Cycles in Fossil Diversity - Astronomy or Geophysics?

Richard Muller

We recently analyzed the most complete record of marine animal fossils ever compiled, the "Compendium" of Jack Sepkoski, which lists all known fossil marine animal genera back 542 million years. When the fossil diversity (number of distinct genera) is plotted, it shows a very strong 62 Myr cycle. The cycle is particularly evident in the species that endured for relatively short times. We examined many possible causes for this cycle, including movement of the Earth through the Galaxy, volcanic eruptions from the core of the Earth, variations in the energy output of the Sun, comet bombardments from solar system perturbations, an intrinsic biological cycle, and more.

No known mechanism accounts for the cycles. There is one other strong cycle in the data, with period 140 Myr. This matches a previously known climate cycle, and may be due to the passage of the Earth through the arms of our galaxy.