What produces 90% of oxygen?

It may surprise many, but oceans produce up to 90% of the Earth’s oxygen, largely through phytoplankton tiny, photosynthetic organisms living near the water’s surface. These include species of algae, bacteria (like cyanobacteria), and diatoms. They absorb sunlight and carbon dioxide to create food and release oxygen, just like trees do on land.

Although each individual phytoplankton cell is microscopic, the sheer number of them, trillions across all the world’s oceans makes their oxygen output immense. This oxygen not only supports marine life but also rises into the atmosphere for us to breathe.

While rainforests are often called the "lungs of the Earth," they contribute about 20–30% of oxygen production. In contrast, phytoplankton are responsible for the overwhelming majority, making them critical to life on the planet.

Human activities such as ocean pollution, excessive carbon emissions, and climate change are threatening these tiny organisms. Protecting ocean health through sustainable fishing, pollution control, and reducing carbon footprints ensures these natural oxygen factories continue to support life on Earth. In simple terms, most of the air we breathe originates from the ocean’s smallest residents—phytoplankton.