How would earths atmosphere be different if organisms capable of photosynthesis has not evolved?

In a world where photosynthetic plants have not evolved, everything would be extremely different. The world is based on green plants which provide food for almost all living organisms, provide us with products like medicine and materials, and they form fossil fuels, which are used by just about everyone around the world. The world would be much less colorful and diverse, and there would not be any animals as these plants are food for a lot of animal species we have now. We humans might have not even lasted very long without green plants. Not only are they food sources, but they help circulate oxygen and carbon dioxide in the environment.

the oceanic zone is typically defined as the area of the ocean lying beyond the continental shelf, but operationally is often referred to as beginning where the water depths drop to below 100 meters (328 feet), seaward from the coast to the open ocean.

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