Which process is most responsible for the increase in early Earth's atmospheric oxygen levels?

1. Outgassing

2. Condensation

3. Photosynthesis

4. Precipitation

The answer is photosynthesis

The answer is photosynthesis. Photosynthesis is the process by which green plants and certain other organisms transform light energy into chemical energy. During photosynthesis in green plants, light energy is captured by the chlorophyll in the leaves and used to convert water, carbon dioxide, and minerals into oxygen and energy rich compounds. It is important because all living things need oxygen to survive. All producers make oxygen and sugar for the other consumers.