Source: AP (Associated Press)
Date: July 25th 1997

WASHINGTON (AP) - A `sudden' rotation of the Earth's surface 530 million years ago coincided with and may explain a huge increase in new forms of plant and animal life, scientists reported.

This rotation one-quarter around the globe occurred during 15 million years - the same period as the `Cambrian explosion' of new species, California Institute of Technology researchers report in the journal Science.

Geologist Joseph Kirschvink and his colleagues said their work is still speculative.
They analyzed the magnetic fields of ancient rocks to pinpoint their locations up to 600 million years ago. If they are correct, the simultaneously emerging life forms would have adjusted to dramatically changing climates - from poles to tropics - in a far shorter span than biologists thought possible.

The Earth's land was a massive supercontinent in this period with the poles clustered near the equator. Scientists even have found a dinosaur fossil in Antarctica that attests to the shifting mass.

The question was how the land got there. A leading theory is tectonic motion, where heat deep inside the Earth's crust moves continental plates a few inches a year. That movement continues today.

Scientists also have long known that the planet spinning on its axis could make its surface shift, and Kirschvink's study suggests this 'true polar wander' is the explanation.

He wrote that as Earth spun, land concentrated at the poles was pushed toward the equator at a speed of several feet per year. Resulting shifts in ocean currents would have changed climates and sped evolution, he explained.

AP-NY-07-25-97

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