Ruddiman begins the book with a brief introduction to the science of climate change and the various individuals that have been key in influencing the field over the years. He also notes that the earth's climate has been drifting toward cooler temperatures for the last 55 million years. The dominant hypothesis for this trend is that large volcanic eruptions have subsided while increasing amounts of carbon dioxide have been absorbed out of the atmosphere due to interactions between monsoon rains and ground up rock exposed by India pushing into Asia and creating the Himalayas. Additionally it is believed that the melting ice that produced higher sea levels resulted in the ocean absorbing more carbon dioxide out of the atmosphere. These two natural occurrences resulted in less carbon dioxide in the atmosphere hence possibly producing the general cooling trend.