I work at the interface between chemistry and two other disciplines, geology and archaeology. One way to determine the age of materials is to look at the damage caused by radioisotopes in the material and its surroundings. The older the object, the more damage should be found. The extent of damage can be measured with electron spin resonance (ESR), a technique that looks at the unpaired electrons created when a stable bond is broken by radiation. Projects in the past few years have included determining Late Stone Age dates at Olduvai Gorge, clarifying the transition from Neanderthals to Homo sapiens in Central Europe, and discovering the use of fire in South Africa 1.5 million years ago. Current projects are taken from sites in India, Brazil, Africa, and Europe.