September 16 is the International Day for the Preservation of the Ozone Layer. It was designated by the United Nations to commemorate a very important day in world history. Nine years ago, 24 countries met in Montreal and announced to the world that the time had come to stop destroying the ozone layer. In so doing, these countries committed themselves to rid the world of substances that threaten the ozone layer. To-date 155 countries have signed on to one of the most widely recognized international agreement, the Montreal Protocol on Substances that Deplete the Ozone Layer. Why was international action to protect the ozone layer so necessary? The answer is simple: life depends on it.