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.

Question

Quizplus · Accepted Answer

The difficulty in estimating the appearance of cyanobacteria using the oxidation state of the Earth's crust arises because several ancient anaerobic metabolisms can form Fe³⁺ (an oxidized form of iron) without requiring molecular oxygen (O₂). This means that the presence of oxidized minerals in ancient rocks does not necessarily indicate the presence of oxygenic photosynthesis or cyanobacteria, complicating the interpretation of the geological record.

It Is Difficult to Estimate When Cyanobacteria Appeared on Earth