Most of the world’s oxygen is made in the ocean by plants and other living things. But one species of phytoplankton (a plant-like bacteria) called prochlorococcus makes so much oxygen that it's responsible for the equivalent of one in every five breaths we take. It's tiny 100 laid end to end are the width of a single human hair but it is one the most numerous life forms on Earth. It's estimated there are up to 3 octillion world wide. That's 3 followed by 27 zeros!