Life on earth follows a mysterious 62 million year cycle that has left researchers stumped for an explanation.

An analysis of fossil records for the past 542 million years shows that biodiversity fluctuates according to the cycle, which holds true for both extinctions and new species. Physicist Richard Muller and his grad student Robert Rohde, working for the DoE's Lawrence Livermore Lab, discovered the cycle in 2003, but have been unable to explain it.

The pair examined 14 different possible explanations but couldn't find a relationship that held up. Rohde's personal hunch is that it's related to volcanic activity, but equally, he says, it could relate to the earth's passage through the Milky Way. Muller suspects that gravitational attraction from stellar objects such as galaxies or molecular clouds could in turn influence the number of genera.

The pair also noticed a 140 million cycle but since the period covered by fossil records only permits four of these, they're reluctant to draw a conclusion. ®

Related link

Livermore Labs press release [thanks Jorn]

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