From The Habitable Planet, an online book about the Earth by Annenberg Learner.
The Field Museum provides this page on how ancient charcoal can reveal information about past atmospheric oxygen.
News & Events
A Scientific American article on how ancient, tiny organisms created the air we breathe.
A N.Y. Times article exploring scientific methods to understand how oxygen developed on Earth.
Google - Research database allows searching of the scholarly literature.
An interactive tool from the Smithsonian Institution that allows you to change the amounts of oxygen, carbon dioxide, and ozone in a test atmosphere.
This interactive from PBS allows you to see how important not only the presence but the precise amount of oxygen is to life on Earth.