The isotopes 6Li and 7Li are later partly depleted by proton capture reactions, presumably at the bottom of the convective zone. More recently, the question has changed: The present measurement of helium-4 indicates good agreement, and yet better agreement for helium To do that we need carbon and oxygen and nitrogen and silicon and chlorine and every other naturally occurring element.
The graph above shows the time evolution of the abundances of the light elements for a slightly higher baryon density. A very few helium nuclei combine into heavier nuclei giving a small abundance of Li7 coming from the Big Bang. Further details can be found here.
A similar enigma exists for the deuterium. The goal of the theory of nucleosynthesis is to explain the vastly differing abundances of the chemical elements and their several isotopes from the perspective of natural processes.
These should not be confused with non-standard cosmology: Both theory and observation lead astronomers to believe this to be the case. The fragments of these cosmic-ray collisions include the light elements Li, Be and B. Less than 1 second after the Big Bang, the reactions shown at right maintain the neutron: Without further reactions to preserve neutrons within stable nuclei, the Universe would be pure hydrogen.
Both theory and observation lead astronomers to believe this to be the case. While this theory achieved relative success, it was discovered to be lacking in some important respects. We do not know of course the exact shape of the spectrum giving rise to these Li Be B, but we may assume that they are of the type commonly found in cosmic ray physics: Free neutrons are unstable with a half-life of about ten minutes This section does not cite any sources.
As noted above, in the standard picture of BBN, all of the light element abundances depend on the amount of ordinary matter baryons relative to radiation photons.
This result therefore leads, for the formation of the light elements in the solar system, to a model somewhat different from the FGH one. A few minutes afterward, starting with only protons and neutronsnuclei up to lithium and beryllium both with mass number 7 were formed, but the abundances of other elements dropped sharply with growing atomic mass.
Interstellar gas therefore contains declining abundances of these light elements, which are present only by virtue of their nucleosynthesis during the Big Bang. See Handbook of Isotopes in the Cosmos for more data and discussion of abundances of the isotopes.
Using this value, are the BBN predictions for the abundances of light elements in agreement with the observations?. The observed lithium abundance in stars is less than the predicted lithium abundance, by a factor of about 2.
But stars destroy lithium so it is hard to assess the significance of this difference. Other Big Bang Nucleosynthesis pages: LBL, Martin White.
The Lithium - 7 discrepancy dates back to the earliest stages of the Universe ie. from 10 seconds to 20 minutes after the Big Bang. It was only after 10 seconds of Big Bang that temperatures were suitable enough for the formation of nuclei of first three elements - H, He and Li by the process of Big Bang Nucleosynthesis (BBN).
Big Bang nucleosynthesis produced very few nuclei of elements heavier than lithium due to a bottleneck: the absence of a stable nucleus with 8 or 5 nucleons.
This deficit of larger atoms also limited the amounts of lithium-7 produced during BBN. NUCLEOSYNTHESIS OF LI, BE, AND B TOTAL YIELD (IN mb) OF THE MASS NUMBER 7 OR 6 ON "C AND AT 12C TABLE IX VARIOUS ENERGIES, h E, (MeV) 44 50 0-(6Li + e) 0-(7Li) a('Be) n7/n6 F, (MeV) a(6Li -}- 6He) f 18 =L 5.
It is believed to be responsible for the formation of hydrogen (H-1 or simply H), its isotope deuterium (H-2 or D), the helium isotopes He-3 and He-4, and the lithium isotope Li The observed lithium abundance in stars is less than the predicted lithium abundance, by a factor of about 2.
But stars destroy lithium so it is hard to assess the significance of this difference. Other Big Bang Nucleosynthesis pages: LBL, Martin White.Lithium 7 nucleosynthesis