Which Plants Produce the Majority of Earth's Oxygen?

Since childhood, we've been told that forests are the “lungs” of the planet. We're taught that it’s the trees that produce most of the Earth's oxygen. But that's not entirely true. Yes, green plants do produce oxygen through photosynthesis (absorbing carbon dioxide and releasing oxygen), but forests turn out to be far from the main source of this vital gas.

Forests produce oxygen — but consume it too

According to scientists, all the plants on Earth release about 150 billion tons of oxygen annually. That sounds like more than enough. However, around 60% of that amount is immediately used up in processes of decay and oxidation — the decomposition of fallen leaves, dead plants, and animals. The rest is consumed by living beings during respiration.

Take tropical forests, for example. These are some of the most vibrant and densely populated ecosystems on Earth — everywhere, something is breathing or decomposing. Such forests do generate a lot of oxygen, but they also consume huge amounts. In fact, they produce just about as much as they need for themselves.

In temperate forests (such as coniferous forests), the situation is a bit better — biodiversity is lower, and some oxygen can escape into the atmosphere. But even they cannot be considered the main suppliers of oxygen for humanity.

So who produces the oxygen?

The answer may surprise you: the primary producers of oxygen on Earth aren’t trees, but microscopic algae that live in the seas and oceans. We're talking about phytoplankton — tiny organisms that float in the water column. They play a crucial role in sustaining life across the planet.

Microscopic algae: the main source of oxygen

Despite their size, phytoplankton produces more oxygen than all forests and land plants combined. It includes unicellular green algae and cyanobacteria (blue-green algae), which are found in massive quantities throughout the world's oceans.

One of the most remarkable species is Prochlorococcus, the smallest photosynthetic cell on Earth. This microscopic organism is estimated to produce up to 20% of all oxygen in the biosphere. That’s more than all the planet’s tropical forests combined — and it’s just one species among many in the phytoplankton group!

So why are marine algae so efficient? It’s because phytoplankton produces far more oxygen than it needs for its own respiration. It’s estimated that, overall, oceanic phytoplankton generates about 10 times more oxygen than it consumes. In addition, much less oxygen is needed for the decomposition of organic matter in water than on land. As a result, around 40% of the oxygen produced by phytoplankton is not used up locally and escapes into the atmosphere — spreading with the wind across the globe.

The whole world breathes thanks to marine algae

Phytoplankton is a quiet, invisible hero. Thanks to its work, air is enriched with oxygen even in parts of the world without green vegetation: deserts, mountains, ice shelves, and megacities. Without it, life on Earth as we know it would not be possible.

It not only nourishes the oceans but also supports the respiration of billions of land-dwelling creatures — including us.

Why does it matter?

Understanding this system changes how we see nature. While caring for forests, we must not forget about the oceans. Even microscopic algae play a vital role in the life of the planet. That’s why protecting the marine environment and its inhabitants is just as important as conserving forests.

Every ecosystem on Earth serves its purpose. And the health of the entire planet depends on our attention and respectful treatment of nature.