Editing Nucleosynthesis (section)

===Big Bang nucleosynthesis===
{{main|Big Bang nucleosynthesis}}
Big Bang nucleosynthesis<ref>{{Cite web |title=23. Big-Bang Nucleosynthesis |date=September 2017  |first1=B.D. |last1=Fields |first2=P. |last2=Molaro |first3=S. |last3=Sarkar |citeseerx=10.1.1.729.1183 |url=https://pdg.lbl.gov/2017/mobile/reviews/pdf/rpp2017-rev-bbang-nucleosynthesis-m.pdf |archive-url=https://web.archive.org/web/20220401065230/https://pdg.lbl.gov/2017/mobile/reviews/pdf/rpp2017-rev-bbang-nucleosynthesis-m.pdf |archive-date=2022-04-01 |url-status=live   }}</ref> occurred within the first three minutes of the beginning of the universe and is responsible for much of the abundance of {{chem|1|H}} ([[hydrogen-1|protium]]), {{chem|2|H}} (D, [[deuterium]]), {{chem|3|He}} ([[helium-3]]), and {{chem|4|He}} ([[helium-4]]). Although {{chem|4|He}} continues to be produced by stellar fusion and [[alpha decay]]s and trace amounts of {{chem|1|H}} continue to be produced by [[spallation]] and certain types of radioactive decay, most of the mass of the isotopes in the universe are thought to have been produced in the Big Bang. The nuclei of these elements, along with some {{chem|7|Li}} and {{chem|7|Be}} are considered to have been formed between 100 and 300 seconds after the Big Bang when the primordial [[quark–gluon plasma]] froze out to form protons and neutrons. Because of the very short period in which nucleosynthesis occurred before it was stopped by expansion and cooling (about 20 minutes), no elements heavier than [[beryllium]] (or possibly [[boron]]) could be formed. Elements formed during this time were in the plasma state, and did not cool to the state of neutral atoms until much later.{{citation needed|date=December 2012}}

{{Image frame|align=center|width=400|caption=Chief nuclear reactions responsible for the [[abundance of the chemical elements|relative abundances]] of light [[atomic nucleus|atomic nuclei]] observed throughout the universe.
|content=<math chem>\begin{array}{ll}
\ce{n^0 -> p+{} + e^-{} + \overline{\nu}_e} & \ce{p+{} + n^0 -> ^2_1D{} + \gamma}\\
\ce{^2_1D{} + p+ -> ^3_2He{} + \gamma} & \ce{^2_1D{} + ^2_1D -> ^3_2He{} + n^0}\\
\ce{^2_1D{} + ^2_1D -> ^3_1T{} + p+} & \ce{^3_1T{} + ^2_1D -> ^4_2He{} + n^0}\\
\ce{^3_1T{} + ^4_2He -> ^7_3Li{} + \gamma} & \ce{^3_2He{} + n^0 -> ^3_1T{} + p+}\\
\ce{^3_2He{} + ^2_1D -> ^4_2He{} + p+} & \ce{^3_2He{} + ^4_2He -> ^7_4Be{} + \gamma}\\
\ce{^7_3Li{} + p+ -> ^4_2He{} + ^4_2He} & \ce{^7_4Be{} + n^0 -> ^7_3Li{} + p+}
\end{array}</math>}}