Magnetic minerals in 15-million-year-old Nevada rocks appear to preserve a moment when the magnetic north pole was rapidly on its way to becoming the south pole, and vice versa. Such “geomagnetic field reversals” occur every couple hundred thousand years, normally taking about 4,000 years to make the change. The Nevada rocks suggest that this particular switch happened at a remarkably fast clip.
" Magnetic Flip-FlopsConsidering that ships, planes and Boy Scouts steer by it, Earth's magnetic field is less reliable than you'd think. Rocks in an ancient lava flow in Oregon suggest that for a brief erratic span about 16 million years ago magnetic north shifted as much as 6 degrees per day. After little more than a week, a compass needle would have pointed toward Mexico City.
The lava catches Earth's magnetic field in the act of reversing itself. Magnetic north heads south, and -- over about 1,000 years -- the field does a complete flip-flop. While the Oregon data is controversial, Earth scientists agree that the geological evidence as a whole -- the "paleomagnetic" record -- proves such reversals happened many times over the past billion years.
"Some reversals occurred within a few 10,000 years of each other," says Los Alamos scientist Gary Glatzmaier, "and there are other periods where no reversals occurred for tens of millions of years." How do these flip-flops happen, and why at such irregular intervals? The geological data, invaluable to show what happened, registers only a mute shrug when it comes to the deeper questions.
For that matter, why is it that instead of quietly fading away, as magnetic fields do when left to their own devices, Earth's magnetic field is still going strong after billions of years? Einstein is said to have considered it one of the most important unsolved problems in physics. With a year of computing on Pittsburgh's CRAY C90, 2,000 hours of processing, Glatzmaier and collaborator Paul Roberts of UCLA took a big step toward some answers. Their numerical model of the electromagnetic, fluid dynamical processes of Earth's interior reproduced key features of the magnetic field over more than 40,000 years of simulated time. To top it off, the computer-generated field reversed itself.
"We weren't expecting it," says Roberts, "and were delighted. This gives us confidence we've built a credible bridge between theory and the paleomagnetic data." Their surprising results, reported as a cover story in Nature (Sept. 21, 1995), provide an inner-Earth view of geomagnetic phenomena that have not been observed or anticipated by theory. Furthermore, the Glatzmaier-Roberts model offers, for the first time, a coherent explanation of magnetic field reversal.....more here ..."
Anyone carrying a compass would have seen its measurements skew by about a degree a week — a flash in geologic time. A paper describing the discovery is slated to appear in Geophysical Research Letters.
It is only the second report of such a speedy change in geomagnetic direction. The first, described in 1995 based on rocks at Steens Mountain, Ore., has never gained widespread acceptance in the paleomagnetism community. A second example could bolster the theory that reversals really can happen quickly, over the course of years or centuries instead of millennia.
Researchers aren’t sure why the geomagnetic field reverses itself. Many think it must have something to do with what creates the field in the first place — convective motions of liquid iron in the planet’s spinning outer core. As each flow cooled, it preserved the orientation of the magnetic field at the time, frozen like a tiny compass needle in the rock’s magnetic crystals.
One particular flow caught the scientists’ attention because it seemed to carry a complex magnetic history. The lava, initially started to cool and then was heated again within a year as a fresh lava flow buried it. The fresh lava remagnetized the crystals within the rock below, causing them to reorient themselves a whopping 53 degrees. At the rate the lava would have cooled, that would mean the magnetic field was changing direction at approximately 1 degree per week.
The Steens Mountain rocks have been reported to preserve a change of 6 degrees per day. That rate was so high — imagine trying to navigate when a compass changes by multiple degrees per day — that many scientists challenged the report. One line of argument held that the liquid outer core simply can’t generate magnetic field changes that rapidly. Another held that, even if the changes were happening, they wouldn’t be observable at the surface because the Earth’s internal electrical conductivity would screen the signals out.
" Steens Mountain looms on the horizon like a giant stone battleship becalmed on a vast, placid sea. Sixteen million years ago, a series of immense flows of lava gushed forth across those plains. Erosion has since claimed most of the lava flows, but the mountain remains, stretching 60 miles from north to south. Massive lava flows are common historically, but Steens Mountain contains geologic oddities so unexpected that they may profoundly alter our perception of the inner workings of our planet.
In the center of the Earth sits a dense core of nickel and iron, roughly 2,000 miles in diameter. Geophysicists, who study the Earth's interior, believe the inner core to be solid and the outer core fluid. A layer of solid rock 1,800 miles thick called the mantle surrounds the outer core. Atop the mantle rests the Earth's crust, the thin layer where mountains form, and wind and water wear them down.
Geophysicists think the fluid in the outer core circulates, with currents driven by gravitational and thermal forces interacting with the Earth's rotation. The currents are thought to travel roughly six to twenty miles per year.
This circulation in the iron-rich outer core generates the global magnetic field, the helpful force that guides not only compass needles but also, as biologists are finding, a wide variety of animals, from bacteria to seagoing turtles.
Yet the Earth's magnetic field is not as reliable as one might expect. Paleomagnetists, scientists studying the history of the magnetic field, learned 30 years ago that the polarity of the field occasionally reverses. If the field were reversed now, compasses would point south instead of north. Many scientists believed that these reversals happened slowly, in a series of short steps, taking roughly 5,500 years. But the rocks in Steens Mountain record episodes when the field was moving up to six degrees in a single day, a burst of speed over 1,000 times faster than expected. How the relatively slow-moving fluid in the outer core can generate such rapid changes is a mystery. .... more ..."
The last stable reversal occurred 780,000 years ago. Some geologists argue the Earth is overdue for a reversal and might even be entering one now, as the geomagnetic field has been getting weaker over the past 150 years or more.
But apocalyptic SyFy channel movies to the contrary, nobody should worry about waking up one morning to geomagnetic havoc. To geologists a polarity reversal is a nearly instantaneous thing that changes a global feature of the Earth — it’s really a spectacular phenomenon.
" Strictly speaking there are two types of polar reversal. One is the reversal of the planets magnetic poles and the other is a full geographical tilt of the Earth on its axis. While it is uncertain whether both would occur in tandem, some experts believe that the two are intricately linked. The last known reversal of the magnetic poles occurred around three quarters of a million years ago. Scientists point out that since there were no mass extinction's at that time the effects on existing life must have been relatively benign. Even so a magnetic polar reversal would result in a lessening of the planets magnetic field allowing harmful solar rays to penetrate to the surface of the planet.
It goes without saying that a full polar reversal, involving the geographic poles of the planet would be a much different proposition to the relatively tame magnetic reversal. A full polar reversal would be a highly catastrophic event, capable of destroying all life on Earth. It would also fall into that category of event over which we have absolutely no control whatsoever. In fact there are those who believe that full polar reversals are no more than a routine - if catastrophic event which happen according to regular cycles built-in to the Earth’s rotational mechanism.
In many ways the ancient world understood this cycle of events far more intimately than we do today. They understood that as one day gives way to the next, there were periods when the Earth quite literally convulsed in a huge fit of turbulence that was no more than a routine element of the planet we live on. A destructive cycle that was repeated again and again.
The ancient Greek philosopher Plato in his dialogue The Statesman adds further to the mystery saying: “At periods the universe has its present circular motion, and at other periods it revolves in the reverse direction.....Of all the changes which take place in the heavens this reversal is the greatest and most complete.” Plato warns this period of reversal is far from orderly: “There is at that time great destruction of animals in general, and only a
The exact reasons behind polar reversals are not fully understood. What we do know is that they tend to happen when there is a wide divergence between the magnetic poles and their geographic equivalent, as is currently the case. Another possible reason is that the Earth is grossly unbalanced. The greatest north/south ( see here for pic) area of landmass is immediately opposite the greatest body of unbroken Ocean, stretching from pole to pole. Since land weighs more than water, this makes one side of the world very much heavier than the other. It also means that given the force of some unsettling influence - possibly an asteroid strike, the planet could quite literally topple over on its axis.
Another plausible reason for a polar reversal are the effects of vast streams of magma that flow beneath the Earth’s crust. It is thought that when these undergo drastic changes to their rate of flow the resulting surge is enough to topple an already stressed planet on its axis. This could happen when melting polar ice lessens pressure at the poles leading to a surge of magma into the resulting cavity, with catastrophic results.
From ancient and scientific sources we can accurately predict that the next polar reversal is solely a matter of time. When it does happen it will be a catastrophe of epic proportions that will leave few if any survivors. We must therefore hope that its onset continues to delay itself for as long as possible...more... "