What is the Ozone Layer?

by Fraser Cain on August 22, 2009

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Ozone layer hole. Image credit: NASA

Ozone layer hole. Image credit: NASA


The ozone layer is a region in the Earth’s atmosphere that contains high concentrations of ozone. Ozone is three molecules of oxygen bonded together, and so it has the chemical symbol O3. The ozone layer contains more than 91% of the ozone in the Earth’s atmosphere. Because it absorbs ultraviolet radiation from the Sun, the ozone layer is vital to the evolution and survival of life on Earth.

Ozone in the Earth’s atmosphere is created when sunlight strikes oxygen molecules which consist of two oxygen atoms bonded together (O2). This splits it into two separate oxygen atoms which float in the atmosphere until they bond with other oxygen molecules creating ozone (O3). Ozone is unstable, though, and further ultraviolet radiation continues to break up the ozone into oxygen molecules and single oxygen atoms. This combination and breakdown is going all the time in the ozone layer.

The ozone layer is special to life because it absorbs ultraviolet radiation from the Sun in a very specific wavelength – UV-B radiation, between 315-280 nanometers in wavelength. It’s this UV-B radiation which gives us sunburns and can even cause cancer with long term radiation. Without the ozone layer, we would receive much more harmful radiation from the Sun.

Of course, one of the big worries in the last few years is the problem of ozone depletion. Certain manmade chemicals, like nitric oxide and chlorofluorocarbons break down ozone molecules, stopping them from being able to absorb ultraviolet radiation. A single molecule of one of these free radicals can break down more than 100,000 ozone molecules.

Satellites observing the Earth’s atmosphere discovered that the ongoing use of these chemicals were causing the ozone layer to thin out. Ozone layers declined at a rate of 4% per decade, mostly over the Earth’s northern and southern poles. Many countries enacted bans of ozone-destroying chemicals in 1978, and in the last few years scientists have determined that the rate of ozone depletion is slowing down.

We have written many articles about the ozone layer for Universe Today. Here’s an article about the ozone success story, and here’s an article about how the ozone layer really looks like it’s recovering.

Here’s more information on the ozone layer from NASA’s Ozone Resource Page. And here’s the ozone hole watch site.

In episode 36 of Astronomy Cast we discussed how an gamma ray burst could strip away the ozone layer of the Earth in just a moment.

About 

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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