Final answer:
The transition from dissolved carbon dioxide to dissolved oxygen in Earth's early oceans was caused by photosynthesis, a process performed by plants, algae, and some bacteria using sunlight as an energy source.
Step-by-step explanation:
The transition from dissolved carbon dioxide to dissolved oxygen in Earth's early oceans was primarily caused by the process of photosynthesis.
Photosynthesis is a biological process performed by plants, algae, and some bacteria, in which carbon dioxide is converted into oxygen and glucose using sunlight as an energy source.
As more and more photosynthetic organisms evolved and flourished on Earth, they gradually increased the concentration of oxygen in the atmosphere and oceans, leading to the transition from dissolved carbon dioxide to dissolved oxygen.
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