Radical Shift

Reuters 24-JUL-97 By Michael Miller

A 90-degree shift of the Earth's early continents - in which the North and South Poles wound up at the equator -- may have played a major role in the evolutionary “big bang” that speeded up the development of life, scientists said. A report to be published on Friday in the journal Science said the “big bang,” a sudden spurt in the evolutionary process, began about 530 million years ago and proceeded at a rate 20 times faster than anything that has happened since.

What caused that spurt has long been a mystery perplexing scientists; now experts at the California Institute of Technology (Caltech) say they may have part of the answer. Caltech geologists Joseph Kirschvink and David Evans and Robert Ripperdan of the Oak Ridge National Laboratories in Tennessee said the relatively sudden diversification of life forms took place at the same time as Earth's then-super continents 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 a major reorganization of the Earth's crust took place. They said in Science that all the data ”indicate that rapid continental drift occurred during the same time interval as the Cambrian evolutionary diversification and, therefore, the two events may be related.” Kirschvink said, “Life diversified like crazy about a half a billion years ago, and about 15 million years later life's diversity had stabilised at much higher levels. What actually happened is one of the outstanding mysteries of the biosphere.” He added that the 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.”

Evans told Reuters the study indicated that in order to change their positions so radically, the super continents - which broke up about 150 million years ago to form today's continents - would have travelled several feet (metres) per year over a 10 million to 15 million year period. The phenomenon is known as ”true polar wander,” in which the entire solid part of the planet moves together. Typical continental migration rates today, which are caused by heat convection in the Earth's crust, are only a few inches (centimetres) a year, Evans said. Kirschvink said the climatic changes, in which life forms existing in cold temperatures were thrust into warmer regions, and vice versa, forced their diversification as they adapted to their new environments. It also produced a survival of the fittest pattern of evolution in which certain groups died off and others became stronger through survival.

Of particular significance to the scientists was the once super continent of Gondwanaland, probably made up of what is now Australia, Antarctica, India, Africa, South America and perhaps parts of East Asia. Studies of rocks found in Australia and dating back to the Cambrian period “demonstrate that Australia rotated counter- clockwise during this time. Other parts of the Gondwanaland super continent must have been involved in this ... rotation,'“ the report in Science said.