According to the definition of sustainability, the ideal time period to have a sustainable civilization would be forever. 99% of all species that have ever lived on Earth have become extinct. The goal is to allow the human race to stave off extinction for as long as possible, and at least not be responsible for humanity's own negligence. The late Easter Island society is an example of an unsustainable human civilization, which contributed to their extermination. The population of the Easter Island civilization has grown too large and has depleted all of its natural resources at an unsustainable rate; by the time they realized they were low on the trees, it was too late to plant more. Academics such as Paul Ehrlich, author of The Population Bomb, and other neo-Malthusianists dispute that modern society is inclined to end just as the inhabitants of Easter Island did. To avoid such obsolescence, there must be sustainability plans that last centuries and centuries, and hopefully a millennium. Developing a society that can last many centuries and perhaps a millennium will not be an easy task. The most important measure would be to cease the use of non-renewable resources. Coal, oil and natural gas are the least sustainable energy sources we know of, yet our society is dominated by them. About 80% of all energy in the United States is powered by fossil fuels. If the United States