What are the primitive organisms thought to have been responsible for the development of Earth's oxygen-rich atmosphere in the Precambrian?

Question

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Cyanobacteria (blue-green algae) are the primitive organisms thought to have been responsible for producing the first oxygen through photosynthesis, which eventually led to the development of Earth's oxygen-rich atmosphere in the Precambrian.

What Are the Primitive Organisms Thought to Have Been Responsible