This leads to predicted abundances shown by the circles in the graph, which are in good agreement with observed abundances.
This is an important and detailed test of nucleosynthesis and is further evidence in support of the Big Bang theory.
As lighter stars blow off their outer layers to form planetary nebula, or as heavier stars blast most of their substance into space in a supernova explosion, the fusion products are scattered over wide regions of space.
In order to test the predictions of Big Bang Nucleosynthesis, we need to identify astronomical objects in which the original abundance values are preserved as well as possible - and we need to account for any remaining influences of chemical evolution.
Fortunately for astronomers, there are indicators of how much chemical evolution particular objects have undergone, most importantly the presence of elements such as oxygen and nitrogen.
These are elements with nuclei that are produced by nuclear fusion reactions in stars, but that definitely could not have been produced during Big Bang Nucleosynthesis.
During the first three minutes of the universe, most of the deuterium combined to make helium.
Trace amounts of lithium were also produced at this time.
This process of light element formation in the early universe is called Big Bang nucleosynthesis (BBN).
The predicted abundance of deuterium, helium and lithium depends on the density of ordinary matter in the early universe, as shown in the figure at left.