Occurrence in Nature

 

Helium is the second most abundant element after hydrogen in the universe and in the solar system. About 11.3 percent of all atoms in the universe are helium atoms. By comparison, about 88.6 percent of all atoms in the universe are hydrogen. Thus, at least 99.9 percent of all atoms are either hydrogen or helium atoms.

By contrast, helium is much less abundant on Earth. It is the sixth most abundant gas in the atmosphere after nitrogen, oxygen, argon, carbon dioxide, and neon. It makes up about 0.000524 percent of the air.

It is probably impossible to estimate the amount of helium in the Earth's crust. The gas is produced when uranium and other radioactive elements break down. But it often escapes into the atmosphere almost immediately.

There are no known health hazards resulting from exposure to helium.