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E nergy continues to be one of the most hotly debated topics in America today. Public discussion often focuses on issues related to Americans’ use of fossil fuels such as oil, coal, and gasoline. With topics like gasoline prices and global warming in the news almost every day, Americans are also talking about al- ternative sources of energy that could replace fossil fuels. These alternative energies include solar, wind, and water power, and fuel made from trees, plants, and waste products. History tells us that these sources of energy, now viewed as alternatives, were once the primary sources of energy used by people to heat their homes, cook their food, and do their work. A look at the chang- ing use of energy over time can help in understanding how Americans became dependent on fossil fuels and how earth’s original sources of energy came to be seen as alternatives. Using Energy All of earth’s life forms use energy to survive. In nature, plants and trees get energy from sunlight through the photosynthesis process. Energy from the sun and wind drive earth’s water cycle, a critical support system for life. Wind energy helps the pollina- tion process of some plants and trees and moves water on the surface of lakes and oceans to create waves. The energy of water moving in rivers and waterfalls is powerful enough to carve mountains into valleys and canyons and to carry rocks and soil to new locations. Earth itself is full of energy from its under- ground center of hot molten rock, which creates heat known as geothermal energy. All of these different types of energy work together to support life on earth.