At least 171 times in the past 76 million years, the earth's magnetic field has mysteriously faded in strength and then returned to normal with the North and South poles reversed. Scientists have long suspected that these reversals may somehow be linked with such old biological puzzles as the sudden disappearance of the dinosaurs some 65 million years ago. Now investigators from Columbia University's Lamont-Doherty Geological Observatory have added new evidence to the old speculations. They report that six species of Radiolaria—tiny marine animals—suddenly became extinct during or shortly after switches in the earth's magnetic poles.
The evidence comes from 28 samples...
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