Matter Domination -
We have seen that over time, the energy densities of matter and energy equalized until at around 50,000 to 70,000 years, the energy density of the Universe becomes dominated by matter. The temperature remains high enough that the hydrogen and helium atoms remain ionized, that is, they have not combined with electrons. Thus, the atoms remain positively charged, and continue to interact with photons. Matter here would also include cold or warm dark matter; that is, all matter that is moving at non-relativistic speeds (speeds well below the speed of light). According to the Lambda Cold Dark Matter model, cold dark matter dominates the Universe at this stage. This permits gravitational collapse to make the very slightly more dense regions caused by quantum mechanical irregularities during cosmic inflation become denser, ultimately leading to the formation of the structures we see in the Universe. Unfortunately, while there are strong theories for how the baryonic matter formed, the LambdaCDM model does not provide any mechanism for the formation of the CDM.
It was thought that matter domination has continued to this day, but recent evidence shows that the rate of expansion of the Universe started to increase some 6 or 7 billion years ago, leading to the conclusion that energy, in the form of dark energy, may have reversed the matter domination so that we are in an era of dark energy domination.
Astronomy & Cosmology -
The Early Universe
(or "What Banged in the Big Bang?")