Questions & Answers

Hole in the 'Zone

Do you have questions? Our experts have answers to some of your most frequently asked questions.

How long has the Earth's ozone layer been there?

Atmospheric scientists believe that Earth's protective ozone layer has been around for about 600 million years. Ozone in the atmosphere gradually built up as a result of photosynthetic organisms (green plants, algae, and bacteria) putting oxygen in the air.

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Besides protecting us from ultraviolet radiation, how else has ozone affected life here on Earth?

Without a protective ozone layer, it would have been very difficult for life forms to make the jump from the ocean environment to the land. Early life forms stayed submerged in the oceans because it was water's job to protect them from the effects of UV radiation. Once the protective ozone layer formed, animals and plants could venture out of the water onto the land and rapidly evolve to fill all the new ecological niches the terrestrial environment offered.

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When and how did scientists first discover the ozone hole?

First using high-altitude weather balloons and then satellites orbiting high above the Earth, scientists have had an idea that ozone was being depleted in the stratosphere (the upper atmosphere) since the mid-1960s. But the actual Glossary Link ozone holeOzone hole: Lies approximately 15-40 kilometers (10-25 miles) above the Earth's surface in the stratosphere. It protects the Earth from receiving harmful rays from the sun. Depletion or thinning of this layer leads to an increased number of skin cancers, eye problems, and other health concerns. over Antarctica wasn't reported until 1985.

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How do scientists monitor the level of ozone in the stratosphere?

Ozone concentration in the upper atmosphere is monitored by a combination of high-altitude weather balloons and satellite images.

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Doesn't ozone get destroyed naturally by UV radiation in the stratosphere?

While it is true that ozone molecules are constantly being destroyed by incoming UV radiation from the sun, once the molecules have been split up, they also tend to naturally recombine with each other to produce new ozone. For the most part, under natural conditions, the amount of ozone destroyed by radiation is balanced by the amount of new ozone forming, so scientists consider the total amount of ozone to be in "equilibrium."

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People mostly talk about the ozone hole over Antarctica. Is there one over the North Pole, too?

Indeed there is. Stratospheric ozone depletion is happening over both poles, although the "hole" is not as well-defined in the northern hemisphere as it is in the south.

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Why does most stratospheric ozone depletion happen over the poles?

Studies have shown that the cold, still air over the poles during the long, dark winter causes a buildup of ice crystals high in the stratosphere. These crystals then provide a place for chlorine atoms from CFCs (chlorofluorocarbons) to cling on to and build up. When the spring comes and the area begins to heat up, the ice crystals melt and the chlorine is then released into the air. That's when the chlorine reacts with the ozone molecules. Although there is some ozone loss over temperate and tropical regions, not as much reactive chlorine accumulates because they don't get the same buildup of ice crystals in the stratosphere during the winter months.

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Will the ozone hole recover if we stop using destructive chemicals?

Absolutely! In fact, since the use of some CFCs were banned by a number of industrialized countries, the ozone hole over Antarctica has shown signs of closing. But the problem took years to develop, so you can't expect the solution to happen overnight. One of the problems is that CFCs are really stable chemicals and, once they get into the air, it may take 50 to 100 years for them to break down. In addition, CFCs in the troposphere (the layer of the atmosphere close to the Earth) take time to make it up to the stratosphere (some atmospheric scientists estimate as much as 40 years). This means that even if we were to stop using all destructive chemicals today, it could be as much as a century before there is a total recovery.

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Are CFCs the only human-made chemicals responsible for destroying the ozone layer?

No, but they are by far the biggest problem. Other destructive chemicals include halons and bromine (which are found in fire extinguishers) and nitric acid, which comes from the exhaust of high-flying, supersonic transport planes such as the Concorde. There may in fact be more "ozone eaters" out there that scientists have not yet identified.

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Do people with darker skin have less to worry about from UV radiation than light skinned people do?

All people, regardless of the color of their skin, must be concerned about exposure to UV radiation. However, melanin (the pigment in the skin that gives it its dark color) does keep darker-skinned people from getting sunburned as quickly as fair-skinned individuals and can protect them from cancer and some of the long term damaging effects of UV radiation. Therefore, fair-skinned individuals need to take more care in protecting themselves from too much sun exposure.

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Do all sunglasses help protect the eyes from UV exposure?

While all sunglasses cut down the amount of visible light and glare, only sunglasses that are rated for UV protection will safeguard your eyes against the dangerous ultraviolet part of the spectrum.

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