B2 Reading Multiple Choice Exam 3

The ozone layer

The ozone layer is part of the earth's stratosphere which absorbs most of the sun's UV radiation. It contains high concentrations of ozone, relative to other parts of the atmosphere, although it is still very small relative to other gases in the stratosphere. It is mainly found in the lower portion of the stratosphere, from approximately 20 to 30 kilometres above the earth, though the thickness varies seasonally and geographically, and it absorbs 97–99% of the sun's medium-frequency ultraviolet radiation, which otherwise would potentially damage exposed life forms near the surface. But now human activity, in the form of chlorofluorcarbons is causing irreparable damage to this shield.
Chlorofluorcarbons, usually called CFCs, were identified in 1928 by Thomas Midgley as useful for refrigeration, due to their being stable, non-poisonous, non-corrosive, therefore safe for use with metals, and non-flammable. CFCs were found to be
ideal for coolants in refrigerators and air-conditioners because of their low thermal conductivity, and were widely used as cleaning solvents and in plastic foam for food and drink containers, and in the insulation of buildings during the Second World War. Their use has been so successful that their output has doubled every ten years, and this has contributed to the destruction of the ozone layer.
The problem is that the CFCs, and other gases, are destroying the ozone molecules. Their reaction on the ozone layer is devastating, allowing ultraviolet rays from the sun, known as UV-Bs, to bombard the earth, which cause skin cancer. Medical journals in Australia say two-thirds of the population alive today will develop some form of skin cancer. More than 250,000 of the continent's 16 million inhabitants will develop the deadliest of all, malignant melanoma.
UV-Bs can damage the immune system which leaves the body open to infectious diseases. They can damage the eyes by burning the cornea, injuring the retina and generating cataracts, and in southern Chile, blindness has begun to strike humans, sheep, rabbits and horses. This radiation kills off the plankton, on which larger sea creatures depend, and in southern Chile, a 12 per cent reduction in plankton has been measured.
The scientists dealing with the ozone layer are worried for three main reasons.
Firstly, the ozone depletion is now happening all over the globe, and at a rate which is twice as fast as had been predicted. Secondly, depletion is now being caused by the CFCs released in the mid-1970s, which means the chemicals being released now will endanger our children, and finally, no one knows what the cumulative effects of the depletion of the ozone layer will be, but they do know that things from now on are going to change very quickly indeed.