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University Relations

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Jan. 8, 2009
Contact: Brendan M. Lynch, University Relations, (785) 864-8855.

KU researcher unearths new proof of die-off timetable

LAWRENCE — Evidence uncovered by a University of Kansas researcher strongly supports the prospect that biodiversity on Earth grows and shrinks in a regular 62-million-year cycle, give or take a few million years.

Adrian Melott, professor of physics and astronomy at KU, published his findings in the Dec. 24 edition of PLoS ONE, a peer-reviewed online publication.

In his article, Melott shows that fossils of marine invertebrates in the Paleobiology Database confirm 2005 findings of regular die-offs by separate researchers using another set of fossils.

“The same signal has been found in completely different data sets, making the likelihood that it’s a real signal much greater,” said Melott. “Since the data sets were constructed independently, and treated very differently by those who constructed them, this makes the chances vanishingly small that it is merely a coincidence.”

The 62-million-year fluctuation in the array of life on Earth first was discovered in the Sepkoski data set and made public by University of California-Berkeley researchers Robert Rohde and Richard Muller.

“Fossil biodiversity is a count of how many different kinds of creatures exist on the Earth at a given time,” Melott said. “This number has been generally increasing for the last 500-plus million years. But there have been a lot of ups and downs within this trend. The pattern of these ups and downs includes a strong 62-million year cycle that Rohde and Muller said had a 1-in-100 chance of being a fluke, or chance happening. They had no explanation for why such a regular pattern should exist.”

Last year, Melott and colleague Mikhail Medvedev, associate professor of physics and astronomy, offered a novel explanation for the pattern of disappearing species.

The KU researchers proposed that the periodic die-offs might have a celestial cause. Melott and Medvedev showed that the seesawing motion of the solar system exposes Earth to an onslaught of cosmic rays on a schedule that is synchronized to the mass extinctions.

“Cosmic rays may irradiate life forms on the ground, as well as change the atmosphere in ways that expose life to more cancer-causing UVB radiation and possibly cause additional cloud cover,” Melott said. “These stresses could act together with other things that happen, such as asteroid impacts or periods of increased volcanoes.”

Despite his contention that the Earth inevitably will undergo another dose of higher-than-ordinary cosmic ray exposure, Melott assured that a die-off will not happen anytime soon — at least not one triggered by the motion of the solar system.

“Everyone always asks where we are in the 62-million-year cycle,” said Melott. “According to that cycle, biodiversity should be on the way down now, reaching bottom within a few million years.”

On Jan. 12 on the National Geographic Channel, Melott will appear in the Naked Science episode “Extinctions,” which addresses similar themes.

Melott’s article is available on the Web site for PLoS ONE.


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