Seabed movers

Published: Friday 31 January 1997

Tectonic plates on the Pacific Ocean floor are drifting apart faster than expected --15 cm per year at one point -- according to a new study. Researchers can estimate how fast plates drift by studying magnetic signals recorded at the ocean floor. These magnetic signals, which are of different polarities, are generated by lava flowing out of ridges between two plates, creating a new crust. As the lava cools, it records the direction of the Earth's magnetic field through these signals. After about every 500,000 years, the motion of the Earth's liquid outer core reverses the magnetic field and new signals begin to take shape. Douglas Wilson, a geophysicist at the University of California in Santa Barbara, us, re-examined the magnetic profiles of the Pacific. Having dated the bands formed by magnetic signals on the rocks of the seabed, Wilson measured the distance between the bands. Comparison suggested that some of the bands were younger than previously thought and therefore, the plate must have travelled faster than was originally believed ( New Scientist , Vol 152, No 2050).

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