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THE OZONE LAYER

What is the ozone layer?

The ozone layer is part of the stratosphere, a layer of the Earth's atmosphere that lies about 10 to 30 miles (16 to 48 kilometers) above the surface of the Earth. Ozone (O3) is like regular gaseous oxygen (O2) with an extra oxygen atom attached to it. It

Before the ozone layer was discovered, someone must have discovered ozone. Who was that?

Dutch chemist Martinus van Marum (1750-1837) discovered ozone around the year 1785, while conducting experiments with electricity. As many high school science students now do, van Marum smelled a distinctive odor while working with oxygen and electricity. Van Marum, who is also credited with discovering carbon monoxide, did not, however, identify the source of the odor as a unique gas molecule. It was not until 1840 that German-Swiss chemist Christian Friedrich Schonbein (1799-1868) correctly identified ozone as a gas, which he named after the Greek ozein, meaning "smell." Finally, Swiss chemist J.L. Soret worked out its chemical structure as being a molecule consisting of three bonded oxygen atoms (O3).

is created when short-wavelength ultraviolet radiation interacts with O2 molecules. The energy from the radiation breaks the molecules apart, which then recombine into ozone.

The ozone layer is important because it protects life on Earth from harmful ultraviolet radiation. While it does not absorb all of this radiation (otherwise, it would be impossible for you to get a tan!), it prevents about 80 percent of it from reaching life on Earth. As anyone who knows about melanoma can tell you, too much ultraviolet radiation can lead to cancer.

Who discovered the ozone layer?

In 1913, French physicists Henri Buisson (1873-1944) and Charles Fabry (1867-1945; full name, Marie Paul Auguste Charles Fabry) theorized that an ozone layer existed in the upper atmosphere. It was confirmed in a series of measurements of ultraviolet radiation levels that were recorded by W.N. Hartley and A. Cornu from 1879 to 1881.

How did Charles Fabry discover that the ozone absorbs ultraviolet light?

Fabry (1867-1945) invented the interferometer (a device measuring how light waves interfere with each other) with fellow French physicist Albert Pérot (1863-1925). He used this Fabry-Pérot interferometer to measure the Doppler effect on light in the laboratory. Then, in a 1913 experiment, he used it to learn that UV radiation is absorbed by the ozone layer.

Has there always been an ozone layer?

No. Before plants evolved on the planet, there was no ozone layer, because plants are responsible for converting carbon dioxide in the atmosphere into oxygen molecules. So, life on Earth actually began to evolve before there was an ozone layer.

This 1987 image of the ozone hole over the Antarctic was taken by the NOAA-9 environmental satellite. (NOAA)

This 1987 image of the ozone hole over the Antarctic was taken by the NOAA-9 environmental satellite. (NOAA)

If ozone is good for us, why do we hear about ozone alerts and "bad ozone"?

Ozone is great when it is high up in the atmosphere and doing its job of protecting us from radiation, but when it is down near ground level it is toxic to those who breathe it in. Car exhaust fumes and other sources of pollution include ozone, which is seen in smog. Ozone pollution can make people sick and damage crops. Small amounts of ozone are also produced by electrical storms (if you have ever performed electricity experiments in a high school or college laboratory, you might be familiar with the ozone smell produced by even small bolts of electricity).

What are some other effects of ultraviolet radiation?

Small amounts of ultraviolet (UV) radiation can actually be good for you because it aids in the production of Vitamin D in the body. However, you only need about 10 to 15 minutes of sunlight exposure a day to get this benefit (not getting enough sunlight leads to Vitamin D depletion, which can lead to depression and other symptoms in humans and is, indeed, a chronic problem in populations located in northern and extreme-southern climates).

Besides the risks of cancer—especially melanoma—overexposure to UV radiation can cause cataracts or inflammation of the cornea ("snow blindness"). If exposure is not too long, the eye can heal itself from this inflammation, but prolonged

What is the Umkehr effect?

Swiss astronomer Paul Gotz published a paper in 1931 in which he described how ultraviolet light is affected by the ozone layer. Ozone absorbs different wavelengths of light in the ultraviolet range at varying amounts, and these amounts change depending on the angle of the Sun in the sky ("umkehr" is German for "change" or "convert"). Measuring the difference between the amount of light being received at the two wavelengths can tell scientists how much ozone is in the atmosphere.

exposure could lead to permanent blindness; cancer of the eye is also a possibility. It is also believed that too much UV radiation weakens immune systems, though studies are still being conducted to more fully understand this health risk. Interestingly, it has also been found that, in areas where ozone levels are lower and more UV radiation penetrates to ground level, certain construction materials such as wood and some plastics degrade at a higher rate than normal.

High UV levels also, of course, affect plants and animals, though some are at a higher risk than others. Scientists have learned, for example, that soy bean crops and some types of rice could die if the ozone were too severely depleted. Also, young pine tree needles are damaged by UV light, but mature needles, which have a waxy coating, are protected. In the oceans, some forms of plankton could die or be severely depleted if the ozone was not doing its job. The result would be a breakdown in ocean food chains that could be devastating. The effects on wild animals are not well known, though nocturnal animals would likely be unaffected, and many diurnal animals have fur or feathers that protect them from radiation. However, skin around the eyes and ears are often more exposed to the sunlight, and animals would be as susceptible to eye problems as much as humans.

 
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