Final answer:
When plasma began to form, it led to a significant change in the early stages of the universe. At a few hundred thousand years after the Big Bang, when the temperature dropped and the density of atomic nuclei decreased, the electrons and nuclei combined to form stable atoms of hydrogen and helium. This allowed the universe to become transparent for the first time.
Step-by-step explanation:
Plasma is a hot ionized gas where electrons are stripped off the nuclei, and it occurs naturally in the interiors of stars. When plasma began to form, it led to a significant change in the early stages of the universe. At a few hundred thousand years after the Big Bang, when the temperature dropped and the density of atomic nuclei decreased, the electrons and nuclei combined to form stable atoms of hydrogen and helium. This allowed the universe to become transparent for the first time, as there were no free electrons to scatter photons, and matter and radiation started to evolve separately.