In the proton-proton chain, four hydrogen nuclei are converted to a helium nucleus. This does not happen spontaneously on earth because the process requires.

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Four hydrogen nuclei are converted to helium nuclei in the proton-proton chain. This does not occur naturally on Earth because the process requires it. extremely high temperatures, pressures, and densities

The proton-proton chain is a series of reactions that fuses four hydrogen nuclei to form one helium nucleus. The energy is derived from the mass difference between the four hydrogen nuclei with higher masses and the single helium nucleus with lower masses. Energy is released when hydrogen is fused into helium: mass to energy conversion. Because mass is created during the proton-proton chain, energy is released. However, this is essentially the end of the story for the nuclear fusion reactions that occurred in the early Universe, known as Big Bang Nucleosynthesis.

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