Most of Earth's oxygen is produced by the ocean, not by forests.

Scientists estimate that 50% to 80% of the oxygen production on Earth comes from the ocean. The majority of this production is from oceanic plankton, which includes drifting plants, algae, and some bacteria that can photosynthesize. One particular species, Prochlorococcus, is the smallest photosynthetic organism on Earth, yet it produces up to 20% of the oxygen in our entire biosphere.This process occurs primarily in the upper layers of the ocean, known as the euphotic zone, where sunlight can penetrate deep enough to power photosynthesis. Phytoplankton contain chlorophyll to capture sunlight and use it to convert water and carbon dioxide into energy. While they consume oxygen during respiration just like animals, the net output they provide is essential for life on land.Research from NASA and the National Oceanic and Atmospheric Administration (NOAA) highlights that while rainforests are often called the lungs of the planet, they actually consume nearly as much oxygen as they produce through the decay of organic matter. In contrast, a significant portion of the oxygen produced by phytoplankton remains in the atmosphere. This cycle has been stable for millions of years, maintaining the roughly 21% oxygen levels we breathe today.The health of these marine populations is critical for global climate stability. Changes in ocean temperature and acidity can affect phytoplankton growth rates and distribution. Monitoring these microscopic organisms remains a top priority for climate scientists studying the long-term oxygen balance of our atmosphere.