41)__________. The mystery involves a change in the atmoshpere—a hole, or thinning, of the ozone in the atmosphere over Antarctica. Scientists were not sure what was causing it.
42) __________. It is found both in the air we breathe and in the upper atmosphere. Near the earth, ozone in the air is a danger to life. It is a pollutant. But ozone found 10 kilometers to 50 kilometers up in the atmosphere protects life on earth. Ozone forms in the atmosphere through the action of solar radiation. Once formed, the ozone blocks harmful radiation from reaching the earth. Scientists say a decrease in ozone and an increase in the harmful radiation will cause many more cases of skin cancer and will harm crops, animals and fish.
43) __________.
Chlorine is released into the air from the chlorofluorocarbons—or CFCs—used in plastic, air conditioners and spray cans. The use of CFCs has greatly increased worldwide since 1960 and is continuing to increase. The destruction of the ozone in the atmosphere also has increased.
An international effort is being made to halt the loss of atmospheric ozone. But many experts fear the effort will not produce results fast enough to prevent harm to life on earth. Thirty-one nations negotiated a treaty last year (1987) calling for a reduction in the worldwide production of chlorofluorocarbons. It was praised at the time as a major step in halting further destruction of the ozone. Cuts in the present production of CFCs will begin in the mid-1990s.
44) __________.
Harmful chemicals take from 7 to 10 years to rise up into the atmosphere. Damage from the increase use of CFCs in this past decade still has not been felt. Government scientists say more than two times the mount of these gases will be in the atmosphere before the levels stop rising.
45) __________. Scientists point out a molecule of chlorine remains in the atmosphere for as long as 100 years. During that time, it destroys tens of thousands of ozone molecules.
[A] Why has the ozone problem developed? No one knows for sure. But scientists say the evidence is very strong that the chlorine in chlorofluorocarbons (含氯氟烃)is causing much of the problem.
[B] Almost 30 years after scientists discovered that common industrial gases were destroying Earth's protective ozone layer, satellite readings and ground observations show for the first time that the dangerous rate of ozone loss is finally slowing.
[C] Ozone is a three-atom form of oxygen gas.
[D] There have been some new developments in a continuing mystery we have reported about many times.
[E] Scientists also say damage to ozone will continue because of the long life of the chemical gases released into the atmosphere.
[F] The ozone problem caused by CFCs was first noticed as early as the 1960s.
[G] However, most scientists now agree destruction of the ozone will continue for decades. They say this will happen even though industries and governments do their best to control the damage.