Noun

(head)

.

*{{quote-magazine, year=2013, month=September-October, author= Katie L. Burke

, magazine=(American Scientist), title= In the News , passage=Oxygen levels on Earth skyrocketed 2.4 billion years ago, when cyanobacteria evolved photosynthesis: the ability to convert water and carbon dioxide into carbohydrates and waste oxygen using solar energy.}}