Why are iron oxides in rocks evidence for prehistoric photosynthesis?(1 point)

Question

Iron oxides form when oxygen, a product of photosynthesis, is in the atmosphere.
Iron oxides form when carbon dioxide, a reactant of photosynthesis, is in the atmosphere.
Iron oxides form when cyanobacteria produce oxygen via photosynthesis.
Iron oxides form when cyanobacteria use carbon dioxide for photosynthesis.

Answer 1

The correct answer is: Iron oxides form when cyanobacteria produce oxygen via photosynthesis.

This is because the presence of iron oxides in rocks suggests that oxygen was present in the environment, which is a result of photosynthesis carried out by cyanobacteria. These microorganisms are known to have been among the first to perform photosynthesis, releasing oxygen as a byproduct, which then reacted with dissolved iron in the oceans to form iron oxides that became part of the sedimentary rocks.