Is it true that at one time there was no oxygen?

All people, animals, and plant life require oxygen to thrive. When Earth initially formed, its atmosphere lacked oxygen, the colorless, odorless, and tasteless gas that accounts for around 20% of the air we breathe. It was instead a lethal mixture of hydrogen, methane, ammonia, and hydrogen cyanide. The hydrogen went into space, and the Sun's UV light degraded the combination, leaving just nitrogen and carbon dioxide. Only around 3.4 billion years ago, when life first emerged and photosynthesis (the conversion of light energy into chemical energy by living organisms) began, did oxygen arise.