Helium is the second most abundant element in the universe. It is one of the noble gases, and is inert. Helium has replaced hydrogen for use in blimps, since it does not burn. There is practically no helium in the Earth's atmosphere, as it is so light it has all escaped. Helium is obtained from natural gas wells. The helium is produced by the radioactive decay of uranium and thorium deep within the Earth, since a helium nucleus is the same as an alpha particle.
