Northern Exposure: The inhospitable side of the galaxy?
The solar system’s periodic visits to the northern side of the Milky Way expose life on Earth to extra cosmic rays that have caused catastrophic mass extinctions, two astrophysicists propose.
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Biodiversity has had well-known ups and downs over the eons, with major extinctions followed by rebounds. In a 2005 study, Robert Rohde and Richard Muller of Lawrence Berkeley (Calif.) National Laboratory found that these swings were surprisingly regular, most of them taking place at intervals of about 62 million years. The researchers reached their conclusion after examining one of the most comprehensive long-term biodiversity surveys, a compilation of fossil data that charted the number of marine-life genera over the past 500 million years.