Ask where Earth gets its oxygen, and many people picture forests first. Trees are the familiar answer. But much of the oxygen produced by photosynthesis begins somewhere very different: in the sunlit surface waters of the ocean, where microscopic organisms drift with the currents.
Roughly half of the oxygen produced through photosynthesis each year comes from the ocean, according to the source material. The main producers are phytoplankton, a huge community of drifting algae, plants and photosynthetic bacteria. They may be too small to see individually, but together they play an enormous role in Earth’s oxygen cycle.
