# How does radiogenic argon-40 get into the atmosphere?

There's an awful lot of argon in the atmosphere: about 0.93% of the atmosphere is argon[1], making it the third-most abundant gas after N2 and O2. As I understand it, most of it is produced by the following decay path:

$$\ce{^{40}_{19}K + ^{0}_{-1}e- -> ^{40}_{18}Ar + \gamma{} + \nu_{e}} %edit$$

How does all this radiogenic argon make it into the atmosphere, though? Most of the decaying potassium-40 must surely be at some depth beneath the surface, thus trapping the argon-40 in the interior of the Earth, right?