Final answer:
Helium mainly originates from the Big Bang and stellar nucleosynthesis. Immediately after the Big Bang, a high percentage of helium was formed, which cannot be explained by stellar processes alone. Stars contribute to the cosmic helium inventory by fusing hydrogen and, to a lesser extent, through the decay of heavier earthly elements.
Step-by-step explanation:
The origin of helium can be traced back to two main processes: stellar nucleosynthesis and the Big Bang. During the first few minutes after the Big Bang, around 25% of the matter in the universe became helium, which is a higher percentage than what can be produced by stars alone. This primordial nucleosynthesis addresses the mystery of why there is so much helium in the universe – it cannot be accounted for solely by the processes occurring in stars.
In stars, helium is also formed through nuclear fusion, where hydrogen atoms combine under immense pressure and temperatures. For stars more massive than about eight solar masses, this fusion process can lead to the creation of elements as heavy as iron. When these stars exhaust their fuel and die, they eject matter enriched with heavy elements into space, contributing to the cosmic abundance of elements including helium. In addition to stellar sources, a minor contribution to Earth's helium comes from the radioactive decay of heavier elements found in the Earth's interior.