Abstract

Stone hurts—and not simply because rocks so easily become missiles. The lithic offers a blunt challenge to our belief that humans matter. Homo sapiens are a species perhaps 200,000 years old. Homo erectus and Homo habilis, two of our earliest ancestors, go back perhaps 2.5 million years. That seems a substantial span. If you were to count one number per second and never pause to sleep or eat, it would take about twelve days to reach one million. Two-and-a-half million is a month filled with incessant counting. Stone was the Earth's first solid. Geologists have identified bedrock that has endured at least 4.3 billion years. Some zircon crystals are older still. Every migrant continent harbors rocks of at least...