Primordial, stellar, explosive nucleosynthesis

Nucleosynthesis is the formation of chemical elements.
This primordial process is at the origin of the presence of hydrogen and of helium in the universe.
In stars, these elements fuse together to produce elements of the Mendeleev periodic table up to iron.
Explosions and collisions of stars produce the extreme conditions allowing the fusion of lighter elements to create heavy elements, such as uranium.