When people think about where Earth’s oxygen comes from, they usually picture forests - especially the Amazon, which gets called the “lungs of the planet.” That’s only half the story. The other half is in the ocean.
Floating throughout the sunlit upper layer of the ocean are uncountable trillions of microscopic plants called phytoplankton. They’re far too small to see, but they photosynthesize just like land plants do - soaking up sunlight and carbon dioxide and pumping out oxygen as a byproduct. Together they produce around 50% of the oxygen in Earth’s atmosphere, more than all the forests on land combined.
That means roughly every other breath you take was made by an organism you can’t see, floating somewhere in the sea. Phytoplankton are also the foundation of almost every ocean food chain - eaten by tiny zooplankton, which feed fish, which feed bigger fish, which feed whales.
