The San Francisco Chronicle reports that
Berkeley scientists have discovered a regular 62 million year cycle of mass extinctions.
Richard Muller and his graduate student, Robert Rohde, are publishing a report on their exhaustive study in the journal Nature today, and in interviews this week, the two men said they have been working on the surprising evidence for about four years.
"We've tried everything we can think of to find an explanation for these weird cycles of biodiversity and extinction," Muller said, "and so far, we've failed."
The idea that mass extinctions happen on a regular cycle isn't exactly new. Most theories such as the Alvarez meteor/comet theory described a 26 to 30 million year cycle. Interestingly, Mueller worked with Alvarez at Berkeley.
Muller's favorite explanation, he said informally, is that the solar system passes through an exceptionally massive arm of our own spiral Milky Way galaxy every 62 million years, and that that increase in galactic gravity might set off a hugely destructive comet shower that would drive cycles of mass extinction on Earth.
Rohde, however, prefers periodic surges of volcanism on Earth as the least implausible explanation for the cycles, he said -- although it's only a tentative one, he conceded.
Of course, according to the Chronicle article, the last major extinction happened 65 million years ago, so we're obviously doomed. "More study is necessary" of course, so keep sending those tax dollars to UC Berkeley, folks.