English novelist and scientist C. P. Snow classed certain scientific ideas with the works of Shakespeare as something every educated person should know. One such idea, according to Snow, was the second law of thermodynamics, which deals with the diffusion of heat and has many profound consequences. He might well have added Newton's laws, the periodic table of elements, the double-helix structure of DNA, and scores of other masterpieces of scientific discovery.
Four billion years ago, the infant Earth was a seething cauldron of erupting volcanoes, raining meteors, and hot noxious gases, totally devoid of life. But a relatively short time later—100 to 200 million years—the planet was teeming with primitive organisms. What happened?