The helium in birthday balloons comes from radioactive decay deep within Earth's crust—a process that takes millions of years.

Most of the world's helium is generated through alpha decay of heavy radioactive elements such as uranium-238 and thorium-232, which occur naturally in Earth's crust and have half-lives spanning billions of years. During this decay process, atoms emit alpha particles—each consisting of two protons and two neutrons. When an alpha particle slows down, it captures two electrons from its surroundings to become a stable helium-4 atom.Because helium is a chemically inert noble gas, it doesn't react with other elements. Instead, it migrates through the crust and becomes trapped in impermeable rock layers that also hold natural gas deposits. Geologists estimate that helium concentrations in natural gas must reach at least 0.3 percent for extraction to be economically viable.The United States Federal Helium Reserve, established in 1925 near Amarillo, Texas, once held approximately 30 percent of the world's helium supply. Since the 1900s, the Hugoton Gas Field—spanning Kansas, Oklahoma, and Texas—has been one of the most significant sources of this rare gas.Because helium is a non-renewable resource on Earth, once released into the atmosphere, it eventually reaches the exosphere and is lost to space permanently. Global demand extends far beyond balloons: helium is essential for cooling MRI machines and manufacturing semiconductors. Scientists continue to monitor global reserves as current extraction rates far exceed the millions of years required for radioactive processes to naturally replenish the supply.