Timelapse microscope footage of a mat of cyanobacteria bubbling as it produces oxygen through photosynthesis. Photosynthesis is the process by which organisms use the energy of sunlight to turn atmospheric carbon dioxide into energy-rich sugars, releasing oxygen as a waste product. Cyanobacteria were the first photosynthetic organisms on Earth, and were responsible for oxygenating the atmosphere some 2.3 billion years ago. It is thought that the chloroplasts found in plant cells derived from symbiotic cyanobacteria that lived within the cells of the ancestors of plants and algae.