The collapse of the earth's magnetic field, which both guards the planet and guides many of its creatures, appears to have started in earnest about 150 years ago, the NY TIMES is planning to report on Page One Tuesday.

Science reporter Bill Broad has filed a report, according to newsroom sources, which explores how: 'The field's strength has waned 10 percent to 15 percent so far and this deterioration has accelerated of late, increasing debate over whether it portends a reversal of the lines of magnetic force that normally envelop the earth."

Broad explains: "During a reversal, the main field weakens, almost vanishes, and then reappears with opposite polarity. Afterward, compass needles that normally point north would point south, and during the thousands of years of transition much in the heavens and Earth would go askew."

Broad claims: "A reversal could knock out power grids, hurt astronauts and satellites, widen atmospheric ozone holes, send polar auroras flashing to the equator and confuse birds, fish and migratory animals that rely on the steadiness of the magnetic field as a navigation aid.

Below is a computer simulation showing the Earth's interior as its magnetic field reverses, perhaps because of changes in the flow of molten iron in the core.

See New York Times article (registration required):

http://www.nytimes.com/2004/07/13/science/13magn.html