New twist on the history of life.

PositionCambrian Explosion

The idea that the wholesale relocation of Earth's continents 520,000,000 years ago, also known as "true polar wander," coincided with a burst of animal speciation in the fossil record dates back almost 20 years to an original hypothesis by Joseph Kirschvink, professor of geobiology at the California Institute of Technology, Pasadena, and his colleagues. For more than a century, paleontologists, including Charles Darwin, have debated whether the so-called Cambrian Explosion--a rapid period of species diversification that began around 542,000,000 years ago--was the equivalent of an evolutionary "big bang" of biological innovation or just an artifact of the incomplete fossil record.

In a study published in the American Journal of Science, a team of researchers--including Kirschvink and Ross Mitchell, a postdoctoral scholar in geology at Caltech--describes a new model showing that, during the proposed Cambrian true polar wander event, most continents would have moved toward the equator instead of toward the poles.

"It's long been observed that biological diversity is highest in the tropics, where nutrients and energy tend to be abundant," says Kirschvink. "One of the side effects of true polar wander is that sea...

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