What has created at least half of the oxygen in Earth's atmosphere?

Question

Quizplus · Accepted Answer

Phytoplankton in the ocean are responsible for at least half of the oxygen in Earth's atmosphere through photosynthesis. Trees in the boreal forest and plants, algae, and phytoplankton in the intertidal zone also contribute oxygen, but not as significantly as phytoplankton. Burning fossil fuels does not create oxygen, but instead releases carbon dioxide into the atmosphere.

What Has Created at Least Half of the Oxygen in Earth's