Origin of iron oxide spherules in the banded iron formation of the Bababudan Group, Dharwar Craton, Southern India

► Hydrothermal iron-oxide spherule formation in Archean BIFs. ► Carbonaceous matter in iron-oxide spherules related to the hydrothermal event at 2.52 Ga. ► Low mature carbonaceous matter around iron-oxide spherules related to modern weathering. ► Martian surface iron oxides should be investigated for carbonaceous matter.