The ozone layer

The ozone layer -- which helps protect the Earth from potentially dangerous ultraviolet rays that can cause skin -- began developing holes on an annual basis starting in the 1980s due to widespread use of chlorofluorocarbons, or CFCs.CFCs are now almost non-existent thanks to an international treaty signed in Montreal in 1987, and the UN says the Ozone layer is "well on track" for recovery by mid-century, although fixing it over Antarctica would take longer.VIDEOGRAPHIC