The main components of the atmosphere of the primitive Earth were carbon dioxide, nitrogen and water vapor. Oxygen was not present at the time. Life born on the Earth transformed it into the only planet with an atmosphere containing oxygen. The oxygen created by life in turn impacted the evolution of new life forms. The activities of these new life forms reduced the availability of carbon dioxide, which had been so abundant in the atmosphere of primitive Earth. As a result, the atmosphere was slowly shifted to one characterized by a large amount of oxygen. Eventually the era of great bio-dominance appeared on the Earth.