Frogs, toads and salamanders usually make us think of green, slimy little monsters. These monsters actually belong to a very special class of animals called the amphibians. Amphibians can live both on land and in the water. They commonly inhabit ponds, rivers, marshes and other wetlands.
Today, amphibians are becoming extinct very quickly from all the six continents where they are found. More than 25 countries are reporting sharp drops in the populations of amphibians. In some places, embryos (胚胎) are dying; in others, adults are missing. Why are they dying off?
Scientists blame human interference. Industrial waste and toxic gases given out by factories, manufacturing plants and cars are steadily poisoning the breeding grounds of amphibians. Chemicals such as sulphur dioxide rise high into the atmosphere and mix with rain. This makes the rain acidic and thus kills off delicate amphibian embryos.
More rare species of amphibians are already gone. Costa Rica's Golden toads have not been seen since 1989. The Australian Gastric Brooding frogs are extinct. Leopard frog numbers are dropping in the Rocky Mountains. Leopard frogs live in the wetland regions in these areas. The wetlands are being drained to make way for highways, industry and new housing.
Another threat to the amphibians is the increased ultraviolet radiation. Ultraviolet rays come from the sun and are extremely harmful to living things. They can cause skin cancer in humans. Luckily for us, ultraviolet rays are blocked by a thick layer of ozone above the earth's atmosphere. Ozone is a special kind of oxygen which absorbs ultraviolet radiation. Now, the ozone layer is being destroyed by chemicals called CFC's which are given off by factories. A hole in the ozone layer was discovered over Antarctica in the late 1980’s. As a result, more ultraviolet rays are reaching the earth and more amphibians are dying.
Just as the emergence of new infectious diseases such as Bird Flu are a threat to human and animal populations across the world, amphibian species are also facing their most significant threat from a little understood disease. A chytrid fungus is understood to be of the major causes of frog death across the world.
(Note: Answer the questions or complete the statements in NO MORE THAN TWELVE WORDS)
81. _____________________________________indicate that amphibians are dying out quickly.
82. What’s the destructive force of acid rain?
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83. The ozone layer protects people by _____________________________________________.
84. List at least two major factors that lead to the extinction of amphibians.
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