The ozone layer is a portion of the Earth’s atmosphere which contains relatively high levels of ozone. The Earth’s atmosphere consists of many different layers, and is made up primarily of nitrogen, with oxygen being the second-most common element. The ozone layer is important for a number of reasons, but primarily because it helps to protect life on earth from damaging ultraviolet radiation.

Ozone itself is a particular form of oxygen, where three atoms of the element have bonded together. It is poisonous for us to breathe directly, and is considered a pollutant if it’s found near the surface. The name for ozone comes from the word for the particular smell is it associated with, which occurs during lightning storms.

The ozone layer, like the Earth’s atmosphere itself, has no exact boundary. In general, it is viewed as being the layer of gasses 10 to 20 miles (15-35km) above the Earth’s surface. The concentration of ozone in the ozone layer is high in comparison to anywhere else, but is still relatively low. Even in the most densely-concentrated portions of the ozone layer, ozone makes up only a few parts per million.

Ozone is particularly important to us because it has the unique property of absorbing ultraviolet radiation. There are three main types of ultraviolet (UV) radiation, known as UV-A, UV-B, and UV-C. When functioning properly, the ozone layer completely removes UV-C radiation, which is the most harmful to humans. It also drastically reduces the amount of UV-B that reaches the Earth’s surface — UV-B is the radiation responsible for many types of skin cancer and sunburns.

In the 1970s, it became apparent that the ozone layer was slowly disappearing. It was discovered that this was a direct result of the use of certain catalysts being released in large amounts by humans. A number of countries took small steps to reduce the emission of these catalysts — particularly chlorofluorocarbons (CFCs) — but the steps were generally quite limited. In 1985, however, an enormous hole in the ozone layer was discovered above Antarctica.

This hole in the ozone layer provided the necessary impetus for a worldwide movement to help protect the ozone layer. Within two years of its discovery, the Montreal Protocol was ratified, severely limiting the production of ozone-depleting compounds. By the mid-1990s the use of ozone-depleting compounds had been drastically reduced, and the ozone layer was on its way to recovery.

Although the ozone layer is still well below its historic levels of ozone, its depletion does seem to have slowed dramatically, and the most immediate danger seems to have passed. The ozone layer serves as a poignant example for many people that the nations of the world are capable of taking relatively quick and concrete action in the face of an impending global catastrophe.