Is the Earth about to reverse its magnetic field?

It sure looks that way, but don't hold your breath. It will take several thousand years. These kinds of magnetic field reversals have been going on for millions of years and are analogous to the 11-year sunspot cycle which is probably caused by the same 'magnetic dynamo' mechanism, though speeded up greatly because for the sun the material is a plasma not a conducting metallic liquid. The figure below shows the reversals identified in the strata around the mid-Atlantic ridge:

For more information, have a look at the Academic Press page on latest simulations of magnetic reversals using a physics-based model. I will reproduce that page here:

Computer simulations now suggest that the planet's rocky mantle, rather than its outer core of liquid iron, controls the mysterious rhythms of these reversals. However, the simulations still don't reveal the processes that start and stop each swing of the compass, according to a report in tomorrow's issue of Nature (ca. October 27, 1999).

Although the field clearly originates in the planet's metallic core, some researchers have speculated that slow churnings in the overlying mantle must affect when and how magnetic chaos strikes. To explore that claim, geophysicists Gary Glatzmaier of the University of California, Santa Cruz, and Paul Roberts of UCLA created a supercomputer model that mimics the flow of fluid within Earth's electrically conducting outer core. Four years ago, this model achieved the first accurate simulation of a magnetic flip-flop. Now, the team has run its code long enough to see many such reversals. By altering the pattern of heat flowing from Earth's core into the lower mantle, the researchers were able to increase the frequency of the simulated reversals or suppress them entirely. The flow of heat changes within the real Earth when cold slabs of crust from the surface sink into the mantle over periods of tens of millions of years, Glatzmaier notes: "Reversals are complicated and chaotic, but these mantle motions may have some long-term influence by pumping more heat out of the core." Geophysicist Bruce Buffett of the University of British Columbia in Vancouver lauds the work as "the first systematic study of the geodynamo that exhibits proper reversals." Even so, he cautions that the model is not yet detailed enough to capture the intricate phenomena that set off each reversal: "It's suggestive that the mantle plays a role, but it's a hard call to say whether the simulations have geophysical meaning." --Robert Irion

Copyright 1997 Dr. Sten Odenwald

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