•supernova remnants indicate that on average the event occurs about three times every century in the Milky Way. They play a significant role in enriching the interstellar medium with higher mass elements.  Furthermore, the expanding shock waves from supernova explosions can trigger the formation of new stars (http://en.wikipedia.org/wiki/Supernova ).
•A near-Earth supernova is a supernova close enough to the Earth to have noticeable effects on its biosphere ( termed the zone of life on Earth). It could be as far as 3000 light-years away. Gamma rays from a supernova would induce a chemical reaction in the upper atmosphere converting molecular nitrogen into nitrogen oxides, depleting the ozone layer enough to expose the surface to harmful solar radiation .
•In 2009, elevated levels of nitrate ions were found in Antarctic ice (جليد القطب الجنوبي), which coincided (تزامنت) with the 1006 and 1054 supernovae. Gamma rays from these supernovae could have boosted levels of nitrogen oxides (عززت مستويات أكاسيد النيتروجين), which became trapped in the ice