Two critical requirements must be met before light elements, like hydrogen or helium, will fuse and form heavier elements. the two requirements for nuclear fusion are

Explanation:

Nuclear fusion is the union of the protons and neutrons of two atoms to form a single atomic nucleus, of greater weight than those that gave rise to it.

In this process, an amount of energy equivalent to the difference between the binding energy of the new atom and the sum of the energies of the initial atoms is released.

For the fusion process to occur, it is necessary to overcome the electric repulsion force between the two nuclei, which grows in the direct ratio of the distance between them. This is only possible with extremely high temperatures, these reactions are also called thermonuclear reactions.

not too sure but maybe in the hot springs.