Astrophysical phenomena and mass extinctions

Various : Cosmologist Adrian Melott has been researching for some time mass extinctions in the Earth’s fossil records and linking them to astrophysical events.Recently, Melott and Brian Thomas looked at the Ordovician extinction , which occurred 450 million years ago and resulted in the loss of 60% of marine invertebrates.According to computer simulations and matched with the fossil record, they find that their data suggests that photons from a gamma-ray burst approximately over the South Pole (and no further than -75 degrees) caused the atmosphere’s chemistry to change, doubling the level of ultraviolet-B solar radiation reaching the surface.In this scenario parts of north China, Laurentia, and New Guinea—which lay north of the equator—should be a refuge from the ultraviolet effects, and show a different pattern of extinction in the “first strike” of the end-Ordovician extinction, if it was induced by such a radiation event.Melott cautions that gamma-rays or x-rays may not be the main cause for extinction events but could be the trigger for tipping an already stressed environment into a catastrophic event. Related Link Late Ordovician Geographic Patterns Of Extinction Compared With Simulations Of Astrophysical Ionizing Radiation Damage In a broader article in SEED magazine Melott talks about his earlier research on cyclic mass extinctions.There are at least 20 mass extinctions throughout the fossil record that fit a 62-million year cycle. Sometime ago Melott suggested that the solar-system’s orbit around the Milky Way’s center —which oscillates through the galactic plane with a period of around 65 million years, is the key—the galactic magnetic field protects the solar-system from extragalactic cosmic rays.As the solar system “bobs” out of the galactic plane it becomes exposed to these cosmic rays which can cause enhanced cloud formation and depletion of the ozone layer, killing off many small organisms at the base of the food chain and potentially leading to a population crash. Related Links The Extinction Oscillator Do Extragalactic Cosmic Rays Induce Cycles in Fossil Diversity? Related Physics Today article Recent Nearby Supernovae May Have Left Their Marks on Earth May 2002