Questions answered

By Sherry Seethaler

SAN DIEGO UNION TRIBUNE
December 15, 2004

QUESTION: As Earth approaches a magnetic shift, what effect will this have on the polarity of electricity from our generators? Also, how will this affect the navigation of birds and sea creatures and us when it reaches null? And what about the warming of Earth and skin cancer when our protective magnetic field is gone?

– Dennis Kedziora, Santee

ANSWER: The strength of Earth's magnetic field has decreased about 10 percent since 1845. Scientists think the polarity of the field might flip (magnetic north and south changing places) within a few millenniums. The last flip occurred 780,000 years ago.

Changes in the strength or orientation of Earth's magnetic field could result from changes in the rotation rate or electrical conductivity of the molten iron in the earth's core, which is thought to produce the field.

Previous polarity reversals are documented in rock. For example, along the mid-Atlantic volcanic ridge where the continental plates are separating, there are stripes of rock with alternating polarity. Each stripe reflects the polarity of the field that existed when the rocks were made, because magnetic particles in molten rocks align with Earth's magnetic field before the rocks solidify.

The reversion of Earth's magnetic field to zero during a flip could cause an increase in the amount of cosmic radiation reaching earth's surface, loss of protection from solar flares and navigation problems for some organisms.

Climatologists have failed to find evidence of changes in Earth's temperature or weather patterns occurring in conjunction with magnetic reversals. The fossil record does not reveal any major changes in plant or animal life occurring in conjunction with previous polarity flips. Even without Earth's magnetic field, our atmosphere would still shield us from most cosmic radiation, but cancer rates could increase.

Without Earth's magnetic field to deflect solar flares, they could cause trouble, including damaging the ozone layer.

Many birds and sea creatures rely on the magnetic field to migrate, often combining magnetic cues with celestial cues and information from landmarks.

No one really knows how these animals may adapt to a polarity flip, or how they will migrate should the magnetic field become zero. However, these creatures must have some adaptability because since the 1800s our magnetic north pole has wandered about 700 miles.

copyright 2004 The San Diego Union Tribune