how did oxygen first enter earth's atmosphere
Oxygen was first produced on Earth sometime between 2.6 and 2.7 billion years ago. This occurred when a variety of algae, known as cyanobacteria, came into being.hotosynthesis releases oxygen into the Earth's atmosphere through tiny openings on the leaves of plants called stomatas. Photosynthesis is the main source of oxygen and helps to sustain life on Ea... Read More Â».