How would earth's atmosphere be different if organisms capable of photosynthesis has not evolved?

The world would be very different if green plants had not evolved because the world is based on green plants. They provide food for almost all organisms: plants, animals, and microorganisms. They release oxygen into the atmosphere. They provide people with products including building materials, medicines, fuels, and fibers. They form fossil fuels, which are used by people all over the world. None of this would exist without green plants. The world would be much less colorful and diverse as well, because we would not have the great variety of plants, including trees and flowers, we have now.

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