Commentator: Many people argue that the release of chlorofluorocarbons into the atmosphere is harming humans by damaging the ozone layer, thus allowing increased amounts of ultraviolet radiation to reach Earth  But 300, 000 years ago a supernova greatly damaged the ozone layer, with no significant effect on our earliest ancestors
Because the supernova' s disruption was much greater than the estimated effect of chlorofluorocarbons today, there is no reason to think that these chemicals in the atmosphere harm humans in this way
Extraterrestrial influences on the ozone layer tend to occur less often than terrestrial ones.