Friday, Jun. 17, 1966

Flipping the Magnetic Field

Every half-million years or so, for unknown reasons, the earth's magnetic field suddenly flips. Within a period of 10,000 years--a mere instant on the geological time scale--the north and south magnetic poles exchange places. Scientists have long suspected that the mysterious reversals may produce major changes in the earth's topography. Now it seems that there may be even more far-reaching effects. A group of Columbia University scientists has collected evidence suggesting that the flipping field may also play a major role in the evolution of terrestrial life.

Working with 32-to 65-ft.-long sedimentary cores taken from the bottom of the North Pacific, Geologist Bruce Heezen and his associates at Columbia's Lamont Geological Observatory carefully examined each one, slice by slice, for traces of residual magnetism and remnants of primitive life. Because sediment has settled continuously on the ocean bottom for millions of years, each core represented both a magnetic and evolutionary calendar; each slice was a thin but significant record of a brief period in the earth's history.

Analysis of the slices, Heezen reported to an oceanographic conference at Moscow University, showed that the most recent magnetic-field reversal occurred about 700,000 years ago, following earlier flips 2,500,000 and 3,500,000 years ago. Fossil remnants in the slices also indicated that several new species of algae and protozoa suddenly appeared about 2,500,000 years ago and existed without significant change until 700,000 years ago. Then, within a short time span, some of those species completely disappeared, others underwent marked change, and new species emerged.

The evolutionary changes, Heezen believes, may well have been caused by the temporary disappearance of the earth's magnetic field at the mid-point of each reversal cycle. In the absence of the field--which normally deflects many of the high-energy particles from outer space--cosmic-ray particles rained down unhindered. Enough of them penetrated the atmosphere to alter and damage the cells of existing organisms, destroying some species and causing mutations in others.

Man appeared on earth after the last reversal, and he has never been exposed to a significant increase in cosmic radiation. But he soon may be put to the test. Current data, Heezen feels, points to a gradual weakening of the magnetic field, a possible prelude to a reversal in a few hundred to a few thousand years. This would mean a sudden increase in cosmic bombardment of the earth's surface. "I don't want to be an alarmist," he says, "but we may be next."

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