Question

multiple choice 1 point
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 todays cyanobacteria. which of the following best supports the claim that photosynthetic prokaryotes were responsible for the oxygen in
earths atmosphere?
the light reactions of photosynthesis split carbon dioxide into carbon and oxygen.
the light reactions of photosynthesis split water into hydrogen ions and oxygen
the calvin cycle splits glucose into carbon, hydrogen, and oxygen.
the calvin cycle splits water into hydrogen ions and oxygen.

Explanation:

The light reactions of photosynthesis split water into hydrogen ions and oxygen. Cyanobacteria are photosynthetic prokaryotes. If oxygen production in early photosynthetic prokaryotes (like cyanobacteria) was similar to today's cyanobacteria, and the light reactions split water (as in modern photosynthesis which produces oxygen from water - splitting in light reactions), this supports the claim that they were responsible for Earth's oxygen. The Calvin cycle uses products of light reactions (not splitting water/glucose etc. in the way described in wrong options).

Answer:

The light reactions of photosynthesis split water into hydrogen ions and oxygen.