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As reported by Reuters, USA Today, CNN Online, and Science News, 7/25/97

500 million years ago, an unprecedented evolutionary explosion occurred that resulted in the sudden appearance of a multitude of new life forms around the world. What caused the spurt has long perplexed scientists. Now California Institute of Technology geologists Joseph Kirschvink, David Evans and Robert Ripperdan have determined that the sudden diversification of life forms took place at the same time as Earth's supercontinents took a 90-degree turn, shifting the polar masses to the equator and putting equatorial points at the poles.

Both events occurred during the so-called Cambrian period when, according to Kirschvink, "Life diversified like crazy. About 15 million years later life's diversity had stabilized at much higher levels." Geophysical evidence collected from rocks deposited before, during and after the evolutionary speedup, "demonstrate that all of the major continents experienced a burst of motion during the same interval of time."

Kirschvink said the "evolutionary big bang" took place when life forms existing in cold temperatures were thrust into warmer regions, and vice versa. The ensuing environmental changes created the chaotic conditions needed for rapid evolution. Before the Cambrian period, almost all life was microscopic; at the start of the Cambrian, animals burst forth in a rash of evolutionary activity never since equaled - some 20 times more intense than anything seen before or since. "Something like 40 different major groups of animals make their first appearance during this time," says Kirschvink. "It's an incredible bloom." It was during this "Cambrian explosion." that many multi-celled organisms emerged whose descendants, including human beings, populate the Earth today.

In order to change their positions so radically, the supercontinents that existed at the time would have traveled several feet per year over a 10 million to 15 million year period, compared to continental migration rates today of only a few inches a year. The phenomenon is known as "true polar wander," in which the entire solid part of the planet moves together. Gondwanaland, which consisted of modern-day Africa, Antarctica, Australia, India, and South America, for example, traveled clear across the Southern Hemisphere, and North America shifted its position from the North Pole to the equator. It is thought that the continents shifted as a means of redistributing weight. Such an event might occur when polar land masses become top and bottom heavy relative to the Earth's axis and spin.