According to the theory of evolution,when did the first photosynthetic organsisms evolve

A.After aerobic prokaryotes.
B.After anaerobic prokaryotes.
C.After heterotrophic eukaryotes.
D.After autotrophic eukaryotes

Ug. I'm surprised they still use the word "prokaryote" in textbooks/lectures! For the love of science, the word prokaryote has been inaccurate since the advent of 16S rRNA signatures during the 1970s. Call them archeae or bacteria.

The first photosynthetic organism arose from cyanobacteria, an aerobic BACTERIA that performs oxygenic photosynthesis (they are autotrophic). These guys came about when the Earth's climate shifted from relatively anoxic to oxygen rich.

Before the aerobic BACTERIA arose, there were anaerobic BACTERIA and ARCHAEA.

The answer is B.

B.