We know that there is a thick layer (or blanket) of ozone gas in the upper atmosphere which acts as a preventive shield against the harmful ultra-violet rays. This is because the ozone layer present in upper atmosphere absorbs most of the ultra-violet radiations coming from the sun. This highly useful ozone layer in the upper atmosphere has been threatened by a wide range of human activities. This is discussed below. In the year 1980, scientists noted a hole in the ozone layer (or ozone blanket) which covers the upper atmosphere. This ozone hole was detected over the region of Antarctica.
The ultra-violet rays which were earlier almost completely blocked by this ozone layer can now enter the earth's lower atmosphere to some extent through this ozone hole. This will gradually increase the level of ultra-violet radiations reaching the earth's surface. High levels of this ultra-violet radiation are harmful to nearly all forms of life. The ultra-violet rays can cause skin cancer. So, the most alarming effect of increase in ultra-violet radiation on earth's surface due to ozone hole might be an increase of skin cancer among men and animals. The excessive ultra-violet radiation also harms the plants.
We shall now discuss the causes for the depletion of the ozone layer and formation of ozone hole. One of the important causes for the formation of ozone hole is the use of chemicals known as chloro-fluoro-carbons (like dichloro-difluoro-methane, CC12F2). The chloro-fluoro-carbons which are used in spray cans and a& refrigerants, react with the ozone layer and destroy it. Since the chloro-fluoro-carbons deplete the useful ozone layer, so their use is now being banned throughout the world to protect the ozone layer. The emissions produced by supersonic jet aeroplanes and nuclear explosions also cause the depletion of ozone layer in the upper atmosphere. Before we go further and discuss oceans.