What is the ozone layer?
The ozone layer is a region of Earth's stratosphere, about 15 to 35 kilometers up, with high levels of ozone gas. It absorbs most of the Sun's harmful ultraviolet radiation.
Ozone is a form of oxygen made of three oxygen atoms instead of two. In the stratosphere, sunlight splits ordinary oxygen molecules, and the freed atoms combine with other oxygen molecules to form ozone. This layer absorbs most UV-B and nearly all UV-C radiation, which can cause sunburn, skin cancer and damage to plants.
In the 1970s and 1980s, scientists discovered that chemicals called chlorofluorocarbons, or CFCs, used in fridges and spray cans, were destroying ozone. In 1985, researchers reported a large seasonal ozone hole over Antarctica.
A success story
In 1987, countries signed the Montreal Protocol to phase out ozone-depleting chemicals. It is often called the most successful environmental treaty ever. The ozone layer is slowly healing, and UN experts expect it to return to 1980 levels over most of the world by about 2040 and over Antarctica by about 2066.
Did You Know?
Ozone near the ground is a harmful pollutant that forms smog, even though ozone high in the atmosphere protects life.