Cyanobacteria (image) Arizona State University Caption The orange cells in this microscope image are Synechococcus, a unicellular cyanobacterium only about 1 um in size. Organisms like Synechococcus were responsible for pumping oxygen into the environment 2.5 billion years ago. Credit Susanne Neuer/Amy Hansen Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.