The ozone layer is one layer of the stratosphere, the second layer of Earth’s atmosphere. The stratosphere is the mass of protective gases clinging to our planet.

The stratosphere gets its name because it is stratified, or layered: as elevation increases, the stratosphere gets warmer. The stratosphere increases in warmth with elevation because ozone gases in the upper layers absorb intense ultraviolet radiation from the sun.

Ozone is only a trace gas in the atmosphere—only about three molecules for every 10 million molecules of air. But it does a very important job. Like a sponge, the ozone layer absorbs bits of radiation hitting Earth from the sun. Even though we need some of the sun's radiation to live, too much of it can damage living things. The ozone layer acts as a shield for life on Earth.

Ozone is good at trapping a type of radiation called ultraviolet radiation, or UV light, which can penetrate organisms’ protective layers, like skin. This then may damage DNA molecules in plants and animals. There are two major types of UV light: UVB and UVA.

UVB is the cause of skin conditions like sunburns, and cancers like basal cell carcinoma and squamous cell carcinoma.

People used to think that UVA light, the radiation used in tanning beds, is harmless because it doesn’t cause burns. However, scientists now know that UVA light is even more harmful than UVB, penetrating more deeply and causing a deadly skin cancer, melanoma, and premature aging. The ozone layer, Earth’s sunscreen, absorbs about 98 percent of this devastating UV light.

The ozone layer is getting thinner. Chemicals called chlorofluorocarbons (CFCs) are a reason we have a thinning ozone layer. A CFC is a molecule that contains the elements carbon, chlorine, and fluorine. CFCs are everywhere, mostly in refrigerants and plastic products. Businesses and consumers use them because they're inexpensive, they don't catch fire easily, and they don't usually poison living things. But the CFCs start eating away at the ozone layer once they get blown into the stratosphere.

Ozone molecules, which are simply made of three joined oxygen atoms, are always being destroyed and reformed naturally. But CFCs in the air make it very difficult for ozone to reform once it’s broken apart. The ozone layer, which only makes up 0.00006 percent of Earth’s atmosphere, is getting thinner and thinner all the time.

“Ozone holes” are popular names for areas of damage to the ozone layer. This is inaccurate. Ozone layer damage is more like a really thin patch than a hole. The ozone layer is thinnest near the poles.

In the 1970s, people all over the world started realizing the ozone layer was getting thinner and that this was a bad thing. Many governments and businesses agreed that some chemicals, like aerosol cans, should be outlawed. There are fewer aerosol cans produced today. The ozone layer has slowly recovered as people, businesses, and governments work to control such pollution.