Final answer:
Banded iron formations reveal early Earth conditions by providing evidence of the emergence of photosynthetic organisms and the availability of oxygen and carbonates on early Earth.
Step-by-step explanation:
Banded iron formations reveal early Earth conditions. The alternating dark-coloured and iron-rich bands, composed of hematite and magnetite, formed when water with high concentrations of dissolved oxygen precipitated these minerals. The light-coloured and iron-poor shale or chert bands formed under conditions with high concentrations of carbonates. These formations provide evidence of the emergence of photosynthetic organisms and the availability of oxygen and carbonates on early Earth.