferred natural cataclysms as their world-killers. As for when the end will arrive, those folks who claim to be in the know have an affinity for stamping 2012 as the Earth's sell-by date.

Why 2012? The answer traces back to true believers' interpretations (and reinterpretations) of Nostradamus, Edgar Cayce and various other ambiguous and nonscientific sources. Some armchair eschatologists have narrowed the expiration date further, to Dec. 21, 2012 -- when, they argue, the Mayan Long Count calendar ends its 5,125-year cycle. However, experts agree that the Mayans themselves did not believe that the world would end on this date, so feel free to buy green bananas on Dec. 19, 2012 [source: MacDonald].

The lack of scientific evidence for the coming apocalypse hasn't deterred believers from trotting out scientific theories to serve as evidence of imminent mass destruction. One of the most remarkable ideas they've chosen to flog is the pole shift hypothesis, in which the Earth's crust and mantle (or outermost layers) move as one piece. Pole shift might send the poles sliding toward the equator, swing North America poleward or produce any arrangement that might result from turning a globe in your hands.

People have been batting around some version of the pole shift hypothesis since at least the mid-19th century and, although many of the scientific questions it attempted to answer have since been addressed by plate tectonics, it's rooted solidly in physics. Plate tectonics and pole shifts interact and are governed by the same forces, but pole shifts, in which the outer shell of the world moves as one piece, produce very different results than plate tectonics, in which pieces of the Earth's crust bump, grind and slide -- opening seas, building mountain ranges and rearranging continents.

If a large pole shift could happen suddenly, the redistribution of land and water it caused would be nothing short of cataclysmic. In the short term, it would mean earthquakes, strange weather patterns, massive tsunamis capable of drowning parts of continents, and possibly gaps in the planet's magnetic field -- our shield against harmful cosmic rays. In the long term, the redistribution of land and water in the tropics, subtropics and poles would fundamentally alter ocean currents and the heat balance of the Earth, resulting in widespread climatological shifts. Ice caps might melt and reform elsewhere, or remain melted, driving sea levels down or up.

All of which returns us to the question: Could such a catastrophic shift occur, and if so, will it happen in 2012? We'll tell you next -- if the world doesn't end before you click to the next page.