Potassium argon dating fossils
Rock samples are recorded, marked, sealed and kept free of contamination and excessive heat on the way to the lab.The rock samples are crushed, in clean equipment, to a size that preserves whole grains of the mineral to be dated, then sieved to help concentrate these grains of the target mineral.
These steps help remove as much atmospheric Ar from the sample as possible before making the measurement.
Next, the mineral sample is heated to melting in a vacuum furnace, driving out all the gas.
A precise amount of argon-38 is added to the gas as a "spike" to help calibrate the measurement, and the gas sample is collected onto activated charcoal cooled by liquid nitrogen.
Three argon isotopes are measured: Ar is determined by comparison to it.
Variations in this data may point to errors anywhere in the process, which is why all the steps of preparation are recorded in detail.