Values for abundances are difficult to determine with much certainty, so all values should be treated with some caution, especially so for the less common elements. Local concentrations of any element can vary from those given here by orders of magnitude. Its origin in these gases is traced to the decay of radioactive elements in rocks. Some minerals contain occluded helium and this can be liberated by heating.
Some rocks consist of minerals which contain uranium and potassium.
These decay to helium and argon and analysis of these gases can be used to determine the age of the rock. Helium is the second most abundant element in the universe. It is very common in the hotter stars. It is an important component in the proton-proton reaction and the carbon cycle in stars.