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

    Photograph by Suzailan Shoroyo, MyShot

    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.

    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.

  • Term Part of Speech Definition Encyclopedic Entry
    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.

    atmosphere Noun

    layers of gases surrounding a planet or other celestial body.

    Encyclopedic Entry: atmosphere
    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.

    elevation Noun

    height above or below sea level.

    Encyclopedic Entry: elevation
    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.

    ozone layer Noun

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

    Encyclopedic Entry: ozone layer
    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.

    pollution Noun

    introduction of harmful materials into the environment.

    Encyclopedic Entry: pollution
    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

    highest 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.

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