<Table> <Tr> <Td> </Td> <Td> This article may be confusing or unclear to readers . In particular, nonspecialists may have trouble understanding this article's language . Please help us clarify the article . There might be a discussion about this on the talk page . (March 2017) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article may be confusing or unclear to readers . In particular, nonspecialists may have trouble understanding this article's language . Please help us clarify the article . There might be a discussion about this on the talk page . (March 2017) (Learn how and when to remove this template message) </Td> </Tr> <P> In physical cosmology, Big Bang nucleosynthesis (abbreviated BBN, also known as primordial nucleosynthesis, arch (a) eonucleosynthesis, archonucleosynthesis, protonucleosynthesis and pal (a) eonucleosynthesis) refers to the production of nuclei other than those of the lightest isotope of hydrogen (hydrogen - 1, H, having a single proton as a nucleus) during the early phases of the Universe . Primordial nucleosynthesis is believed by most cosmologists to have taken place in the interval from roughly 10 seconds to 20 minutes after the Big Bang, and is calculated to be responsible for the formation of most of the universe's helium as the isotope helium - 4 (He), along with small amounts of the hydrogen isotope deuterium (H or D), the helium isotope helium - 3 (He), and a very small amount of the lithium isotope lithium - 7 (Li). In addition to these stable nuclei, two unstable or radioactive isotopes were also produced: the heavy hydrogen isotope tritium (H or T); and the beryllium isotope beryllium - 7 (Be); but these unstable isotopes later decayed into He and Li, as above . </P> <P> Essentially all of the elements that are heavier than lithium were created much later, by stellar nucleosynthesis in evolving and exploding stars . </P>

Neutrons that combined with protons in an atomic nucleus early in the universe's history form