It is estimated that oxygen production first evolved in photosynthetic prokaryotes approximately 2.7 billion years ago. The first photosynthetic prokaryotes are presumed to be similar to today's cyanobacteria.
Which of the following best supports the claim that photosynthetic prokaryotes were responsible for the oxygen in Earth's atmosphere?
a. The light reactions of photosynthesis split carbon dioxide into carbon and oxygen.
b. The light reactions of photosynthesis split water into hydrogen ions and oxygen.
c. The Calvin cycle splits glucose into carbon, hydrogen, and oxygen.
d. The Calvin cycle splits water into hydrogen ions and oxygen.
