Question

Earlier in history, the earth's atmosphere was most likely not friendly to organisms that needed oxygen to breathe. Today, however, the earth's atmosphere contains the oxygen needed for eukaryotic organisms. The oxygen was produced by cyanobacteria through the process of _____.

volcanism
photosynthesis
metabolism
respiration

Answer 1

Photosynthesis

Step-by-step explanation:

Photosynthesis- Processes That Produce Oxygen