Improvements in potassium‐argon dating: 1962–1975

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Abstract
Since its development in the 1950s, potassium‐argon dating has seen several modifications. The original method of measuring the total potassium and the three isotopes of argon in a sample then multiplying by factors to determine the amount of potassium‐40 and the amount of radiogenic argon in the sample is still in use, and is known as the conventional K/Ar method. Modifications to the conventional method have been largely in improved instrumentation and automation of the procedure, the data being handled directly by computer. Beginning in 1962, a method of potassium‐argon dating involving neutron activation of the sample with fast neutrons to produce argon‐39 from the potassium‐39 was developed and is known as the 40Ar/39Ar method. A sample of known age and potassium content is activated at the same time as the unknown and used to calibrate the neutron flux and the age of the unknown. The method obviates the need for separate potassium determinations and permits multiple age determinations on a single sample by incremental heating during the argon extraction, thus yielding more information about the sample and greater precision in the age determination than in the conventional method. Multiple mineral age determinations on a single sample by either method, however, are preferable to a single determination, no matter how precise, as is illustrated by the difficulties encountered in dating the hominid‐bearing beds at East Rudolf, Kenya.