Author Archives: Michael Froomkin

So the sun has an orbit, or an oscillation, relative to the galactic plane, and when it gets to one of the extremes, we get fried with muons. Could this explain why every 62 million years, there's a huge die-off of species, about ten percent, in our biosphere?

Of Cosmic Rays and Dangerous Days: Now, researchers from the University of Kansas in Lawrence think they have found a possible answer. Physicist and co-author Adrian Melott says that he began suspecting a galactic cause after noticing a 2005 paper that calculated that the drop in species diversity occurs regularly on a time scale of tens of millions of years, which—for a cyclical event—is too long for something happening within the solar system. So he and Kansas colleague Mikhail Medvedev began examining the possibilities. At about the same time as the drops in biodiversity, the researchers determined, the sun reaches the highest point in its orbit relative to the galactic plane, where most Milky Way stars reside. At that point, the scientists report in the 1 August Astrophysical Journal, the solar system is closest to an incoming source of potentially lethal cosmic rays created by interactions between the Milky Way's magnetic field and radiation generated by a cluster of nearby galaxies.

These galaxies are located in the direction of the constellation Virgo, and the radiation consists of particles called muons, which are so powerful they can penetrate about 2.5 kilometers of sea water or 900 meters of rock—enough to reach just about every living thing on Earth and damage its DNA. Because the zenith of the Sun's oscillations match almost exactly with the times of the dips in the fossil record, the researchers found, “we've noticed an incredible coincidence,” Melott says.

Be sure to mark your calendar to give you plenty of warning, as the next one is due in just seven million years.