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Just like these lines above get thinner and thinner (if you are using Netscape), so does the ozone layer around the earth. Ozone is a naturally occuring gas whose chemical symbol is O3. This is not that much different from the oxygen that we breathe, O2. Ozone has just one more oxygen atom than the oxygen in the air. However, this one tiny difference can make a big effect on our planet. While oxygen in its O2 form is breathable, O3 is harmful to animals if inhaled. However, O3 ozone stays in a layer around the earth. Meanwhile, there is the sun doing it's job of providing light and heat. We can only see a certain range of light, from red to violet, and we see it as the colors of the rainbow. However, there is also light we can't see, outside of what our eyes can detect. Right next to red is the invisible infra-red, which is actually what heats the earth (learn more about the problem this causes in the greenhouse effect). On the other end of the rainbow, just past violet is a light called ultraviolet. We normally know this type of light as the black light, or the glow in the dark light. This light is harmful to life on earth as we know it, and can kill it if we get exposed to it too much. This is where ozone plays its part. Ozone absorbs these ultraviolet rays before it reaches the earth. When it absorbs these harmful rays, a chemical reaction occurs where the ozone is split into oxygen gas (O2) and a free oxygen atom (O). Normally, the parts immediately rejoin together to form ozone again. This is where man and his meddling around steps in. People have made a group of chemicals called ChloroFluoroCarbons, or CFCs. CFCs are found in many items we use, from the air conditioners in cars, to the refrigerators and freezers in our homes, to the hair sprays we use to keep our hair in place, and even to medicinal products such as asthma inhalers. When we use this gas, it rises into the air, and also reacts with ultraviolet light. Here is an illustration of a molecule of a CFC when it reacts with UV light.
As you can see, there is an extra chlorine atom after this reaction. This atom wreaks havoc on our ozone layer. Instead of the O2 and O hooking up after the reaction, instead the O hooks up to the chlorine atom, since the O has a stronger attraction to the chlorine than to the oxygen atom. The new compound of ClO does absolutely nothing for us; it doesn't block the harmful ultraviolet (UV) rays, and allows some more to pass to the earth. Since CFCs were invented this century, more and more ozone is rendered ineffective. Here is an illustration of the whole process (courtesy Time Magazine).
This seems to happen all collect in two areas: the North and South Poles.
As you can see the ClO in the poles is rising, and the ozone levels are dropping to critically low levels. Thinning like this is already occuring over the United States. A complete hole over the U.S. or any populated area would be a complete disaster.
This diagram of the world shows the usage of CFCs in many nations of the world. As can be seen, the U.S., Europe, Japan, and the former Soviet Union were large users of CFCs. It isn't surprising then that the worst thinning of the ozone is occuring directly over these countries.