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ECOSYSTEM

Colorful tropical fish swim through warm water around a coral reef. The fish are part of the coral reef ecosystem. Beautiful orchids grow on trees that tower above the rain forest floor. The orchids and the trees are part of the rain forest ecosystem. A hawk swoops down on a rabbit hopping through the tall grass of a prairie. The hawk, rabbit, and grass are part of the prairie ecosystem.

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POLLUTION

In the mid-1900s, a biologist named Rachel Carson was afraid that some day there might be no more birds. Farmers were spraying a chemical called DDT on their fields to kill insects. But DDT was also keeping birds such as the bald eagle and peregrine falcon from having babies. DDT prevented the babies from hatching. She wrote a book called Silent Spring to warn about the dangers of DDT.
Pollution happens when chemicals that are harmful to living things get into the environment. Rachel Carson feared that DDT would get into the food people ate. Her book scared a lot of people. Governments banned the use of DDT. People then began to worry about other kinds of pollution. They worried that pollution could harm people’s health.

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GLOBAL WARMING
Do you like warm weather?Do you wish it could be warmer still? Be careful what you wish for. The Earth may be moving in that direction. The trend is called global warming.
Not all scientists agree that global warming is happening. Some say it is impossible to know if the climate is changing overall. After all, temperatures vary from day to day and year to year. Most scientists, however, say the trend is up. The warmest days are warmer, the coldest days not as cold. They point out that the ten warmest years of the last century happened after 1980. The three hottest came after 1990. The hottest year on record was 1998.

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