Big Bang Nucleosynthesis

Figure 12 : A graph showing the fractional composition (left axis) of the Universe during the first few minutes after the Big Bang, when nuclear reactions were raging. As time passes (top axis) the temperature of the Universe (bottom axis) drops from 3 billion degrees to a hundred million degrees. After about 20 seconds, helium starts being produced, along with smaller amounts of other light elements (Deuterium, Beryllium, Lithium). The figure was taken from Ed Wrights web notes on cosmology (http://www.astro.ucla.edu/~wright/cosmolog.htm) and was based on calculations published in 1999 by Burles, Nollett and Turner.