Energy may be obtained directly from an energy source, as when people burn wood to produce heat. Energy may also be obtained indirectly. For example, at a power plant, oil is burned to create steam and that steam produced is used to power a generator which is used for electricity.

Energy that is produced by businesses and the government and then sold to the public is called commercial energy. About 85 percent of all commercial energy comes from petroleum, coal, and natural gas. Petroleum, coal, and natural gas are called fossil fuels because they developed from the fossilized remains of prehistoric plants.

The earth contains only a limited supply of fossil fuels. But the amount of fossil fuel burned by people to produce energy has nearly doubled every 20 years since 1900. It is projected that soon, the supply will run out. Scientists and engineers are working to develop other sources of energy.

To make our existing energy resources last longer, scientists and engineers are working to develop more efficient methods of recovering, transporting, and using energy. Petroleum and mining experts are investigating more economical ways of removing oil, natural gas, and coal from the earth. In addition, engineers are designing more efficient transportation systems to reduce the loss of energy as fuel is transported.

All other sources of energy also have environmental effects. Nuclear power plants create thermal pollution and radioactive wastes. The construction of large dams changes river conditions. Electric power lines produce electromagnetic fields that may create a health hazard. Geothermal power plants release heat and gases into the atmosphere. Any use of energy, no matter how clean the source; it will give off waste heat. If the use of energy continues to grow, the heat released could alter the environment of many cities.

Scientists have many problems to solve before new sources of energy become useful. Nuclear physicists have not yet produced a reliable fast breeder. To turn solar energy into a practical power source, scientists must find better ways to gather, concentrate, and store it. They also must find new ways to recover the energy contained in solid and liquid wastes.

erious problems. They include the depletion of fuel reserves and environmental effects.

The production, transportation, and use of fossil fuels all affect the environment. Oil spills are a big problem associated with the environment. Oil spills pollute the ocean, contaminate beaches, and kill wildlife. Burying oil pipelines requires changes in the environment, such as the clearing of trees along the route. Underground coal mines can cave in and can release dangerous gases. Strip mining has caused land erosions. The burning of coal and oil pollutes the air with nitro

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