Magnetic Havoc

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 of the sea bottom drilled in the Pacific and Antarctic oceans. After microscopic examinations of half a million individual fossils taken from the deep-sea cores, Paleontologist James D. Hays and Geophysicist Neil Opdyke concluded that two species of Radiolaria became extinct 2.4 million years ago, another about two million years ago, two about 1.8 million and one about a million years ago. The dates, Hays told a meeting of the Geological Society of America, are significantly close to known reversals in the earth's field.

Vanishing Field. Exactly how the reversals could have wreaked such biological havoc is a matter of dispute. Some investigators have theorized that the deterioration in the earth's protective magnetic shield during reversals of the magnetic poles allowed an increased amount of damaging solar radiation to reach the earth. More recently, a number of geophysicists have calculated that even if the magnetic field completely vanished during reversal, the additional radiation would not be intense enough to destroy entire species. As a result, some investigators are beginning to think that the changed magnetism itself may somehow have been responsible.

If dinosaurs were affected by magnetic reversals, could they also harm higher animals like man? No one knows the answer, but the question may not be entirely academic. In the past 10 million years, the earth's magnetic poles have reversed themselves, on the average, every 220,000 years. But the last event occurred 700,000 years ago --which means that another switch is now long overdue.

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