The ozone layer is one layer of the stratosphere, the second layer of the 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 3 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, damaging 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, our 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 chlorofluorocarbon (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 that 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.

ozone layer
The amount of ozone in the atmosphere is measured in "Dobson units."

Million to One
Compared to other gases in the atmosphere, ozone is pretty rare. According to NOAA, there are only about three molecules of ozone for every ten million molecules of air.

absorb
Verb

to soak up.

aerosol can
Noun

container of liquid material under high pressure. When released through a small opening, the liquid becomes a spray or foam.

Noun

layers of gases surrounding a planet or other celestial body.

cancer
Noun

growth of abnormal cells in the body.

chlorofluorocarbon (CFC)
Noun

chemical compound mostly used in refrigerants and flame-retardants. Some CFCs have destructive effects on the ozone layer.

cling
Verb

to attach or stick to.

consumer
Noun

person who uses a good or service.

damage
Noun

harm that reduces usefulness or value.

devastate
Verb

to destroy.

DNA
Noun

(deoxyribonucleic acid) molecule in every living organism that contains specific genetic information on that organism.

element
Noun

chemical that cannot be separated into simpler substances.

Noun

height above or below sea level.

gas
Noun

state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.

government
Noun

system or order of a nation, state, or other political unit.

inaccurate
Adjective

untrue.

melanoma
Noun

dangerous and sometimes fatal skin cancer.

molecule
Noun

smallest physical unit of a substance, consisting of two or more atoms linked together.

outlaw
Verb

to make illegal or against the law.

oxygen
Noun

chemical element with the symbol O, whose gas form is 21% of the Earth's atmosphere.

ozone hole
Noun

circular pattern, usually located near the Antarctic, of thin atmospheric ozone, which absorbs harmful ultraviolet sunlight.

Noun

layer in the atmosphere containing the gas ozone, which absorbs most of the sun's ultraviolet radiation.

penetrate
Verb

to push through.

plastic
Noun

chemical material that can be easily shaped when heated to a high temperature.

poison
Noun

substance that harms health.

pole
Noun

extreme north or south point of the Earth's axis.

Noun

introduction of harmful materials into the environment.

radiation
Noun

energy, emitted as waves or particles, radiating outward from a source.

refrigerant
Noun

substance used to keep materials cool.

skin
Noun

soft external covering of some animals.

sponge
Noun

substance that easily absorbs other material.

stratify
Verb

to divide into layers.

stratosphere
Noun

level of Earth's atmosphere, extending from 10 kilometers (6 miles) to 50 kilometers (31 miles) above the surface of the Earth.

ultraviolet radiation
Noun

powerful light waves that are too short for humans to see, but can penetrate Earth's atmosphere. Ultraviolet is often shortened to UV.

UVB
Noun

type of ultraviolet (UV) radiation that can cause sunburn, skin cancer, and types of eye damage.

volcanic eruption
Noun

activity that includes a discharge of gas, ash, or lava from a volcano.