U–Pb geochronology has its roots in a spectacular decade of discovery. Within about ten years of the discovery of radioactivity in 1896, old ideas about the nature of matter were overthrown and the seeds of geochronology were planted. After giants of physics like Ernest Rutherford moved on to other research, Arthur Holmes nurtured the new field of geochronology, combining physics, chemistry, and geology to produce the earliest quantitative geologic timescale. Over the following decades, geochronology experienced a series of revolutionary and evolutionary advances, and became a vital part of almost all fields of geology.