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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