Ar ar dating
Over the past 60 years, potassium-argon dating has been extremely successful, particularly in dating the ocean floor and volcanic eruptions.
K-Ar ages away from spreading ridges, just as we might expect, and recent volcanic eruptions yield very young dates, while older volcanic rocks yield very old dates.
We often take it for granted that measuring chemical concentrations should be an easy task, when it is not.
Measuring the ratio between 40K and 40Ar is especially difficult, because potassium is present in minerals as a .
Of the naturally occurring isotopes of potassium, 40K is radioactive and decays into 40Ar at a precisely known rate, so that the ratio of 40K to 40Ar in minerals is always proportional to the time elapsed since the mineral formed [ 40K is a potassium atom with an atomic mass of 40 units; 40Ar is an argon atom with an atomic mass of 40 units].
This relationship is useful to geochronologists, because quite a few minerals in the Earth’s crust contain measurable quantities of potassium (e.g. In theory, therefore, we can estimate the age of the mineral simply by measuring the relative abundances of each isotope.