Oxygen Levels Rise
The Earth was a suffocating place until oxygen in the atmosphere slowly began to climb from almost nonexistent levels about 2.5 billion years ago.
1899-12-30 00:00:00 - The Archiver
Breathable air is thought to have been created by cyanobacteria, single-celled microbes living in the sea.
These bacteria harnessed the energy of the sun through photosynthesis-the biochemical process used by plants-producing oxygen as a by-product.
The oxygen-rich ozone layer was also established, shielding the Earth's surface from harmful solar radiation.
Photosynthesis Unleashes Chemical Superweapon: Oxygen