Describing the evolution of humans in the world, McElroy traces our progression from our origins as hunters and gatherers to our organizational growth as we began to domesticate animals and plants, which allowed for the establishment of more sedentary communities. As large numbers of people began to live in the same location for extended amounts of times, local environmental issues began to become significant.

The most significant effect of humans on the environment began 250 years ago with the advent of the Industrial Revolution, which developed energy sources (like coal) not dependant on individual human or animal power and gave us the ability to use remarkable machines to work for us. The Industrial Revolution was not without its problems, however, creating a population flight from countryside to cities, the beginning of the major industrial cities, and especially the consequences of "dirty air."

In the mid-twentieth century, a few major events occurred that shocked people into attempting to clean up dirty air. In 1948, in the valley of Donora, Pennsylvania, pollutants from local coal plants combined with trapped air to produce a lethal cloud. Similarly, in 1952 in London, sooty coal smoke and fog combined to produce "killer smog," causing the deaths of thousands.

Various solutions were attempted. Industry adopted higher smokestacks, believing that the smoke would go somewhere else. In homes heated by coal, a case was made for using higher-quality coal with less particulate matter. Because of these efforts, visible manifestations of pollution were less apparent, but people were still breathing carbon monoxide and the problem remained.

Almost simultaneously, in northern Europe and in northeastern America, people began to focus on a new problem: acid rain. In Scandinavia, in Sweden and Norway, fish were dying. However, when acidity levels in the rain were measured, there were clear indications that coal burned somewhere other than in Sweden and Norway was the obvious source of the acid-causing materials. Pollution — no longer a local problem — was now something that had to be dealt with through international arrangements.

The issue of acid rain was addressed in a serious way in the United States in the 1980's. Problems still remain, however, and although we have reduced emissions have reduced the emission of sulfur compounds into the atmosphere by a variety of means, levels of acidity in the rain are not different from what they were before. Strategies to deal with the problem have been piecemeal: we didn't stop burning coal, we just used technology to try to minimize the damage.