A puzzlingly regular waxing and waning of Earth's biodiversity may ultimately trace back to our solar system's bobbing path around the Milky Way, a new study suggests.

Every 60 million years or so, two things happen, roughly in synch: The solar system peeks its head to the north of the average plane of our galaxy's disk, and the richness of life on Earth dips noticeably.

Researchers had hypothesized that the former process drives the latter, via an increased exposure to high-energy subatomic particles called cosmic rays coming from intergalactic space. That radiation might be helping to kill off large swaths of the creatures on Earth, scientists say.

The new study lends credence to that idea, putting some hard numbers on possible radiation exposures for the first time. When the solar system pops its head out, radiation doses at the Earth's surface shoot up, perhaps by a factor of 24, researchers found.

"Even with the lowest assumption, this exposure provides a real stress on the biosphere periodically," said lead author Dimitra Atri of the University of Kansas, who presented the findings last week at the fall meeting of the American Geophysical Union in San Francisco.