The first stars which were probably formed only 200 million years after the big bang were made up of most entirely of hydrogen and helium -- virtually no other chemicals were present. They would have been extremely large and hot. Pretty much 100 to 1,000 times the mass of the sun, they only lasted a few million years. Ultraviolet light from these stars may have triggerd a movement in the evolution of the universe. The Reionization of its hydrogen, turning it from neutral gas back into the ionized (electronically charged) form seen today. Alternatively, radiation from quasars may have reionized the universe. :)