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 cyanobacteria use carbon dioxide for photosynthesis.
Iron oxides form when cyanobacteria use carbon dioxide for photosynthesis.

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.

Answer 1

The correct response is:

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

When photosynthesis occurs, particularly by ancient cyanobacteria, oxygen is released into the atmosphere. This oxygen can react with iron dissolved in water, leading to the formation of iron oxides. The presence of these iron oxides in rock strata is thus evidence that oxygen-producing photosynthesis took place in prehistoric times.