9781422285619

INTRODUCTION H umans use a lot of energy. Whether it is to light our homes, cook our food, or power our transit systems, the basic processes of our lives require some type of fuel. In the past, humans depended mostly on wood to sustain themselves. Over time, however, fossil fuels became more prevalent. Fossil fuels are formed by the decomposition of long-dead plants and animals, in processes that take millions of years. One problem with fossil fuels is that they are not renewable; that is, we only have finite amounts of oil,

coal, and natural gas, and once they are used up they are gone for good. Also, the extraction, transportation, and use of fossil fuels can damage our environment.

In Broomfield, Colorado, wood chips are used to create a biofuel called cellulosic ethanol. (US Department of Agriculture/ Wikimedia)

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