What is the primary producer of oxygen?

The primary producers of oxygen are photosynthetic organisms, particularly phytoplankton in the oceans, as well as terrestrial plants, including trees and shrubs. Through the process of photosynthesis, these organisms convert carbon dioxide and sunlight into glucose and oxygen. Phytoplankton alone are estimated to contribute around 50-80% of the Earth's oxygen supply, making them crucial for sustaining life on the planet.