Without the protective effect of ozone, life on Earth would not have evolved the way it has. The ozone layer is not evenly distributed around the Earth. The amount of ozone above a location on the Earth varies naturally with latitude, season, and from day to day. Under normal circumstances, the ozone layer is thickest over the poles and thinnest around the equator. The ozone layer over Canada is normally thicker in winter and early spring.
Weather conditions can also cause considerable daily variations.
The ozone layer can slowly rebuild itself if concentrations of ozone-destroying substances are reduced. If our use of damaging chemicals is reduced, the natural balance between ozone creation and destruction can be restored in time. International agreements, like the Montreal Protocol of 1987, now prohibit the manufacture of most ozone-depleting chemicals. This document is also available for download in .pdf format . For help with Adobe Acrobat go to the Virtual Classroom Tips page.