In BCE 13,699,997,983, The Universe was Beginning.
The Big Bang, the event responsible for the creation of the universe, produced atoms of hydrogen and helium. Over time, the hydrogen and helium (henceforth referred to as H and He respectively) were drawn together by gravity into heated clumps of gas called stars.
Stars cause fusion into other, gradually heavier atoms, in a precise order, detailed below. The elements are H, He, Carbon(C), Neon(Ne), Oxygen(O), Silicon(Si), and Iron(Fe).
H > He
He > C
C > Ne
Ne > O
Si > Fe
Iron, however, is unable to fuse. Star collapse occurs once a sizable iron core is created. In large stars, this leads to a supernova occurring. This causes the fusion of those atoms into different atoms.