It is difficult to estimate when cyanobacteria appeared on Earth using the evidence from the oxidation state of the Earthʹs crust because

A) several ancient anaerobic metabolisms require O₂.
B) there are multiple forms of anoxygenic photosynthesis.
C) there are multiple groups of oxygenic photosynthetic bacteria.
D) several ancient anaerobic metabolisms form Fe³⁺ without requiring O₂.