Australian scientists say they've determined the rate of evolution's "big bang" when most modern animal groups appeared around 530 million years ago.

The findings are considered an answer to "Darwin's dilemma," the sudden and unexpected appearance of a large number of modern animal groups in the fossil record during the early Cambrian period.

"The abrupt appearance of dozens of animal groups during this time is arguably the most important evolutionary event after the origin of life," lead author Michael Lee of the University of Adelaide's said.

"These seemingly impossibly fast rates of evolution implied by this Cambrian explosion have long been exploited by opponents of evolution," he said in a university release Thursday. "Darwin himself famously considered that this was at odds with the normal evolutionary processes."

The researchers, working with colleagues from the Natural History Museum in London, analyzed the anatomical and genetic differences between living animals and, with the help of the fossil record and mathematical models, developed a time frame over which such differences would have accumulated.

The findings suggest moderately accelerated evolution was sufficient to explain the seemingly sudden appearance of many groups of advanced animals in the fossil record during the Cambrian explosion.

"In this study we've estimated that rates of both morphological and genetic evolution during the Cambrian explosion were five times faster than today -- quite rapid, but perfectly consistent with Darwin's theory of evolution," Lee said.