It was matter

Era of matter - a term used in cosmology to determine the phase of the universe's development. Based on the cosmological model of the expanding Universe, it is assumed that the era of matter began about 100,000 years after the Big Bang after the matter became transparent to radiation at the end of the radiation era (relict background radiation) and recombination, or electron capture by protons and nuclei of light elements, primarily helium. The main constituents of matter are hydrogen and helium atoms, accounting for about 35% of the original matter. The matter spread more or less evenly. But accidental density fluctuations have become the source of a stronger gravitational attraction (gravitational instability mechanism), which has spawned galaxy formation and galaxy clusters. The first part of this stage is often referred to as dark ages. Later, when the main form of matter becomes galaxies, it is said to have begun the galactic era, in some sources also called the dark energy era or the star-era.

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