Phytoplankton are microscopic drifters that photosynthesise and supply a large share of the world's oxygen.

The longer version

Microscopic drifters run the same photosynthesis as land plants, taking dissolved carbon dioxide and releasing oxygen as a by-product. They need both light and nutrients at once, so thickest populations gather where cool currents bring nitrates and phosphates upward from the deep, or where mixing ploughs them back toward the surface.

Blooms fade once supplies are exhausted or grazers catch up. Turnover is measured in days rather than seasons, so a small standing stock still processes enormous quantities of carbon each year. A substantial share of atmospheric oxygen traces back to this quiet marine work.

Where this entry sits

Oceans and Sea Life looks at the salt water that covers most of the planet, from crashing waves and tides to the darkest deep-sea trenches. Expect notes on coral, fish, whales, sharks, jellyfish, shells, and the strange creatures that live far below the surface. The full list sits on the Oceans and Sea Life page, where every entry is listed in order.