Every 62 million years there's a collapse in biodiversity. The hypothesis is that this represents some periodic extinction event.
Muller and Rohde have been working on this study for nearly two years, and first discovered the 62 million year biodiversity cycle in November, 2003. They spent the next year trying to either knock it down or explain it. Despite examining 14 possible geophysical and astronomical causes of the cycles, no clear explanation emerged. Muller and Rohde each has his own favorite guess.Or maybe that's how often the galactivc pest-control service visits our solar system. I am most annoyed that the journalist didn't bother to point out where we are in the extinction cycle.
Muller suspects there is an astrophysical driving mechanism behind the 62 million year periodicity.
“Comets could be perturbed from the Oort cloud by the periodic passage of the solar system through molecular clouds, Galactic arms, or some other structure with strong gravitational influence,” Muller said. “But there is no evidence even suggesting that such a structure exists.”
Rohde prefers a geophysical driver, possibly massive volcanic eruptions triggered by the rise of plumes to the earth’s surface. Plumes are upwellings of hot material from near the earth’s core that some scientists believe have the potential to reoccur on a periodic basis.
“My hunch, far from proven,” Rohde said, “is that every 62 million years the earth is releasing a burst of heat in the form of a plume formation event, and that when those plumes reach the surface they result in a major episode of flood volcanism. Such volcanism certainly has the potential to cause extinctions, but, right now there isn't enough geologic evidence to know whether flood basalts or plumes have been recurring at the right frequency.