There have been a number of mass extinctions in the Earths history and many reasons provided to explain them. From asteroids colliding with Mexico, to cataclysmic volcanic eruptions ushering in years of winter, and Gamma Ray Bursts from nearby Supernova, there are any number of ways a mass extinction can occur. Now Astophysicists are saying that Gamma Ray Bursts are unlikely to occur in our Galaxy. It seems that Gamma Ray Bursts tend to occur in younger, low metal galaxies. Metal meaning elements heavier than lithium (atomic number>3).
Mass extinctions.....??
