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"Long before it's in the papers"
February 11, 2008

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Slow boom-and-bust cycle found in marine life

March 11, 2005
Special to World Science
The number of different types of marine animals alive swells and shrinks every 62 million years, researchers say in a new paper, and no one can explain the pattern. 

A painting by David Miller depicting life in the ocean about 75 million years ago. At the front is a mosasaur, a type of marine reptile. (Courtesy North Dakota Heritage Center, State of North Dakota)
Robert Rohde and Richard Muller detected the cycle in a well-known database showing the growth in fall in the numbers of different types of animals over the last 542 million years.

The cycle is too regular to occur by chance, reported the authors, who are with the University of California at Berkeley. Statistical analyses of the cycle confirm its significance, they added. The findings are described in the March 10 issue of the research journal Nature.

The pattern is not easily explained by geophysical or astronomical explanations, such as periodic comet showers triggered by a companion star to the Sun, researchers said. But the search is on for what is driving the cycle.

One possibility is that it somehow drives itself, wrote two other scientists, James W. Kirchner and Anne Weil, in a commentary published in the same issue of the journal.

“Global biodiversity is a tapestry that weaves itself, so the 62-million year cycle in fossil diversity need not be generated by similar cycles in external driving factors,” they wrote. “Instead, biodiversity could swing like a pendulum, with a rhythmic cycle that is governed by its own internal dynamics rather than by rhythmic external forcing.”

On the other hand, “if the 62-million-year cycle is caused by a biological pendulum,it swings so slowly that it will be challenging” to figure out what causes it, wrote Kirchner and Weil, who are with the University of California at Berkeley and Duke University in Durham, N.C., respectively.

“It is often said that the best discoveries in science are those that raise more questions than they answer, and that is certainly the case here.”

—EJL

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WORLD SCIENCE

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