The simple explanation is...
Helium is naturally occurring. The helium we use for balloons and other uses mainly comes from mining underground gas pockets of helium.
Helium is extracted in a few places in the world, namely USA, Algeria, Russia and Qatar – the largest contributors of helium to the world markets.
The scientific explanation is....
Helium is the second-most common element in the universe; in our solar system it is mostly on the sun. The helium found on Earth was created over millions of years by the decay of metals and elements underground On Earth it is relatively rare — 5.2 ppm by volume in the atmosphere. Most terrestrial helium present today is created by the natural radioactive decay of heavy radioactive elements (thorium and uranium, although there are other examples), as the alpha particles emitted by such decays consist of helium-4 nuclei. This radiogenic helium is trapped with natural gas in concentrations up to 7% by volume, from which it is extracted commercially by a low-temperature separation process called fractional distillation. Previously, terrestrial helium was thought to be a non-renewable resource because once released into the atmosphere, it readily escapes into space. However, recent studies suggest that helium is produced deep in the earth by radioactive decay, and that large untapped reserves may exist under the Rocky Mountains in North America and in natural gas reserves.
|»||Chemical symbol: He|
|»||Second lightest elemental gas, after hydrogen|
|»||Smallest of all molecules|
|»||Lowest boiling point of any element (-452.1°F, -268.9°C, 4.2 K, 7.6 R)|
|»||Seven times lighter than air|
|»||Conducts sound three times faster than air|
|»||Has five times air's thermal conductivity|
|»||Does not become radioactive under irradiation|
|»||Slightly soluble in water|
|»||High thermal conductivity|
In the Environment
|»||Helium is produced continually by the radioactive decay of uranium and other elements, gradually working its way into the atmosphere|
|»||Helium atoms are light enough to escape the Earth's gravitational field and into space|
|»||Commercial extraction from air is impractical because helium's concentration is only about five parts per billion|