Physics 3 - Stars and Space - How the Chemical Elements formed

 - Light Elements are formed as a result of fusion in Stars. 

Stars like the Sun fuse Hydrogen nuclei (i.e Protons) into Helium and similar small nuclei including Carbon. When it becomes a Red Giant, it fuses Helium and the other small nuclei into a larger nuclei. 

Nuclei larger than Iron cannot be formed by this process becuase too much Energy is needed.

- Heavy Elements are formed when a massive Star collapses then explodes as a Supernova.

The enormous force of the collapse fuses small nuclei into larger nuclei than Iron. The explosion scatters the Star into Space.

The debris from a Supernova contains all the known Elements from the lightest to the heaviest. Eventually, new Stars form as Gravity pulls the debris together.

Planets form from debris surrounding a new Star. As a result, such Planets will be composed of all the known elements too.