Question

What caused the composition of Earth’s early oceans to transition from dissolved carbon dioxide to dissolved oxygen?A.

Ultraviolet rays from the Sun converted dissolved carbon dioxide to oxygen.
B.
Excessive rainfall over ocean waters caused carbon dioxide to separate into carbon and oxygen.
C.
Cyanobacteria growing in ocean waters used up carbon dioxide and released oxygen.
D.
Lightning caused the dissolved carbon dioxide in the ocean to decay into oxygen.

Answer 1

Answer: Cyanobacteria growing in ocean waters used up carbon dioxide and released oxygen.

Step-by-step explanation:

Answer 2

C) It's the most certain answer as all animals are believed to have arise from aquatic unicellular bodies that multiplied and evolved into complex organisms. Like all forms of live they respired and took some millions of years to evolve into land animals thus consuming CO2 into O2.