Selasa, 13 September 2011

Pole Shifting In 2012?

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
he 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 shifthypothesis, 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?

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

o understand polar shift (known to geologists as the True Polar Wander, or TPW, hypothesis), it helps to have a clear picture of how the Earth is put together.

The Earth isn't a solid ball of rock; it consists of concentric layers, each with its own heat and density characteristics. The outermost layer, the crust, is made up of rocky, interlocking pieces. These aluminum-silicate plates float like rafts atop a molten outer mantle, which surrounds a more fluid inner mantle. Farther in, a liquid nickel-iron outer core encompasses the Earth's solid, iron inner core. Put another way, the Earth consists of a solid shell surrounding a liquid interior, which encircles a solid center.

Most of the Earth's internal heat is stored in the mantle. There, temperature differentials cause convection -- the same process observed in a pot of boiling water, except it takes place over hundreds of kilometers and involves what Dr. Evil would call "liquid hot magma." Hotter magma rises toward the crust while cooler, denser materials -- such as subducted oceanic plates -- sink toward the core [source: Sager]. Convection drives tectonic processes and also redistributes the internal mass of the Earth.

Above the mantle, the crust tilts, rocks, sinks and rebounds in response to changes in pressure and load, such as occur after an ice age, when glacial ice returns to the sea as meltwater. The motion is like how a boat reacts to a person exiting or climbing aboard, only much slower.

When internal and/or surface mass distributions become uneven, TPW might occur, because the centrifugal force of the Earth's spin drives mass anomalies -- whether on the crust or in the mantle -- toward the equator. Some geologists argue that this has happened in the past. One possibility occurred about 800 million years ago; another, 610 - 510 million years ago, might have caused climate shifts that helped bring about the Cambrian explosion -- the relatively rapid appearance of most of the major groups of animals in the fossil record.

Some scientists believe that a polar shift is happening right now, at a rate of around nearly 4 inches (10 centimeters) per year [source: Tarduno]. This gradual "righting of the boat" is a physical response to the retreat of the Laurentide ice sheet at the end of the Pleistocene Epoch, 20,000-plus years ago [source: Maloof]. But don't pack the kids into John Cusack's limo just yet; this rate, although fast by plate tectonic standards, is still very, very slow. In fact, TPW takes 1 million to 100 million years to complete an adjustment -- the geological equivalent of watching fingernails grow -- and the current one will stop before making much progress.
 However you look at it, rapid polar shifts, like the kind portrayed in the movie "2012," simply don't happen.

Magnetic Shift

Polar shift is easily confused with pole reversal, in which the Earth's magnetic poles change places. Evidence for such reversals is abundant, locked in the iron oxides of ancient rocks, which aligned along the direction of magnetic north when they cooled. This alignment still occurs in some igneous rocks, such as when lava cools and crystallizes. Magnetic pole reversals occur irregularly (around every 300,000 years) and require thousands of years to complete. Some call the South Atlantic Anomaly -- a trough in the Earth's magnetic field near the coast of Brazil that enables cosmic rays and charged particles to delve lower than usual into the atmosphere -- a harbinger of an upcoming pole reversal, due perhaps as soon as 2012. Scientists think it unlikely; even if it happened, they say, the results would not be catastrophic.

 by "environment clean generations"

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