It Is Difficult to Estimate When Cyanobacteria Appeared on Earth

question 37

Multiple Choice

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.

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