Two years ago physicist Richard Muller (University of California, Berkeley) and his student Robert Rohde discovered a 62-million-year periodicity in the wordwide diversity of marine animals. 1 They had undertaken a Fourier analysis of the time variation of the total number of genera listed in John Sepkoski's authoritative Compendium of Fossil Marine Animal Genera, which begins about 542 Myr ago—when animals first developed the hard exo- and endo-skeletons that facilitate fossilization.
Sepkoski and coworkers at the University of Chicago had been compiling this valuable data set for decades until his death in 1999. Dating the first appearances and final disappearances of tens of thousands of genera depends crucially on age estimates of the stratigraphic layers in which their fossils are found. In 2004 the International Commission on Stratigraphy released a much improved chronology of very old strata based on the best available radioactive potassium–argon dating. “As soon as we...
