Argon is the one of the possible products of radioactive decay of potassium (the other is calcium). The lithosphere of the Earth has a lot of potassium. As an inert gas, the argon isn't doing much of anything. read more
If Earth's atmosphere weighs around 5*10^12 kg and argon is around 1.3% by weight, that is around 7*10^10 kg of argon. Considering that potassium-40 is a small fraction of potassium and 90% of decays do not result in argon-40, around 10^4 times as much potassium was necessary in the earth to give rise to the argon in the atmosphere, on the order of 10^15 kg of potassium. read more
Atmospheric Argon, the abundance of this element in the atmosphere as an indicator of the age of the earth. atmospheric argon The existing atmosphere surrounding the earth contains a little less than one percent of the inert gas Argon, an approximate total of 6.59 x 10 19 grams. read more