Why is photosynthesis important for life on Earth?

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Diagram of a tree leaf illustrating photosynthesis, with arrows showing sunlight, water, and carbon dioxide entering the leaf and sugars and oxygen being produced. A person is shown beside the tree to demonstrate the exchange of oxygen and carbon dioxide between plants and animals. — Photosynthesis Diagram of photosynthesis showing how water, light, and carbon dioxide are absorbed by a plant to produce oxygen, sugars, and more carbon dioxide.

Photosynthesis is essential for life on Earth because it serves as the primary mechanism by which energy enters the biosphere. By converting sunlight, carbon dioxide, and water into chemical energy stored in organic molecules like glucose, photosynthetic organisms act as primary producers that form the base of global food webs.12

Furthermore, photosynthesis is responsible for the presence of nearly all oxygen in Earth's atmosphere. This process, which evolved in ancient bacteria, fundamentally altered Earth's geochemistry and continues to support aerobic life. If photosynthesis were to cease, the majority of organisms would disappear due to a lack of food, and the atmosphere would eventually become depleted of oxygen.13