Editing Nucleosynthesis (section)

===Timeline===
It is thought that the primordial nucleons themselves were formed from the [[quark–gluon plasma]] around 13.8 billion years ago during the [[Big Bang]] as it cooled below two trillion degrees. A few minutes afterwards, starting with only [[proton]]s and [[neutron]]s, nuclei up to [[lithium]] and [[beryllium]] (both with [[mass number]] 7) were formed, but hardly any other elements. Some [[boron]] may have been formed at this time, but the process stopped before significant [[carbon]] could be formed, as this element requires a far higher product of helium density and time than were present in the short nucleosynthesis period of the Big Bang. That fusion process essentially shut down at about 20 minutes, due to drops in temperature and density as the universe continued to expand. This first process, [[Big Bang nucleosynthesis]], was the first type of nucleogenesis to occur in the universe, creating the so-called [[primordial element]]s.

A star formed in the early universe produces heavier elements by combining its lighter nuclei{{snd}}[[hydrogen]], [[helium]], lithium, [[beryllium]], and boron{{snd}}which were found in the initial composition of the interstellar medium and hence the star. Interstellar gas therefore contains declining abundances of these light elements, which are present only by virtue of their nucleosynthesis during the Big Bang, and also [[cosmic ray spallation]]. These lighter elements in the present universe are therefore thought to have been produced through thousands of millions of years of cosmic ray (mostly high-energy proton) mediated breakup of heavier elements in interstellar gas and dust. The fragments of these cosmic-ray collisions include [[helium-3]] and the stable isotopes of the light elements lithium, beryllium, and boron. Carbon was not made in the Big Bang, but was produced later in larger stars via the [[triple-alpha process]].

The subsequent nucleosynthesis of heavier elements (''Z''&nbsp;≥&nbsp;6, carbon and heavier elements) requires the extreme temperatures and pressures found within [[star]]s and [[supernova]]e. These processes began as hydrogen and helium from the Big Bang collapsed into the first stars after about 500 million years. Star formation has been occurring continuously in galaxies since that time. The primordial nuclides were created by [[Big Bang nucleosynthesis]], [[stellar nucleosynthesis]], [[supernova nucleosynthesis]], and by nucleosynthesis in exotic events such as neutron star collisions. Other nuclides, such as {{sup|40}}Ar, formed later through radioactive decay. On Earth, mixing and evaporation has altered the primordial composition to what is called the natural terrestrial composition. The heavier elements produced after the Big Bang range in [[atomic number]]s from ''Z''&nbsp;=&nbsp;6 (carbon) to ''Z''&nbsp;=&nbsp;94 ([[plutonium]]). Synthesis of these elements occurred through nuclear reactions involving the strong and weak interactions among nuclei, and called [[nuclear fusion]] (including both rapid and slow multiple neutron capture), and include also [[nuclear fission]] and radioactive decays such as [[beta decay]]. The stability of atomic nuclei of different sizes and composition (i.e. numbers of neutrons and protons) plays an important role in the possible reactions among nuclei. Cosmic nucleosynthesis, therefore, is studied among researchers of astrophysics and nuclear physics ("[[nuclear astrophysics]]").