Natural Disaster - Asteroid impact is the top reason why it should be taken seriously. There is a great chance that a cosmic interloper will hit Earth, and according to Harry's research, we won't have to wait millions of years for it to be a reality. History is full with such kind of events, and one of them occurs in 1908, when a 200-foot-wide comet fragment pierced through the earth's atmosphere and exploded over the Tunguska region in Siberia and Russia. Astronomers believe that similar-sized events occur every one to three centuries.
Gamma-ray Burst - Another reason which Harry Coumnas thinks could be possible, is a Gamma-ray burst. Once a day or so, one would see a bright flash appear in the sky for a short time, which outshine everything else, then goes away. According to him, these gamma-ray bursts originate in far distant galaxies and are 10 quadrillion (a one followed by 16 zeros) times more powerful than the sun. Once the burst starts, it is for sure that, there would be no escaping from its fury. The atmosphere of earth will surely offer the initial protection from most of the burst's deadly X rays and gamma rays, but at a cost.