Does nuclear fussion occur naturally?

In order to bring nuclei together so that fusion can occur, these strong repulsive forces must be overcome. This can be done through pressure, temperature, or, for example, by accelerating the particles to high speeds and then making them collide (in a particle accelerator). Atoms and nuclei experience strong electrostatic repulsion forces (between electrons and protons, respectively), which increase exponentially as they get closer to one another (the force obeys the ubiquitous "inverse square law").

Nucleosynthesis, another name for the process of fusing lighter atomic nuclei into heavier ones, is called nuclear fusion.

There came a time when the conditions were right for the fusion of hydrogen into Deuterium, Helium 3, and Helium 4, as well as small amounts of Lithium and Beryllium. The early Universe consisted of Hydrogen. The first naturally occurring fusion reactions happened soon after the Bi Bang in what is known as Big Bang Nucleosynthesis.

The primary natural fusion reactors are stars. Stars are formed when gas and dust clouds collapse due to gravity, raising temperatures and pressures to a point where the strong nuclear force can overcome positively charged protons' electrostatic repulsion to initiate and sustain fusion reactions.

Fusion reactors hold great promise for producing large amounts of clean energy, but the challenge lies in maintaining the high temperatures and pressures necessary for a sustained fusion reaction.

No, nuclear fusion requires extremely high temperatures and pressures, which are found in stars and during hydrogen bomb explosions. It does not happen naturally on Earth under normal conditions.