This latter decay branch has produced an isotopic abundance of argon on Earth which differs greatly from that seen in gas giants and stellar spectra.
[citation needed] 40K is the largest source of natural radioactivity in healthy animals and humans, greater even than 14C.
Minerals are dated by measurement of the concentration of potassium and the amount of radiogenic 40Ar that has accumulated.
[citation needed] All other potassium isotopes have half-lives under a day, most under a minute.
The least stable is 31K, a three-proton emitter discovered in 2019; its half-life was measured to be shorter than 10 picoseconds.