Ar ar dating method
It is based on the fact that some of the radioactive isotope of Potassium, Potassium-40 (K-40) ,decays to the gas Argon as Argon-40 (Ar-40).
By comparing the proportion of K-40 to Ar-40 in a sample of volcanic rock, and knowing the decay rate of K-40, the date that the rock formed can be determined.
One thing to keep in mind is that high-precision isotope measurements always measure ratios between isotopes, not absolute concentrations.
To understand argon-argon dating, you need to understand potassium-argon dating.
Potassium-Argon Dating Potassium-Argon dating is the only viable technique for dating very old archaeological materials.
Geologists have used this method to date rocks as much as 4 billion years old.
The calcium-potassium age method is seldom used, however, because of the great abundance of nonradiogenic calcium in minerals or rocks, which masks the presence of radiogenic calcium.
Thus, the ratio of argon-40 and potassium-40 and radiogenic calcium-40 to potassium-40 in a mineral or rock is a measure of the age of the sample.
As the K-40 in the rock decays into Ar-40, the gas is trapped in the rock.
In this simulation, a unit of molten rock cools and crystallizes. Note that time is expressed in millions of years on this graph, as opposed to thousands of years in the C-14 graph.
Potassium (K) is one of the most abundant elements in the Earth's crust (2.4% by mass).
One out of every 10,000 Potassium atoms is radioactive Potassium-40 (K-40).