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Sea Floor Was Spreading:
At first sight sea-floor spreading appears to be an idea of science fiction, and some earth scientists received it as such. In the last two years, however, enough data have become available to convince most geophysicists that the hypothesis of sea-floor spreading is essentially correct, although there is disagreement on the details. Even though the hypothesis had been postulated on geological grounds, it was dramatically verified by recent geophysical studies concerning the earth's magnetic field.Vine and Matthews used the reversals of the earth's magnetic field to test the hypothesis of sea-floor spreading in an ingenious way. Precise measurements of the magnetic field in the oceans showed that large areas of the seabed are magnetized in long, narrow strips of alternately high and low magnetization, and the suggestion was made that this is due to sea-floor spreading during reversals of the magnetic field. Molten rock rising on the axis of an ocean ridge would cool and become magnetized by the earth's field. Spreading would carry these magnetized rocks laterally away from the ridge on both sides.
Whether a catastrophic event—a great earthquake, or the impact of a meteorite, or natural processes inside the earth's core—causes the reversal remains a mystery. At the same time that evidence for magnetic reversal was accumulating, the theory that the sea Floor was spreading began to have currency among geophysicists. According to this theory, lava issues forth from mid-oceanic fractures, creating new crust on the sea floor. Repeated opening of the fractures must therefore produce spreading.
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