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Heading Due SouthScripps researchers gather geomagnetic signs to determine if Earth's magnetic field is currently headed toward a complete reversal.June 2008By Annie Reisewitz The Northern Lights illuminate the night sky in Hawaii, wary travelers orient their compasses with the South Pole and birds no longer fly south for the winter. These aren't scenes from the latest sci-fi thriller, but potential real-life consequences of a geomagnetic field reversal. Earth's magnetic field has been steadily weakening since 1845, when scientists began tracking it. Its strength has waxed and waned throughout Earth's history and sometimes, at its weakest moments, has reversed in polarity. Reversals happen on average every 250,000 years, and the last full reversal occurred 780,000 years ago, which suggests the next one is overdue. "The current field protects us from cosmic rays as well as shields our power and communications systems from bombardment by particles in the solar wind," said Cathy Constable, director of the Earth Sciences section and professor of geophysics at Scripps Institution of Oceanography at UC San Diego. "A severe decrease in the field could produce effects similar to a very bad magnetic storm and would have an adverse impact on the communication systems we have today."  
Without this protective shield, life on Earth would confront a much harsher environment. The magnetic field shields the earth, and a network of telecommunications satellites, from a steady stream of particles flying off the sun. A weak field would leave Earth vulnerable to geomagnetic storms that could disrupt electrical grids and telecommunication satellites, widen the ozone holes in the atmosphere and cause more frequent and southerly displays of auroras, including the most famous, the Northern Lights. Many animals such as birds, fishes, turtles, and bees also rely on the magnetic field to navigate. A weak field or change in its direction could interrupt natural migration patterns to spawning and feeding grounds. The magnetic field's mysterious origin and unpredictable reversals are intriguing to scientists, not just to science fiction enthusiasts. Constable and other scientists at Scripps are keeping tabs on the field in order to better understand what drives these fluctuations deep within the earth's core.  
Scripps scientists are in search of geomagnetic clues frozen in time. As lava erupts over the earth's surface and cools, forming rocks, the magnetic moments in particles partially align with the current state of the field. Researchers use this information, along with magnetic traces left behind in sedimentary rocks and ancient ceramics that have been fired, to create a global timeline that can fit the current field changes trend into their historical context. Next page: Digging Into the Past |
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