Question

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

Iron oxides form when carbon dioxide, a reactant of photosynthesis, is in the atmosphere.
Iron oxides form when carbon dioxide, a reactant of photosynthesis, is in the atmosphere.

Iron oxides form when oxygen, a product of photosynthesis, is in the atmosphere.
Iron oxides form when oxygen, a product of photosynthesis, is in the atmosphere.

Iron oxides form when cyanobacteria produce oxygen via photosynthesis.
Iron oxides form when cyanobacteria produce oxygen via photosynthesis.

Iron oxides form when cyanobacteria use carbon dioxide for photosynthesis.

Answer 1

Iron oxides form when oxygen, a product of photosynthesis, is in the atmosphere.

Explanation: oxygen produced by photosynthetic organisms (e.g., cyanobacteria) oxidized dissolved iron (Fe2+) to Fe3+, which precipitated as iron oxides (banded iron formations).