This is a method based on the radioactive decay of isotopes of uranium. It has proved particularly useful for the period 500,000 - 50,000 years ago, which lies outside the time range of radiocarbon dating. In Europe, where there are few volcanic rocks suitable for dating by the potassium-argon technique, uranium series (U-series) dating may be the method of first choice for clarifying when a site was occupied by early humans.