Nucleosynthesis
Nucleosynthesis in general refers to the process of synthesizing, or creating, nuclei. This is most commonly seen today in stars, such as our sun, where hydrogen is constantly becoming helium through the process of nuclear fusion. However, mind blowing physics is more concerned with primordial nucleosynthesis: the final stage of the Big Bang.
Nucleosynthesis began 3 minutes after the Big Bang and continued for approximately 17 minutes, accounting for the abundance of lighter elements, such as hydrogen and helium, in the universe. Another reason for the abundance of light elements is that nuclei with no electrons to balance charge can only grow a little heavier before decaying back into light elements.
Nucleosynthesis - Image declared public domain
EXAMPLE NUCLEOSYNTHESIS REACTION:
A proton and a neutron yield a gamma ray and a deutron (the nucleus of deuterium, a proton and a neutron)
Xavier Stone
Sources and Links
http://www.einstein-online.info/en/spotlights/BBN/index.html