Helium (He), atomic number 2, is the lightest noble gas. This colorless, odorless, and non-toxic gas is notable for its inert, unreactive nature. It also has the lowest boiling point among all elements.
Helium’s Cosmic Abode
Helium is the second most abundant element in the observable universe, making up about 24% of its total elemental mass, surpassed only by hydrogen. Much cosmic helium originated during the Big Bang nucleosynthesis, when light nuclei like helium-4 formed. Stars, including our Sun, continuously produce new helium through nuclear fusion, converting hydrogen into helium in their cores. This element is a significant component of gas giants like Jupiter, and is also found in vast interstellar clouds and nebulae, typically composed of about 90% hydrogen and 10% helium.
Underground Reservoirs
On Earth, helium’s primary source is within underground natural gas deposits. This terrestrial helium (helium-4) forms through the radioactive decay of heavy elements like uranium and thorium in the Earth’s crust. During this decay, alpha particles (helium nuclei) are emitted; these particles then acquire electrons to become neutral helium atoms. This newly formed helium migrates upwards through rock formations, becoming trapped in non-porous geological structures, often accumulating alongside natural gas. Significant extractable reserves are in the United States (Great Plains: Kansas, Oklahoma, Texas), Qatar, Algeria, Russia, Canada, and China.
Fleeting Atmospheric Presence
While helium exists in Earth’s atmosphere, its presence is limited to trace amounts (around 5.2 parts per million by volume). This scarcity is due to helium’s exceptionally light atomic mass and non-reactive nature. Unlike heavier gases, helium atoms in the upper atmosphere can readily achieve escape velocity, causing them to drift off into space and leading to a continuous loss of atmospheric helium.
The Rarity Paradox
Despite its cosmic abundance, helium is considered a finite and non-renewable resource on Earth. This terrestrial scarcity stems from its slow formation through radioactive decay over millions of years, its tendency to escape Earth’s atmosphere once released, and the specific geological conditions required for its accumulation in underground reservoirs. Once helium escapes into the atmosphere, it is effectively lost to space, making its replenishment on Earth a geological process that takes immense timescales. The limited availability of extractable helium, coupled with its increasing demand, highlights its precious nature.