Argon on Venus

There is Too much argon 40 on the moon (a recent blog post) and argon in the atmosphere of Venus is hard to understand as well. In both lunar rocks and the atmosphere of Venus the Argon 40/argon 36 ratio is 1:1 while in the atmosphere of Earth argon 40 is 99.6%.

See also 40Ar retention in the terrestrial planets and Geochemistry: Earth holds its breath in Nature 2007.