What gas was not present in the atmosphere of primitive earth?

Primitive Earth (Before life) contained no or very little Oxygen (element#8)

According to scientific theory:

Earth had no oxygen to begin with. It had a lot of carbon dioxide, though. Somehow (We still do not know how they started growing) single-celled Carbon Dioxide-breathing bacteria slowly, over thousands to millions of years, turned most carbon dioxide into oxygen, supporting new types of life.

:)