Archaeometry

The potassium-argon method of dating allows scientists to date rocks that were formed between 50,000 and two billion years ago. The rate at which argon 40 forms from the decay of potassium 40, one of the most common minerals in the earth's crust, is known. Therefore, it is possible to determine the age of an object based on the accumulation of argon 40 in the specimen. The first archeological site to be dated by this method (using lava samples) was at Olduvai Gorge in Tanzania.