Where did oxygen come from in the earth’s atmosphere?

Initially, carbon dioxide predominated in the Earth’s atmosphere. Free oxygen began to accumulate as a result of various biological processes; green plants are the main source of free oxygen in the earth’s atmosphere.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.