Helium is formed through the natural decay of radioactive materials – like uranium and thorium – within the Earth’s crust. Because it is lighter than air, the vast majority of the helium that leaks into the atmosphere eventually escapes into outer space. The 5.2 parts per million that remain in the Earth’s atmosphere are too widely dispersed to be collected economically. Therefore helium must be recovered as a byproduct of natural gas while it is still trapped beneath layers of nonporous rock.
While helium is the second most common element in the universe it is getting increasingly more scarce on Earth.