Cosmic rays produced at the edge of our galaxy have devastated life on Earth every 62 million years.National Geographic News:
The researchers discovered that high rates of extinction in the cycle coincide almost perfectly with periodic "excursions" of the solar system outside the central plane of the Milky Way galaxy.
At regular intervals, the system's wanderings take it up and down through the thin central portion of the disk. The sun reaches its farthest distance from the central plane every 62 million years.
During these periods, which include some of the largest mass extinctions known from the fossil record, Earth is bombarded with high levels of cosmic radiation.
Mikhail Medvedev and Adrian Melott, both of the University of Kansas, presented their new theory at a meeting of the American Physical Society earlier this month.