Earth breathed first 3 billion years ago!

It was generally believed that cyanobacteria, the blue-green algae, that evolved photosynthesis appeared 2.5 billion years ago when the `Great Oxidation Event` (a spike in oxygen levels) happened.

Oxygen may have first accumulated on Earth 3 bln years ago

Oxygen production by photosynthetic cyanobacteria may have initiated as early as three billion years ago, much earlier than previously thought, scientists say.

Oxygen levels on Earth did go up & down: Study

Great Oxidation Event has obvious implications for the origins and evolution of the first forms of eukaryotic life.